one end of the .001 mfd. grid condenser and the other end of this with
the grid of the vacuum tube. Connect the telegraph key, the buzzer and
the dry cell in series and then shunt them around the grid condenser.
Next connect the plate of the tube with one end of the .001 mfd.
blocking condenser and the other end of this with the clip _2_ on the
tuning coil.
Connect one end of the filament with the + or positive electrode of
the storage battery, the - or negative electrode of this with one post
of the rheostat and the other post of the latter with the other end of
the filament; then connect clip _3_ with the + or positive side of the
storage battery. This done connect one end of the choke coil to the
conductor that leads to the plate and connect the other end of the
choke coil to one of the taps of the switch on the panel cut-out.
Connect the + or positive electrode of the storage battery to the
other switch tap and between the switch and the choke coil connect the
protective condenser across the 110 volt feed wires. Finally connect
the lamp cord from the socket to the plug fuse taps when your
experimental continuous wave telegraph transmitter is ready to use.
A 100 Mile C. W. Telegraph Transmitter.--Here is a continuous
wave telegraph transmitter that will cover distances up to 100 miles
that you can rely on. It is built on exactly the same lines as the
experimental transmitter just described, but instead of using a 100
volt plate amplifier as a makeshift generator of oscillations it
employs a vacuum tube made especially for setting up oscillations and
instead of having a low plate voltage it is energized with 350 volts.
The Apparatus You Need.--For this transmitter you require: (1) one
_oscillation transformer_; (2) one _hot-wire ammeter_; (3) one _aerial
series condenser_; (4) one _grid leak resistance_; (5) one _chopper_;
(6) one _key circuit choke coil_; (7) one _5 watt vacuum tube
oscillator_; (8) one _6 volt storage battery_; (9) one _battery
rheostat_; (10) one _battery voltmeter_; (11) one _blocking
condenser_; (12) one _power circuit choke coil_, and (13) one
_motor-generator_.
The Oscillation Transformer.--The tuning coil, or _oscillation
transformer_ as this one is called, is a conductively coupled
tuner--that is, the primary and secondary coils form one continuous
coil instead of two separate coils. This tuner is made up of 25 turns
of thin copper strip, 3/8 inch wide and with its edges rounded, and
this is secured to a wood base as shown at A in Fig. 77. It is fitted
with one fixed tap and three clips to each of which a length of copper
braid is attached. It has a diameter of 6-1/4 inches, a height of
7-7/8 inches and a length of 9-3/8 inches, and it costs $11.00.
[Illustration: Fig. 77.--Apparatus of 100 Mile C. W. Telegraph
Transmitter.]
The Aerial Condenser.--This condenser is made up of three fixed
condensers of different capacitances, namely .0003, .0004 and .0005
mfd., and these are made to stand a potential of 7500 volts. The
condenser is therefore adjustable and, as you will see from the
picture B, it has one terminal wire at one end and three terminal
wires at the other end so that one, two or three condensers can be
used in series with the aerial. A condenser of this kind costs $5.40.
The Aerial Ammeter.--This is the same kind of a hot-wire ammeter
already described in connection with the experimental set, but it
reads to 5 amperes.
The Grid and Blocking Condensers.--Each of these is a fixed condenser
of .002 mfd. capacitance and is rated to stand 3,000 volts. It is
made like the aerial condenser but has only two terminals. It costs
$2.00.
The Key Circuit Apparatus.--This consists of: (1) the _grid leak_; (2)
the _chopper_; (3) the _choke coil_, and (4) the _key_. The grid leak
is connected in the lead from the grid to the aerial to keep the
voltage on the grid at the right potential. It has a resistance of
5000 ohms with a mid-tap at 2500 ohms as shown at C. It costs $2.00.
The chopper is simply a rotary interrupter driven by a small motor. It
comprises a wheel of insulating material in which 30 or more metal
segments are set in an insulating disk as shown at D. A metal contact
called a brush is fixed on either side of the wheel. It costs about
$7.00 and the motor to drive it is extra. The choke coil is wound up
of about 250 turns of No. 30 Brown and Sharpe gauge cotton covered
magnet wire on a spool which has a diameter of 2 inches and a length
of 3-1/4 inches.
The 5 Watt Oscillator Vacuum Tube.--This tube is made like the
amplifier tube described for use with the preceding experimental
transmitter, but it is larger, has a more perfect vacuum, and will
stand a plate potential of 350 volts while the plate current is .045
ampere. The filament takes a current of a little more than 2 amperes
at 7.5 volts. A standard 4-tap base is used with it. The tube costs
$8.00 and the porcelain base is $1.00 extra. It is shown at E.
The Storage Battery and Rheostat.--This must be a 5-cell battery so
that it will develop 10 volts. A storage battery of any capacity can
be used but the lowest priced one costs about $22.00. The rheostat for
regulating the battery current is the same as that used in the
preceding experimental transmitter.
The Filament Voltmeter.--To get the best results it is necessary that
the voltage of the current which heats the filament be kept at the
same value all of the time. For this transmitter a direct current
voltmeter reading from 0 to 15 volts is used. It is shown at F and
costs $7.50. The Oscillation Choke Coil.--This is made exactly like
the one described in connection with the experimental transmitter.
The Motor-Generator Set.--Where you have only a 110 or a 220 volt
direct current available as a source of power you need a
_motor-generator_ to change it to 350 volts, and this is an expensive
piece of apparatus. It consists of a single armature core with a motor
winding and a generator winding on it and each of these has its own
commutator. Where the low voltage current flows into one of the
windings it drives its as a motor and this in turn generates the
higher voltage current in the other winding. Get a 100 watt 350 volt
motor-generator; it is shown at F and costs about $75.00.
The Panel Cut-Out.--This switch and fuse block is the same as that
used in the experimental set.
The Protective Condenser.--This is a fixed condenser having a
capacitance of 1 mfd. and will stand 750 volts. It costs $2.00.
Connecting Up the Transmitting Apparatus.--From all that has gone
before you have seen that each piece of apparatus is fitted with
terminal, wires, taps or binding posts. To connect up the parts of
this transmitter it is only necessary to make the connections as shown
in the wiring diagram Fig. 78.
[Illustration: Fig. 78.--5 to 50 Watt C. W. Telegraph Transmitter.
(With Single Oscillation Tube.)]
A 200 Mile C. W. Telegraph Transmitter.--To make a continuous wave
telegraph transmitter that will cover distances up to 200 miles all
you have to do is to use two 5 watt vacuum tubes in _parallel_, all of
the rest of the apparatus being exactly the same. Connecting the
oscillator tubes up in parallel means that the two filaments are
connected across the leads of the storage battery, the two grids on
the same lead that goes to the aerial and the two plates on the same
lead that goes to the positive pole of the generator. Where two or
more oscillator tubes are used only one storage battery is needed, but
each filament must have its own rheostat. The wiring diagram Fig. 79
shows how the two tubes are connected up in parallel.
[Illustration: Fig. 79.--200 Mile C.W. Telegraph Transmitter (With Two
Tubes in Parallel.)]
A 500 Mile C. W. Telegraph Transmitter.--For sending to distances of
over 200 miles and up to 500 miles you can use either: (1) three or
four 5 watt oscillator tubes in parallel as described above, or (2)
one 50 watt oscillator tube. Much of the apparatus for a 50 watt tube
set is exactly the same as that used for the 5 watt sets. Some of the
parts, however, must be proportionately larger though the design all
the way through remains the same.
The Apparatus and Connections.--The aerial series condenser, the
blocking condenser, the grid condenser, the telegraph key, the
chopper, the choke coil in the key circuit, the filament voltmeter and
the protective condenser in the power circuit are identical with those
described for the 5 watt transmitting set.
The 50 Watt Vacuum Tube Oscillator.--This is the size of tube
generally used by amateurs for long distance continuous wave
telegraphy. A single tube will develop 2 to 3 amperes in your aerial.
The filament takes a 10 volt current and a plate potential of 1,000
volts is needed. One of these tubes is shown in Fig. 80 and the cost
is $30.00. A tube socket to fit it costs $2.50 extra.
[Illustration: Fig. 80.--50 Watt Oscillator Vacuum Tube.]
The Aerial Ammeter.--This should read to 5 amperes and the cost is
$6.25.
The Grid Leak Resistance.--It has the same resistance, namely 5,000
ohms as the one used with the 5 watt tube transmitter, but it is a
little larger. It is listed at $1.65.
The Oscillation Choke Coil.--The choke coil in the power circuit is
made of about 260 turns of No. 30 B. & S. cotton covered magnet wire
wound on a spool 2-1/4 inches in diameter and 3-1/4 inches long.
The Filament Rheostat.--This is made to take care of a 10 volt current
and it costs $10.00.
The Filament Storage Battery.--This must develop 12 volts and one
having an output of 40 ampere-hours costs about $25.00.
The Protective Condenser.--This condenser has a capacitance of 1 mfd.
and costs $2.00.
The Motor-Generator.--Where you use one 50 watt oscillator tube you
will need a motor-generator that develops a plate potential of 1000
volts and has an output of 200 watts. This machine will stand you
about $100.00.
The different pieces of apparatus for this set are connected up
exactly the same as shown in the wiring diagram in Fig. 78.
A 1000 Mile C. W. Telegraph Transmitter.--All of the parts of this
transmitting set are the same as for the 500 mile transmitter just
described except the motor generator and while this develops the same
plate potential, i.e., 1,000 volts, it must have an output of 500
watts; it will cost you in the neighborhood of $175.00. For this long
distance transmitter you use two 50 watt oscillator tubes in parallel
and all of the parts are connected together exactly the same as for
the 200 mile transmitter shown in the wiring diagram in Fig. 79.
CHAPTER XVII
CONTINUOUS WAVE TELEGRAPH TRANSMITTING SETS WITH ALTERNATING CURRENT
Within the last few years alternating current has largely taken the
place of direct current for light, heat and power purposes in and
around towns and cities and if you have alternating current service in
your home you can install a long distance continuous wave telegraph
transmitter with very little trouble and at a comparatively small
expense.
A 100 Mile C. W. Telegraph Transmitting Set.--The principal pieces of
apparatus for this transmitter are the same as those used for the _100
Mile Continuous Wave Telegraph Transmitting Set_ described and
pictured in the preceding chapter which used direct current, except
that an _alternating current power transformer_ is employed instead of
the more costly _motor-generator_.
The Apparatus Required.--The various pieces of apparatus you will need
for this transmitting set are: (1) one _hot-wire ammeter_ for the
aerial as shown at E in Fig. 75, but which reads to 5 amperes instead
of to 2.5 amperes; (2) one _tuning coil_ as shown at A in Fig. 77; (3)
one aerial condenser as shown at B in Fig. 77; (4) one _grid leak_ as
shown at C in Fig. 77; (5) one _telegraph key_ as shown at G in Fig.
75; (6) one _grid condenser_, made like the aerial condenser but
having only two terminals; (7) one _5 watt oscillator tube_ as shown
at E in Fig. 77; (8) one _.002 mfd. 3,000 volt by-pass condenser_,
made like the aerial and grid condensers; (9) one pair of _choke
coils_ for the high voltage secondary circuit; (10) one
_milli-ammeter_; (11) one A. C. _power transformer_; (12) one
_rheostat_ as shown at I in Fig. 75, and (13) one _panel cut-out_ as
shown at K in Fig. 75.
The Choke Coils.--Each of these is made by winding about 100 turns of
No. 28, Brown and Sharpe gauge, cotton covered magnet wire on a spool
2 inches in diameter and 2-1/2 inches long, when it will have an
inductance of about 0.5 _millihenry_ [Footnote: A millihenry is
1/1000th part of a henry.] at 1,000 cycles.
The Milli-ammeter.--This is an alternating current ammeter and reads
from 0 to 250 _milliamperes_; [Footnote: A _milliampere_ is the
1/1000th part of an ampere.] and is used for measuring the secondary
current that energizes the plate of the oscillator tube. It looks like
the aerial ammeter and costs about $7.50.
The A. C. Power Transformer.--Differing from the motor generator set
the power transformer has no moving parts. For this transmitting set
you need a transformer that has an input of 325 volts. It is made to
work on a 50 to 60 cycle current at 102.5 to 115 volts, which is the
range of voltage of the ordinary alternating lighting current. This
adjustment for voltage is made by means of taps brought out from the
primary coil to a rotary switch.
The high voltage secondary coil which energizes the plate has an
output of 175 watts and develops a potential of from 350 to 1,100
volts. The low voltage secondary coil which heats the filament has an
output of 175 watts and develops 7.5 volts. This transformer, which is
shown in Fig. 81, is large enough to take care of from one to four 5
watt oscillator tubes. It weighs about 15 pounds and sells for $25.00.
[Illustration: Fig. 81.--Alternation Current Power Transformer. (For
C. W. Telegraphy and Wireless Telephony.)]
[Illustration: The Transformer and Tuner of the World's Largest Radio
Station. Owned by the Radio Corporation of America at Rocky Point near
Port Jefferson L.I.]
Connecting Up the Apparatus.--The wiring diagram Fig. 82 shows clearly
how all of the connections are made. It will be observed that a
storage battery is not needed as the secondary coil of the transformer
supplies the current to heat the filament of the oscillator. The
filament voltmeter is connected across the filament secondary coil
terminals, while the plate milli-ammeter is connected to the mid-taps
of the plate secondary coil and the filament secondary coil.
[Illustration: Fig. 82. Wiring Diagram for 200 to 500 Mile C.W.
Telegraph Transmitting Set. (With Alternating Current)]
A 200 to 500 Mile C. W. Telegraph Transmitting Set.--Distances of from
200 to 500 miles can be successfully covered with a telegraph
transmitter using two, three or four 5 watt oscillator tubes in
parallel. The apparatus needed is identical with that used for the 100
mile transmitter just described. The tubes are connected in parallel
as shown in the wiring diagram in Fig. 83.
[Illustration: Fig. 83.--Wiring Diagram for 500 to 1000 Mile C. W.
Telegraph Transmitter.]
A 500 to 1,000 Mile C. W. Telegraph Transmitting Set.--With the
apparatus described for the above set and a single 50 watt oscillator
tube a distance of upwards of 500 miles can be covered, while with two
50 watt oscillator tubes in parallel you can cover a distance of 1,000
miles without difficulty, and nearly 2,000 miles have been covered
with this set.
The Apparatus Required.--All of the apparatus for this C. W.
telegraph transmitting set is the same as that described for the 100
and 200 mile sets but you will need: (1) one or two _50 watt
oscillator tubes with sockets;_ (2) one _key condenser_ that has a
capacitance of 1 mfd., and a rated potential of 1,750 volts; (3) one
_0 to 500 milli-ammeter_; (4) one _aerial ammeter_ reading to 5
amperes, and (5) an _A. C. power transformer_ for one or two 50 watt
tubes.
[Illustration: Broadcasting Government Reports by Wireless from
Washington. This shows Mr. Gale at work with his set in the Post
Office Department.]
The Alternating Current Power Transformer.--This power transformer is
made exactly like the one described in connection with the preceding
100 mile transmitter and pictured in Fig. 81, but it is considerably
larger. Like the smaller one, however, it is made to work with a 50 to
60 cycle current at 102.5 to 115 volts and, hence, can be used with
any A. C. lighting current.
It has an input of 750 volts and the high voltage secondary coil which
energizes the plate has an output of 450 watts and develops 1,500 to
3,000 volts. The low voltage secondary coil which heats the filament
develops 10.5 volts. This transformer will supply current for one or
two 50-watt oscillator tubes and it costs about $40.00.
Connecting Up the Apparatus.--Where a single oscillator tube is used
the parts are connected as shown in Fig. 82, and where two tubes are
connected in parallel the various pieces of apparatus are wired
together as shown in Fig. 83. The only difference between the 5 watt
tube transmitter and the 50 watt tube transmitter is in the size of
the apparatus with one exception; where one or two 50 watt tubes are
used a second condenser of large capacitance (1 mfd.) is placed in the
grid circuit and the telegraph key is shunted around it as shown in
the diagram Fig. 83.
CHAPTER XVIII
WIRELESS TELEPHONE TRANSMITTING SETS WITH DIRECT AND ALTERNATING
CURRENTS
In time past the most difficult of all electrical apparatus for the
amateur to make, install and work was the wireless telephone. This was
because it required a _direct current_ of not less than 500 volts to
set up the sustained oscillations and all ordinary direct current for
lighting purposes is usually generated at a potential of 110 volts.
Now as you know it is easy to _step-up_ a 110 volt alternating current
to any voltage you wish with a power transformer but until within
comparatively recent years an alternating current could not be used
for the production of sustained oscillations for the very good reason
that the state of the art had not advanced that far. In the new order
of things these difficulties have all but vanished and while a
wireless telephone transmitter still requires a high voltage direct
current to operate it this is easily obtained from 110 volt source of
alternating current by means of _vacuum tube rectifiers_.
The pulsating direct currents are then passed through a filtering
reactance coil, called a _reactor_, and one or more condensers, and
these smooth them out until they approximate a continuous direct
current. The latter is then made to flow through a vacuum tube
oscillator when it is converted into high frequency oscillations and
these are _varied_, or _modulated_, as it is called, by a _microphone
transmitter_ such as is used for ordinary wire telephony. The energy
of these sustained modulated oscillations is then radiated into space
from the aerial in the form of electric waves.
The distance that can be covered with a wireless telephone transmitter
is about one-fourth as great as that of a wireless telegraph
transmitter having the same input of initial current, but it is long
enough to satisfy the most enthusiastic amateur. For instance with a
wireless telephone transmitter where an amplifier tube is used to set
up the oscillations and which is made for a plate potential of 100
volts, distances up to 10 or 15 miles can be covered.
With a single 5 watt oscillator tube energized by a direct current of
350 volts from either a motor-generator or from a power transformer
(after it has been rectified and smoothed out) speech and music can be
transmitted to upwards of 25 miles. Where two 5 watt tubes connected
in parallel are used wireless telephone messages can be transmitted to
distances of 40 or 50 miles. Further, a single 50 watt oscillator tube
will send to distances of 50 to 100 miles while two of these tubes in
parallel will send from 100 to 200 miles. Finally, where four or five
oscillator tubes are connected in parallel proportionately greater
distances can be covered.
A Short Distance Wireless Telephone Transmitting Set-With 110 Volt
Direct Lighting Current.--For this very simple, short distance
wireless telephone transmitting set you need the same apparatus as
that described and pictured in the beginning of Chapter XVI for a
_Short Distance C. W. Telegraph Transmitter_, except that you use a
_microphone transmitter_ instead of a _telegraph key_. If you have a
110 volt direct lighting current in your home you can put up this
short distance set for very little money and it will be well worth
your while to do so.
The Apparatus You Need.--For this set you require: (1) one _tuning
coil_ as shown at A and B in Fig. 75; (2) one _aerial ammeter_ as
shown at C in Fig. 75; (3) one _aerial condenser_ as shown at C in
Fig. 75; (4) one _grid, blocking and protective condenser_ as shown at
D in Fig. 75; (5) one _grid leak_ as shown at C in Fig. 77; (6) one
_vacuum tube amplifier_ which is used as an _oscillator_; (7) one _6
volt storage battery_; (8) one _rheostat_ as shown at I in Fig. 75;
(9) one _oscillation choke coil_; (10) one _panel cut-out_ as shown at
K in Fig. 75 and an ordinary _microphone transmitter_.
The Microphone Transmitter.--The best kind of a microphone to use with
this and other telephone transmitting sets is a _Western Electric No.
284-W_. [Footnote: Made by the Western Electric Company, Chicago,
Ill.] This is known as a solid back transmitter and is the standard
commercial type used on all long distance Bell telephone lines. It
articulates sharply and distinctly and there are no current variations
to distort the wave form of the voice and it will not buzz or sizzle.
It is shown in Fig. 84 and costs $2.00. Any other good microphone
transmitter can be used if desired.
[Illustration: Fig. 84.--Standard Microphone Transmitter.]
Connecting Up the Apparatus.--Begin by connecting the leading-in wire
with one of the terminals of the microphone transmitter, as shown in
the wiring diagram Fig. 85, and the other terminal of this to one end
of the tuning coil. Now connect _clip 1_ of the tuning coil to one of
the posts of the hot-wire ammeter, the other post of this to one end
of aerial condenser and, finally, the other end of the latter with the
water pipe or other ground. The microphone can be connected in the
ground wire and the ammeter in the aerial wire and the results will be
practically the same.
[Illustration: Fig. 85.--Wiring Diagram of Short Distance Wireless
Telephone Set. (Microphone in Aerial Wire.)]
Next connect one end of the grid condenser to the post of the tuning
coil that makes connection with the microphone and the other end to
the grid of the tube, and then shunt the grid leak around the
condenser. Connect the + or _positive_ electrode of the storage
battery with one terminal of the filament of the vacuum tube, the
other terminal of the filament with one post of the rheostat and the
other post of this with the - or _negative_ electrode of the battery.
This done, connect _clip 2_ of the tuning coil to the + or _positive_
electrode of the battery and bring a lead from it to one of the switch
taps of the panel cut-out.
Now connect _clip 3_ of the tuning coil with one end of the blocking
condenser, the other end of this with one terminal of the choke coil
and the other terminal of the latter with the other switch tap of the
cut-out. Connect the protective condenser across the direct current
feed wires between the panel cut-out and the choke coil. Finally
connect the ends of a lamp cord to the fuse socket taps of the
cut-out, and connect the other ends to a lamp plug and screw it into
the lamp socket of the feed wires. Screw in a pair of 5 ampere _fuse
plugs_, close the switch and you are ready to tune the transmitter and
talk to your friends.
A 25 to 50 Mile Wireless Telephone Transmitter--With Direct Current
Motor Generator.--Where you have to start with 110 or 220 volt direct
current and you want to transmit to a distance of 25 miles or more you
will have to install a _motor-generator_. To make this transmitter you
will need exactly the same apparatus as that described and pictured
for the _100 Mile C. W. Telegraph Transmitting Set_ in Chapter XVI,
except that you must substitute a _microphone transmitter_ and a
_telephone induction coil_, or a _microphone transformer_, or still
better, a _magnetic modulator_, for the telegraph key and chopper.
The Apparatus You Need.--To reiterate; the pieces of apparatus you
need are: (1) one _aerial ammeter_ as shown at E in Fig. 75; (2) one
_tuning coil_ as shown at A in Fig. 77; (3) one _aerial condenser_ as
shown at B in Fig. 77; (4) one _grid leak_ as shown at C in Fig. 77;
(5) one _grid, blocking_ and _protective condenser_; (6) one _5 watt
oscillator tube_ as shown at E in Fig. 77; (7) one _rheostat_ as shown
at I in Fig. 75; (8) one _10 volt (5 cell) storage battery_; (9) one
_choke coil_; (10) one _panel cut-out_ as shown at K in Fig. 75, and
(11) a _motor-generator_ having an input of 110 or 220 volts and an
output of 350 volts.
In addition to the above apparatus you will need: (12) a _microphone
transmitter_ as shown in Fig. 84; (13) a battery of four dry cells or
a 6 volt storage battery, and either (14) a _telephone induction coil_
as shown in Fig. 86; (15) a _microphone transformer_ as shown in Fig.
87; or a _magnetic modulator_ as shown in Fig. 88. All of these parts
have been described, as said above, in Chapter XVI, except the
microphone modulators.
[Illustration: Fig. 86.--Telephone Induction Coil. (Used with
Microphone Transmitter.)]
[Illustration: Fig. 87.--Microphone Transformer. (Used with Microphone
Transmitter.)]
[Illustration: Fig. 88.--Magnetic Modulator. (Used with Microphone
Transmitter.)]
The Telephone Induction Coil.--This is a little induction coil that
transforms the 6-volt battery current after it has flowed through and
been modulated by the microphone transmitter into alternating currents
that have a potential of 1,000 volts of more. It consists of a primary
coil of _No. 20 B. and S._ gauge cotton covered magnet wire wound on a
core of soft iron wires while around the primary coil is wound a
secondary coil of _No. 30_ magnet wire. Get a _standard telephone
induction coil_ that has a resistance of 500 or 750 ohms and this will
cost you a couple of dollars.
The Microphone Transformer.--This device is built on exactly the same
principle as the telephone induction coil just described but it is
more effective because it is designed especially for modulating the
oscillations set up by vacuum tube transmitters. As with the telephone
induction coil, the microphone transmitter is connected in series with
the primary coil and a 6 volt dry or storage battery.
In the better makes of microphone transformer, there is a third
winding, called a _side tone_ coil, to which a headphone can be
connected so that the operator who is speaking into the microphone can
listen-in and so learn if his transmitter is working up to standard.
The Magnetic Modulator.--This is a small closed iron core transformer
of peculiar design and having a primary and a secondary coil wound on
it. This device is used to control the variations of the oscillating
currents that are set up by the oscillator tube. It is made in three
sizes and for the transmitter here described you want the smallest
size, which has an output of 1/2 to 1-1/2 amperes. It costs about
$10.00.
How the Apparatus Is Connected Up.--The different pieces of apparatus
are connected together in exactly the same way as the _100 Mile C. W.
Telegraph Set_ in Chapter XVI except that the microphone transmitter
and microphone modulator (whichever kind you use) is substituted for
the telegraph key and chopper.
Now there are three different ways that the microphone and its
modulator can be connected in circuit. Two of the best ways are shown
at A and B in Fig. 89. In the first way the secondary terminals of the
modulator are shunted around the grid leak in the grid circuit as at
A, and in the second the secondary terminals are connected in the
aerial as at B. Where an induction coil or a microphone transformer is
used they are shunted around a condenser, but this is not necessary
with the magnetic modulator. Where a second tube is used as in Fig. 90
then the microphone and its modulator are connected with the grid
circuit and _clip 3_ of the tuning coil.
[Illustration: Fig. 89.--Wiring Diagram of 25 to 50 Mile Wireless
Telephone. (Microphone Modulator Shunted Around Grid-Leak Condenser.)]
[Illustration: (B) Fig. 89.--Microphone Modulator Connected in Aerial
Wire.]
[Illustration: Fig. 90.--Wiring Diagram of 50 to 100 Mile Wireless
Telephone Transmitting Set.]
A 50 to 100 Mile Wireless Telephone Transmitter--With Direct Current
Motor Generator.--As the initial source of current available is taken
to be a 110 or 220 volt direct current a motor-generator having an
output of 350 volts must be used as before. The only difference
between this transmitter and the preceding one is that: (1) two 5 watt
tubes are used, the first serving as an _oscillator_ and the second as
a _modulator_; (2) an _oscillation choke coil_ is used in the plate
circuit; (3) a _reactance coil_ or _reactor_, is used in the plate
circuit; and (4) a _reactor_ is used in the grid circuit.
The Oscillation Choke Coil.--You can make this choke coil by winding
about 275 turns of _No. 28 B. and S. gauge_ cotton covered magnet wire
on a spool 2 inches in diameter and 4 inches long. Give it a good
coat of shellac varnish and let it dry thoroughly.
The Plate and Grid Circuit Reactance Coils.--Where a single tube is
used as an oscillator and a second tube is employed as a modulator, a
_reactor_, which is a coil of wire wound on an iron core, is used in
the plate circuit to keep the high voltage direct current of the
motor-generator the same at all times. Likewise the grid circuit
reactor is used to keep the voltage of the grid at a constant value.
These reactors are made alike and a picture of one of them is shown in
Fig. 91 and each one will cost you $5.75.
[Illustration: Fig. 91.--Plate and Grid Circuit Reactor.]
Connecting up the Apparatus.--All of the different pieces of apparatus
are connected up as shown in Fig. 89. One of the ends of the secondary
of the induction coil, or the microphone transformer, or the magnetic
modulator is connected to the grid circuit and the other end to _clip
3_ of the tuning coil.
A 100 to 200 Mile Wireless Telephone Transmitter--With Direct Current
Motor Generator.--By using the same connections shown in the wiring
diagrams in Fig. 89 and a single 50 watt oscillator tube your
transmitter will then have a range of 100 miles or so, while if you
connect up the apparatus as shown in Fig. 90 and use two 50 watt tubes
you can work up to 200 miles. Much of the apparatus for a 50 watt
oscillator set where either one or two tubes are used is of the same
size and design as that just described for the 5 watt oscillator sets,
but, as in the C. W. telegraph sets, some of the parts must be
proportionately larger. The required parts are (1) the _50 watt tube_;
(2) the _grid leak resistance_; (3) the _filament rheostat_; (4) the
_filament storage battery_; and (5) the _magnetic modulator_. All of
these parts, except the latter, are described in detail under the
heading of a _500 Mile C. W. Telegraph Transmitting Set_ in Chapter
XVI, and are also pictured in that chapter.
It is not advisable to use an induction coil for the modulator for
this set, but use, instead, either a telephone transformer, or better,
a magnetic modulator of the second size which has an output of from
1-1/2 to 3-1/2 amperes. The magnetic modulator is described and
pictured in this chapter.
A 50 to 100 Mile Wireless Telephone Transmitting Set--With 110 Volt
Alternating Current.--If you have a 110 volt [Footnote: Alternating
current for lighting purposes ranges from 102.5 volts to 115 volts, so
we take the median and call it 110 volts.] alternating current
available you can use it for the initial source of energy for your
wireless telephone transmitter. The chief difference between a
wireless telephone transmitting set that uses an alternating current
and one that uses a direct current is that: (1) a _power transformer_
is used for stepping up the voltage instead of a motor-generator, and
(2) a _vacuum tube rectifier_ must be used to convert the alternating
current into direct current.
The Apparatus You Need.--For this telephone transmitting set you need:
(1) one _aerial ammeter_; (2) one _tuning coil_; (3) one _telephone
modulator_; (4) one _aerial series condenser_; (5) one _4 cell dry
battery_ or a 6 volt storage battery; (6) one _microphone
transmitter_; (7) one _battery switch_; (8) one _grid condenser_; (9)
one _grid leak_; (10) two _5 watt oscillator tubes with sockets_; (11)
one _blocking condenser_; (12) one _oscillation choke coil_; (13) two
_filter condensers_; (14) one _filter reactance coil_; (15) an
_alternating current power transformer_, and (16) two _20 watt
rectifier vacuum tubes_.
All of the above pieces of apparatus are the same as those described
for the _100 Mile C. W. Telegraph Transmitter_ in Chapter XVII,
except: (a) the _microphone modulator_; (b) the _microphone
transmitter_ and (c) the _dry_ or _storage battery_, all of which are
described in this chapter; and the new parts which are: (d) the
_rectifier vacuum tubes_; (e) the _filter condensers_; and (f) the
_filter reactance coil_; further and finally, the power transformer
has a _third_ secondary coil on it and it is this that feeds the
alternating current to the rectifier tubes, which in turn converts it
into a pulsating direct current.
The Vacuum Tube Rectifier.--This rectifier has two electrodes, that
is, it has a filament and a plate like the original vacuum tube
detector, The smallest size rectifier tube requires a plate potential
of 550 volts which is developed by one of the secondary coils of the
power transformer. The filament terminal takes a current of 7.5 volts
and this is supplied by another secondary coil of the transformer.
This rectifier tube delivers a direct current of 20 watts at 350
volts. It looks exactly like the 5 watt oscillator tube which is
pictured at E in Fig. 77. The price is $7.50.
The Filter Condensers.--These condensers are used in connection with
the reactance coil to smooth out the pulsating direct current after it
has passed through the rectifier tube. They have a capacitance of 1
mfd. and will stand 750 volts. These condensers cost about $2.00 each.
The Filter Reactance Coil.--This reactor which is shown in Fig. 92,
has about the same appearance as the power transformer but it is
somewhat smaller. It consists of a coil of wire wound on a soft iron
core and has a large inductance, hence the capacitance of the filter
condensers are proportionately smaller than where a small inductance
is used which has been the general practice. The size you require for
this set has an output of 160 milliamperes and it will supply current
for one to four 5 watt oscillator tubes. This size of reactor costs
$11.50.
[Illustration: Fig. 92.--Filter Reactor for Smoothing out Rectified
Currents.]
Connecting Up the Apparatus.--The wiring diagram in Fig. 93 shows how
the various pieces of apparatus for this telephone transmitter are
connected up. You will observe: (1) that the terminals of the power
transformer secondary coil which develops 10 volts are connected to
the filaments of the oscillator tubes; (2) that the terminals of the
other secondary coil which develops 10 volts are connected with the
filaments of the rectifier tubes; (3) that the terminals of the third
secondary coil which develops 550 volts are connected with the plates
of the rectifier tubes; (4) that the pair of filter condensers are
connected in parallel and these are connected to the mid-taps of the
two filament secondary coils; (5) that the reactance coil and the
third filter condenser are connected together in series and these are
shunted across the filter condensers, which are in parallel; and,
finally, (6) a lead connects the mid-tap of the 550-volt secondary
coil of the power transformer with the connection between the reactor
and the third filter condenser.
[Illustration: Fig 93.--100 to 200 Mile Wireless Telephone
Transmitter.]
A 100 to 200 Mile Wireless Telephone Transmitting Set--With 110 Volt
Alternating Current.--This telephone transmitter is built up of
exactly the same pieces of apparatus and connected up in precisely the
same way as the one just described and shown in Fig. 93.
Apparatus Required.--The only differences between this and the
preceding transmitter are: (1) the _magnetic modulator_, if you use
one, should have an output of 3-1/2 to 5 amperes; (2) you will need
two _50 watt oscillator tubes with sockets_; (3) two _150 watt
rectifier tubes with sockets_; (4) an _aerial ammeter_ that reads to
_5 amperes_; (5) three _1 mfd. filter condensers_ in parallel; (6)
_two filter condensers of 1 mfd. capacitance_ that will stand _1750
volts_; and (6) a _300 milliampere filter reactor_.
The apparatus is wired up as shown in Fig. 93.
CHAPTER XIX
THE OPERATION OF VACUUM TUBE TRANSMITTERS
The three foregoing chapters explained in detail the design and
construction of (1) two kinds of C. W. telegraph transmitters, and (2)
two kinds of wireless telephone transmitters, the difference between
them being whether they used (A) a direct current, or (B) an
alternating current as the initial source of energy. Of course there
are other differences between those of like types as, for instance,
the apparatus and connections used (_a_) in the key circuits, and
(_b_) in the microphone circuits. But in all of the transmitters
described of whatever type or kind the same fundamental device is used
for setting up sustained oscillations and this is the _vacuum tube_.
The Operation of the Vacuum Tube Oscillator.--The operation of the
vacuum tube in producing sustained oscillations depends on (1) the
action of the tube as a valve in setting up the oscillations in the
first place and (2) the action of the grid in amplifying the
oscillations thus set up, both of which we explained in Chapter XIV.
In that chapter it was also pointed out that a very small change in
the grid potential causes a corresponding and larger change in the
amount of current flowing from the plate to the filament; and that if
a vacuum tube is used for the production of oscillations the initial
source of current must have a high voltage, in fact the higher the
plate voltage the more powerful will be the oscillations.
To understand how oscillations are set up by a vacuum tube when a
direct current is applied to it, take a look at the simple circuits
shown in Fig. 94. Now when you close the switch the voltage from the
battery charges the condenser and keeps it charged until you open it
again; the instant you do this the condenser discharges through the
circuit which includes it and the inductance coil, and the discharge
of a condenser is always oscillatory.
[Illustration: (A) and (B) Fig. 94. Operation of Vacuum Tube
Oscillators.]
Where an oscillator tube is included in the circuits as shown at A and
B in Fig. 94, the grid takes the place of the switch and any slight
change in the voltage of either the grid or the plate is sufficient to
start a train of oscillations going. As these oscillations surge
through the tube the positive parts of them flow from the plate to the
filament and these carry more of the direct current with them.
To make a tube set up powerful oscillations then, it is only necessary
that an oscillation circuit shall be provided which will feed part of
the oscillations set up by the tube back to the grid circuit and when
this is done the oscillations will keep on being amplified until the
tube reaches the limit of its output.
[Illustration: (C) Fig. 94.--How a Direct Current Sets up
Oscillations.]
The Operation of C. W. Telegraph Transmitters With Direct
Current--Short Distance C. W. Transmitter.--In the transmitter shown
in the wiring diagram in Fig. 76 the positive part of the 110 volt
direct current is carried down from the lamp socket through one side
of the panel cut-out, thence through the choke coil and to the plate
of the oscillator tube, when the latter is charged to the positive
sign. The negative part of the 110 volt direct current then flows down
the other wire to the filament so that there is a difference of
potential between the plate and the filament of 110 volts. Now when
the 6-volt battery current is switched on the filament is heated to
brilliancy, and the electrons thrown off by it form a conducting path
between it and the plate; the 110 volt current then flows from the
latter to the former.
Now follow the wiring from the plate over to the blocking condenser,
thence to _clip 3_ of the tuning coil, through the turns of the latter
to _clip 2_ and over to the filament and, when the latter is heated,
you have a _closed oscillation circuit_. The oscillations surging in
the latter set up other and like oscillations in the tuning coil
between the end of which is connected with the grid, the aerial and
the _clip 2_, and these surge through the circuit formed by this
portion of the coil, the grid condenser and the filament; this is the
amplifying circuit and it corresponds to the regenerative circuit of a
receiving set.
When oscillations are set up in it the grid is alternately charged to
the positive and negative signs. These reversals of voltage set up
stronger and ever stronger oscillations in the plate circuit as before
explained. Not only do the oscillations surge in the closed circuits
but they run to and fro on the aerial wire when their energy is
radiated in the form of electric waves. The oscillations are varied by
means of the telegraph key which is placed in the grid circuit as
shown in Fig. 76.
The Operation of the Key Circuit.--The effect in a C. W. transmitter
when a telegraph key is connected in series with a buzzer and a
battery and these are shunted around the condenser in the grid
circuit, is to rapidly change the wave form of the sustained
oscillations, and hence, the length of the waves that are sent out.
While no sound can be heard in the headphones at the receiving station
so long as the points of the key are not in contact, when they are in
contact the oscillations are modulated and sounds are heard in the
headphones that correspond to the frequency of the buzzer in the key
circuit.
The Operation of C. W. Telegraph Transmitters with Direct
Current.--The chief differences between the long distance sets which
use a direct current, i.e., those described in Chapter XVI, and the
short distance transmitting sets are that the former use: (1) a
motor-generator set for changing the low voltage direct current into
high voltage direct current, and (2) a chopper in the key circuit. The
way the motor-generator changes the low- into high-voltage current has
been explained in Chapter XVI.
The chopper interrupts the oscillations surging through the grid
circuit at a frequency that the ear can hear, that is to say, about
800 to 1,000 times per second. When the key is open, of course, the
sustained oscillations set up in the circuits will send out continuous
waves but when the key is closed these oscillations are broken up and
then they send out discontinuous waves. If a heterodyne receiving set,
see Chapter XV, is being used at the other end you can dispense with
the chopper and the key circuit needed is very much simplified. The
operation of key circuits of the latter kind will be described
presently.
The Operation of C. W. Telegraph Transmitters with Alternating
Current--With a Single Oscillator Tube.--Where an oscillator tube
telegraph transmitter is operated by a 110 volt alternating current as
the initial source of energy, a buzzer, chopper or other interruptor
is not needed in the key circuit. This is because oscillations are set
up only when the plate is energized with the positive part of the
alternating current and this produces an intermittent musical tone in
the headphones. Hence this kind of a sending set is called a _tone
transmitter_.
Since oscillations are set up only by the positive part or voltage of
an alternating current it is clear that, as a matter of fact, this
kind of a transmitter does not send out continuous waves and therefore
it is not a C. W. transmitter. This is graphically shown by the curve
of the wave form of the alternating current and the oscillations that
are set up by the positive part of it in Fig. 95. Whenever the
positive half of the alternating current energizes the plate then
oscillations are set up by the tube and, conversely, when the negative
half of the current charges the plate no oscillations are produced.
[Illustration: Fig. 95.--Positive Voltage only sets up Oscillations.]
You will also observe that the oscillations set up by the positive
part of the current are not of constant amplitude but start at zero
the instant the positive part begins to energize the plate and they
keep on increasing in amplitude as the current rises in voltage until
the latter reaches its maximum; then as it gradually drops again to
zero the oscillations decrease proportionately in amplitude with it.
Heating the Filament with Alternating Current.--Where an alternating
current power transformer is used to develop the necessary plate
voltage a second secondary coil is generally provided for heating the
filament of the oscillation tube. This is better than a direct current
for it adds to the life of the filament. When you use an alternating
current to heat the filament keep it at the same voltage rather than
at the same amperage (current strength). To do this you need only to
use a voltmeter across the filament terminals instead of an ammeter in
series with it; then regulate the voltage of the filament with a
rheostat.
The Operation of C. W. Telegraph Transmitters with Alternating
Current--With Two Oscillator Tubes.--By using two oscillator tubes and
connecting them up with the power transformer and oscillating circuits
as shown in the wiring diagram in Fig. 83 the plates are positively
energized alternately with every reversal of the current and,
consequently, there is no time period between the ending of the
oscillations set up by one tube and the beginning of the oscillations
set up by the other tube. In other words these oscillations are
sustained but as in the case of those of a single tube, their
amplitude rises and falls. This kind of a set is called a _full wave
rectification transmitter_.
The waves radiated by this transmitter can be received by either a
crystal detector or a plain vacuum-tube detector but the heterodyne
receptor will give you better results than either of the foregoing
types.
The Operation of Wireless Telephone Transmitters with Direct
Current--Short Distance Transmitter.--The operation of this short
distance wireless telephone transmitter, a wiring diagram of which is
shown in Fig. 85 is exactly the same as that of the _Direct Current
Short Distance C. W. Telegraph Transmitter_ already explained in this
chapter. The only difference in the operation of these sets is the
substitution of the _microphone transmitter_ for the telegraph key.
The Microphone Transmitter.--The microphone transmitter that is used
to vary, or modulate, the sustained oscillations set up by the
oscillator tube and circuits is shown in Fig. 84. By referring to the
diagram at A in this figure you will readily understand how it
operates. When you speak into the mouthpiece the _sound waves_, which
are waves in the air, impinge upon the diaphragm and these set it into
vibration--that is, they make it move to and fro.
When the diaphragm moves toward the back of the transmitter it forces
the carbon granules that are in the cup closer together; this lowers
their resistance and allows more current from the battery to flow
through them; when the pressure of the air waves is removed from the
diaphragm it springs back toward the mouth-piece and the carbon
granules loosen up when the resistance offered by them is increased
and less current can flow through them. Where the oscillation current
in the aerial wire is small the transmitter can be connected directly
in series with the latter when the former will surge through it. As
you speak into the microphone transmitter its resistance is varied and
the current strength of the oscillations is varied accordingly.
The Operation of Wireless Telephone Transmitters with Direct
Current--Long Distance Transmitters.--In the wireless telephone
transmitters for long distance work which were shown and described in
the preceding chapter a battery is used to energize the microphone
transmitter, and these two elements are connected in series with a
_microphone modulator_. This latter device may be either (1) a
_telephone induction coil_, (2) a _microphone transformer_, or (3) a
_magnetic modulator_; the first two of these devices step-up the
voltage of the battery current and the amplified voltage thus
developed is impressed on the oscillations that surge through the
closed oscillation circuit or the aerial wire system according to the
place where you connect it. The third device works on a different
principle and this will be described a little farther along.
The Operation of Microphone Modulators--The Induction Coil.--This
device is really a miniature transformer, see A in Fig. 86, and its
purpose is to change the 6 volt direct current that flows through the
microphone into 100 volts alternating current; in turn, this is
impressed on the oscillations that are surging in either (1) the grid
circuit as shown at A in Fig. 89, and in Fig. 90, (2) the aerial wire
system, as shown at B in Fig. 89 and Fig. 93. When the current from
the battery flows through the primary coil it magnetizes the soft iron
core and as the microphone varies the strength of the current the high
voltage alternating currents set up in the secondary coil of the
induction coil are likewise varied, when they are impressed upon and
modulate the oscillating currents.
The Microphone Transformer.--This is an induction coil that is
designed especially for wireless telephone modulation. The iron core
of this transformer is also of the open magnetic circuit type, see A
in Fig. 87, and the _ratio_ of the turns [Footnote: See Chapter VI] of
the primary and the secondary coil is such that when the secondary
current is impressed upon either the grid circuit or the aerial wire
system it controls the oscillations flowing through it with the
greatest efficiency.
The Magnetic Modulator.--This piece of apparatus is also called a
_magnetic amplifier_. The iron core is formed of very thin plates, or
_laminations_ as they are called, and this permits high-frequency
oscillations to surge in a coil wound on it. In this transformer, see
A in Fig. 88, the current flowing through the microphone varies the
magnetic permeability of the soft iron core by the magnetic saturation
of the latter. Since the microphone current is absolutely distinct
from the oscillating currents surging through the coil of the
transformer a very small direct current flowing through a coil on the
latter will vary or modulate very large oscillating currents surging
through the former. It is shown connected in the aerial wire system
at A in Fig. 88, and in Fig. 93.
Operation of the Vacuum Tube as a Modulator.--Where a microphone
modulator of the induction coil or microphone transformer type is
connected in the grid circuit or aerial wire system the modulation is
not very effective, but by using a second tube as a _modulator_, as
shown in Fig. 90, an efficient degree of modulation can be had. Now
there are two methods by which a vacuum tube can be used as a
modulator and these are: (1) by the _absorption_ of the energy of the
current set up by the oscillator tube, and (2) by _varying_ the direct
current that energizes the plate of the oscillator tube.
The first of these two methods is not used because it absorbs the
energy of the oscillating current produced by the tube and it is
therefore wasteful. The second method is an efficient one, as the
direct current is varied before it passes into the oscillator tube.
This is sufficient reason for describing only the second method. The
voltage of the grid of the modulator tube is varied by the secondary
coil of the induction coil or microphone transformer, above described.
In this way the modulator tube acts like a variable resistance but it
amplifies the variations impressed on the oscillations set up by the
oscillator tube. As the magnetic modulator does the same thing a
vacuum tube used as a modulator is not needed where the former is
employed. For this reason a magnetic modulator is the cheapest in the
long run.
The Operation of Wireless Telephone Transmitters with Alternating
Current.--Where an initial alternating current is used for wireless
telephony, the current must be rectified first and then smoothed out
before passing into the oscillator tube to be converted into
oscillations. Further so that the oscillations will be sustained, two
oscillator tubes must be used, and, finally, in order that the
oscillations may not vary in amplitude the alternating current must be
first changed into direct current by a pair of rectifier vacuum tubes,
as shown in Fig. 93. When this is done the plates will be positively
charged alternately with every reversal of the current in which case
there will be no break in the continuity of the oscillations set up
and therefore in the waves that are sent out.
The Operation of Rectifier Vacuum Tubes.--The vacuum tube rectifier is
simply a two electrode vacuum tube. The way in which it changes a
commercial alternating current into pulsating direct current is the
same as that in which a two electrode vacuum tube detector changes an
oscillating current into pulsating direct currents and this has been
explained in detail under the heading of _The Operation of a Two
Electrode Vacuum Tube Detector_ in Chapter XII. In the _C. W.
Telegraph Transmitting Sets_ described in Chapter XVII, the oscillator
tubes act as rectifiers as well as oscillators but for wireless
telephony the alternating current must be rectified first so that a
continuous direct current will result.
The Operation of Reactors and Condensers.--A reactor is a single coil
of wire wound on an iron core, see Fig. 90 and A in Fig. 91, and it
should preferably have a large inductance. The reactor for the plate
and grid circuit of a wireless telephone transmitter where one or more
tubes are used as modulators as shown in the wiring diagram in Fig.
90, and the filter reactor shown in Fig. 92, operate in the same way.
When an alternating current flows through a coil of wire the reversals
of the current set up a _counter electromotive force_ in it which
opposes, that is _reacts_, on the current, and the _higher_ the
frequency of the current the _greater_ will be the _reactance_. When
the positive half of an alternating current is made to flow through a
large resistance the current is smoothed out but at the same time a
large amount of its energy is used up in producing heat.
But when the positive half of an alternating current is made to flow
through a large inductance it acts like a large resistance as before
and likewise smooths out the current, but none of its energy is wasted
in heat and so a coil having a large inductance, which is called an
_inductive reactance_, or just _reactor_ for short, is used to smooth
out, or filter, the alternating current after it has been changed into
a pulsating direct current by the rectifier tubes.
A condenser also has a reactance effect on an alternating current but
different from an induction coil the _lower_ the frequency the
_greater_ will be the reactance. For this reason both a filter reactor
and _filter condensers_ are used to smooth out the pulsating direct
currents.
CHAPTER XX
HOW TO MAKE A RECEIVING SET FOR $5.00 OR LESS
In the chapters on _Receptors_ you have been told how to build up
high-grade sets. But there are thousands of boys, and, probably, not a
few men, who cannot afford to invest $25.00, more or less, in a
receiving set and would like to experiment in a small way.
The following set is inexpensive, and with this cheap, little portable
receptor you can get the Morse code from stations a hundred miles
distant and messages and music from broadcasting stations if you do
not live too far away from them. All you need for this set are: (1) a
_crystal detector_, (2) a _tuning coil_ and (3) an _earphone_. You can
make a crystal detector out of a couple of binding posts, a bit of
galena and a piece of brass wire, or, better, you can buy one all
ready to use for 50 cents.
[Illustration: Wireless Receptor, the size of a Safety Match Box. A
Youthful Genius in the person of Kenneth R. Hinman, Who is only twelve
years old, has made a Wireless Receiving Set that fits neatly into a
Safety Match Box. With this Instrument and a Pair of Ordinary
Receivers, He is able to catch not only Code Messages but the regular
Broadcasting Programs from Stations Twenty and Thirty Miles Distant.]
The Crystal Detector.--This is known as the _Rasco baby_ detector and
it is made and sold by the _Radio Specialty Company_, 96 Park Place,
New York City. It is shown in Fig. 96. The base is made of black
composition and on it is mounted a standard in which a rod slides and
on one end of this there is fixed a hard rubber adjusting knob while
the other end carries a thin piece of _phosphor-bronze wire_, called a
_cat-whisker_. To secure the galena crystal in the cup you simply
unscrew the knurled cap, place it in the cavity of the post and screw
the cap back on again. The free end of the cat-whisker wire is then
adjusted so that it will rest lightly on the exposed part of the
galena.
[Illustration: Fig. 96.--Rasco Baby Crystal Detector.]
The Tuning Coil.--You will have to make this tuning coil, which you
can do at a cost of less than $1.00, as the cheapest tuning coil you
can buy costs at least $3.00, and we need the rest of our $5.00 to
invest in the earphone. Get a cardboard tube, such as is used for
mailing purposes, 2 inches in diameter and 3 inches long, see A in
Fig. 97. Now wind on 250 turns of _No. 40 Brown and Sharpe gauge plain
enameled magnet wire_. You can use _No. 40 double cotton covered
magnet wire_, in which case you will have to shellac the tube and the
wire after you get it on.
[Illustration: Fig. 97.--How the Tuning Coil is Made.]
As you wind on the wire take off a tap at every 15th turn, that is,
scrape the wire and solder on a piece about 7 inches long, as shown in
Fig. 99; and do this until you have 6 taps taken off. Instead of
leaving the wires outside of the tube bring them to the inside of it
and then out through one of the open ends. Now buy a _round wood-base
switch_ with 7 contact points on it as shown at B in Fig. 97. This
will cost you 25 or 50 cents.
The Headphone.--An ordinary Bell telephone receiver is of small use
for wireless work as it is wound to too low a resistance and the
diaphragm is much too thick. If you happen to have a Bell phone you
can rewind it with _No. 40_ single covered silk magnet wire, or
enameled wire of the same size, when its sensitivity will be very
greatly improved. Then you must get a thin diaphragm and this should
_not_ be enameled, as this tends to dampen the vibrations of it. You
can get a diaphragm of the right kind for 5 cents.
The better way, though, is to buy an earphone made especially for
wireless work. You can get one wound to 1000 ohms resistance for $1.75
and this price includes a cord. [Footnote: This is Mesco, No. 470
wireless phone. Sold by the Manhattan Electrical Supply Co., Park
Place, N.Y.C.] For $1.00 extra you can get a head-band for it, and
then your phone will look like the one pictured in Fig. 98.
[Illustration: Fig. 98.--Mesco 1000 Ohm Head Set.]
How to Mount the Parts.--Now mount the coil on a wood base, 1/2 or 1
inch thick, 3-1/2 inches wide and 5-1/2 inches long, and then connect
one end of the coil to one of the end points on the switch, and
connect each succeeding tap to one of the switch points, as shown
schematically in Fig. 99 and diagrammatically in Fig. 100. This done,
screw the switch down to the base. Finally screw the detector to the
base and screw two binding posts in front of the coil. These are for
the earphone.
[Illustration: Fig. 99.--Schematic Layout of $5.00 Receiving Set.]
[Illustration: Fig. 100.--Wiring Diagram for $5.00 Receiving Set.]
The Condenser.--You do not have to connect a condenser across the
earphone but if you do you will improve the receiving qualities of the
receptor.
How to Connect Up the Receptor.--Now connect up all the parts as shown
in Figs. 99 and 100, then connect the leading-in wire of the aerial
with the lever of the switch; and connect the free end of the tuning
coil with the _ground_. If you have no aerial wire try hooking it up
to a rain pipe that is _not grounded_ or the steel frame of an
umbrella. For a _ground_ you can use a water pipe, an iron pipe driven
into the ground, or a hydrant. Put on your headphone, adjust the
detector and move the lever over the switch contacts until it is in
adjustment and then, if all your connections are properly made, you
should be able to pick up messages.
[Illustration: Wireless Set made into a Ring, designed by Alfred G.
Rinehart, of Elizabeth, New Jersey. This little Receptor is a
Practical Set; it will receive Messages, Concerts, etc., Measures 1"
by 5/8" by 7/8". An ordinary Umbrella is used as an Aerial.]
APPENDIX
USEFUL INFORMATION
ABBREVIATIONS OF UNITS
Unit Abbreviation
ampere amp.
ampere-hours amp.-hr.
centimeter cm.
centimeter-gram-second c.g.s.
cubic centimeters cm.^3
cubic inches cu. in.
cycles per second ~
degrees Centigrade °C.
degrees Fahrenheit °F.
feet ft.
foot-pounds ft.-lb.
grams g.
henries h.
inches in.
kilograms kg.
kilometers km.
kilowatts kw.
kilowatt-hours kw.-hr.
kilovolt-amperes kv.-a.
meters m.
microfarads [Greek: mu]f.
micromicrofarads [Greek: mu mu]f.
millihenries mh.
millimeters mm.
pounds lb.
seconds sec.
square centimeters cm.^2
square inches sq. in.
volts v.
watts w.
PREFIXES USED WITH METRIC SYSTEM UNITS
Prefix Abbreviation Meaning
micro [Greek: mu]. 1 millionth
milli m. 1 thousandth
centi c. 1 hundredth
deci d. 1 tenth
deka dk. 10
hekto h. 1 hundred
kilo k. 1 thousand
mega m. 1 million
SYMBOLS USED FOR VARIOUS QUANTITIES
Quantity Symbol
capacitance C
conductance g
coupling co-efficient k
current, instantaneous i
current, effective value I
decrement [Greek: delta]
dielectric constant [Greek: alpha]
electric field intensity [Greek: epsilon]
electromotive force,
instantaneous value E
electromotive force,
effective value F
energy W
force F
frequency f
frequency x 2[Greek: pi] [Greek: omega]
impedance Z
inductance, self L
inductance, mutual M
magnetic field intensity A
magnetic flux [Greek: Phi]
magnetic induction B
period of a complete
oscillation T
potential difference V
quantity of electricity Q
ratio of the
circumference of a
circle to its diameter
=3.1416 [Greek: pi]
reactance X
resistance R
time t
velocity v
velocity of light c
wave length [Greek: lambda]
wave length in meters [Greek: lambda]m
work W
permeability [Greek: mu]
Square root [Math: square root]
TABLE OF ENAMELED WIRE
No. of Turns Turns Ohms per
Wire, per per Cubic Inch
B.& S. Linear Square of
Gauge Inch Inch Winding
20 30 885 .748
22 37 1400 1.88
24 46 2160 4.61
26 58 3460 11.80
28 73 5400 29.20
30 91 8260 70.90
32 116 21,000 7547.00
34 145 13,430 2968.00
36 178 31,820 1098.00
38 232 54,080 456.00
40 294 86,500 183.00
TABLE OF FREQUENCY AND WAVE LENGTHS
W. L.--Wave Lengths in Meters.
F.--Number of Oscillations per Second.
O. or square root L. C. is called Oscillation Constant.
C.--Capacity in Microfarads.
L.--Inductance in Centimeters.
1000 Centimeters = 1 Microhenry.
W.L. F O L.C.
50 6,000,000 .839 .7039
100 3,000,000 1.68 2.82
150 2,000,000 2.52 6.35
200 1,500,000 3.36 11.29
250 1,200,000 4.19 17.55
300 1,000,000 5.05 25.30
350 857,100 5.87 34.46
400 750,000 6.71 45.03
450 666,700 7.55 57.00
500 600,000 8.39 70.39
550 545,400 9.23 85.19
600 500,000 10.07 101.41
700 428,600 11.74 137.83
800 375,000 13.42 180.10
900 333,300 15.10 228.01
1,000 300,000 16.78 281.57
1,100 272,730 18.45 340.40
1,200 250,000 20.13 405.20
1,300 230,760 21.81 475.70
1,400 214,380 23.49 551.80
1,500 200,000 25.17 633.50
1,600 187,500 26.84 720.40
1,700 176,460 28.52 813.40
1,800 166,670 30.20 912.00
1,900 157,800 31.88 1,016.40
2,000 150,000 33.55 1,125.60
2,100 142,850 35.23 1,241.20
2,200 136,360 36.91 1,362.40
2,300 130,430 38.59 1,489.30
2,400 125,000 40.27 1,621.80
2,500 120,000 41.95 1,759.70
2,600 115,380 43.62 1,902.60
2,700 111,110 45.30 2,052.00
2,800 107,140 46.89 2,207.00
2,900 103,450 48.66 2,366.30
3,000 100,000 50.33 2,533.20
4,000 75,000 67.11 4,504.00
5,000 60,000 83.89 7,038.00
6,000 50,000 100.7 10,130.00
7,000 41,800 117.3 13,630.00
8,000 37,500 134.1 18,000.00
9,000 33,300 151.0 22,820.00
10,000 30,000 167.9 28,150.00
11,000 27,300 184.8 34,150.00
12,000 25,000 201.5 40,600.00
13,000 23,100 218.3 47,600.00
14,000 21,400 235.0 55,200.00
15,000 20,000 252.0 63,500.00
16,000 18,750 269.0 72,300.00
PRONUNCIATION OF GREEK LETTERS
Many of the physical quantities use Greek letters for symbols. The
following is the Greek alphabet with the way the letters are
pronounced:
a alpha
b beta
g gamma
d delta
e epsilon
z zeta
ae eta
th theta
i iota
k kappa
l lambda
m mu
n nu
x Xi(Zi)
o omicron
p pi
r rho
s sigma
t tau
u upsilon
ph phi
ch chi
ps psi
o omega
TABLE OF SPARKING DISTANCES
In Air for Various Voltages between Needle Points
Volts Distance
Inches Centimeter
5,000 .225 .57
10,000 .470 1.19
15,000 .725 1.84
20,000 1.000 2.54
25,000 1.300 3.30
30,000 1.625 4.10
35,000 2.000 5.10
40,000 2.450 6.20
45,000 2.95 7.50
50,000 3.55 9.90
60,000 4.65 11.8
70,000 5.85 14.9
80,000 7.10 18.0
90,000 8.35 21.2
100,000 9.60 24.4
110,000 10.75 27.3
120,000 11.85 30.1
130,000 12.95 32.9
140,000 13.95 35.4
150,000 15.00 38.1
FEET PER POUND OF INSULATED MAGNET WIRE
No. of Single Double Single Double
B.& S. Cotton, Cotton, Silk, Silk, Enamel
Gauge 4-Mils 8-Mils 1-3/4-Mils 4-Mils
20 311 298 319 312 320
21 389 370 408 389 404
22 488 461 503 498 509
23 612 584 636 631 642
24 762 745 800 779 810
25 957 903 1,005 966 1,019
26 1,192 1,118 1,265 1,202 1,286
27 1,488 1,422 1,590 1,543 1,620
28 1,852 1,759 1,972 1,917 2,042
29 2,375 2,207 2,570 2,435 2,570
30 2,860 2,534 3,145 2,900 3,240
31 3,800 2,768 3,943 3,683 4,082
32 4,375 3,737 4,950 4,654 5,132
33 5,590 4,697 6,180 5,689 6,445
34 6,500 6,168 7,740 7,111 8,093
35 8,050 6,737 9,600 8,584 10,197
36 9,820 7,877 12,000 10,039 12,813
37 11,860 9,309 15,000 10,666 16,110
38 14,300 10,636 18,660 14,222 20,274
39 17,130 11,907 23,150 16,516 25,519
40 21,590 14,222 28,700 21,333 32,107
INTERNATIONAL MORSE CODE AND CONVENTIONAL SIGNALS
TO BE USED FOR ALL GENERAL PUBLIC SERVICE RADIO COMMUNICATION
1. A dash is equal to three dots.
2. The space between parts of the same letter is equal to one dot.
3. The space between two letters is equal to three dots.
4. The space between two words is equal to five dots.
[Note: period denotes Morse dot, hyphen denotes Morse dash]
A .-
B -...
C -.-.
D -..
E .
F ..-.
G --.
H ....
I ..
J .---
K -.-
L .-..
M --
N -.
O ---
P .--.
Q --.-
R .-.
S ...
T -
U ..-
V ...-
W .--
X -..-
Y -.--
Z --..
Ä (German) .-.-
Á or Å (Spanish-Scandinavian) .--.-
CH (German-Spanish) ----
É (French) ..-..
Ñ (Spanish) --.--
Ö (German) ---.
Ü (German) ..--
1 .----
2 ..---
3 ...--
4 ....-
5 .....
6 -....
7 --...
8 ---..
9 ----.
0 -----
Period .. .. ..
Semicolon -.-.-.
Comma -.-.-.
Colon ---...
Interrogation ..--..
Exclamation point --..--
Apostrophe .----.
Hyphen -....-
Bar indicating fraction -..-.
Parenthesis -.--.-
Inverted commas .-..-.
Underline ..--.-
Double dash -...-
Distress Call ...---...
Attention call to precede every transmission -.-.-
General inquiry call -.-. --.-
From (de) -.. .
Invitation to transmit (go ahead) -.-
Warning--high power --..--
Question (please repeat after ...)--interrupting long messages ..--..
Wait .-...
Break (Bk.) (double dash) -...-
Understand ...-.
Error ........
Received (O.K.) .-.
Position report (to precede all position messages) - .-.
End of each message (cross) .-.-.
Transmission finished (end of work) (conclusion of correspondence) ...-.-
INTERNATIONAL RADIOTELEGRAPHIC CONVENTION
LIST OF ABBREVIATIONS TO BE USED IN RADIO COMMUNICATION
ABBREVIATION QUESTION ANSWER OR REPLY
PRB Do you wish to communicate I wish to communicate by means
by means of the International of the International Signal Code.
Signal Code?
QRA What ship or coast station is This is....
that?
QRB What is your distance? My distance is....
QRC What is your true bearing? My true bearing is....
QRD Where are you bound for? I am bound for....
QRF Where are you bound from? I am bound from....
QRG What line do you belong to? I belong to the ... Line.
QRH What is your wave length in My wave length is ... meters.
meters?
QRJ How many words have you to send? I have ... words to send.
QRK How do you receive me? I am receiving well.
QRL Are you receiving badly? I am receiving badly. Please
Shall I send 20? send 20.
...-. ...-.
for adjustment? for adjustment.
QRM Are you being interfered with? I am being interfered with.
QRN Are the atmospherics strong? Atmospherics are very strong.
QRO Shall I increase power? Increase power.
QRP Shall I decrease power? Decrease power.
QRQ Shall I send faster? Send faster.
QRS Shall I send slower? Send slower.
QRT Shall I stop sending? Stop sending.
QRU Have you anything for me? I have nothing for you.
QRV Are you ready? I am ready. All right now.
QRW Are you busy? I am busy (or: I am busy with...).
Please do not interfere.
QRX Shall I stand by? Stand by. I will call you when
required.
QRY When will be my turn? Your turn will be No....
QRZ Are my signals weak? You signals are weak.
QSA Are my signals strong? You signals are strong.
QSB Is my tone bad? The tone is bad.
Is my spark bad? The spark is bad.
QSC Is my spacing bad? Your spacing is bad.
QSD What is your time? My time is....
QSF Is transmission to be in Transmission will be in
alternate order or in series? alternate order.
QSG Transmission will be in a
series of 5 messages.
QSH Transmission will be in a
series of 10 messages.
QSJ What rate shall I collect for...? Collect....
QSK Is the last radiogram canceled? The last radiogram is canceled.
QSL Did you get my receipt? Please acknowledge.
QSM What is your true course? My true course is...degrees.
QSN Are you in communication with land? I am not in communication with land.
QSO Are you in communication with I am in communication with...
any ship or station (through...).
(or: with...)?
QSP Shall I inform...that you are Inform...that I am calling him.
calling him?
QSQ Is...calling me? You are being called by....
QSR Will you forward the radiogram? I will forward the radiogram.
QST Have you received the general General call to all stations.
call?
QSU Please call me when you have Will call when I have finished.
finished (or: at...o'clock)?
QSV Is public correspondence being Public correspondence is being
handled? handled. Please do not interfere.
[Footnote: Public correspondence is any radio work, official or
private, handled on commercial wave lengths.]
QSW Shall I increase my spark Increase your spark frequency.
frequency?
QSX Shall I decrease my spark Decrease your spark frequency.
frequency?
QSY Shall I send on a wavelength Let us change to the wave length
of ... meters? of ... meters.
QSZ Send each word twice. I have
difficulty in receiving you.
QTA Repeat the last radiogram.
When an abbreviation is followed by a mark of interrogation, it refers
to the question indicated for that abbreviation.
Useful Information
Symbols Used For Apparatus
alternator
ammeter
aerial
arc
battery
buzzer
condenser
variable condenser
connection of wires
no connection
coupled coils
variable coupling
detector
gap, plain
gap, quenched
ground
hot wire ammeter
inductor
variable inductor
key
resistor
variable resistor
switch s.p.s.t.
" s.p.d.t.
" d.p.s.t.
" d.p.d.t.
" reversing
phone receiver
" transmitter
thermoelement
transformer
vacuum tube
voltmeter
choke coil
DEFINITIONS OF ELECTRIC AND MAGNETIC UNITS
The _ohm_ is the resistance of a thread of mercury at the temperature
of melting ice, 14.4521 grams in mass, of uniform cross-section and a
length of 106.300 centimeters.
The _ampere_ is the current which when passed through a solution of
nitrate of silver in water according to certain specifications,
deposits silver at the rate of 0.00111800 of a gram per second.
The _volt_ is the electromotive force which produces a current of 1
ampere when steadily applied to a conductor the resistance of which is
1 ohm.
The _coulomb_ is the quantity of electricity transferred by a current
of 1 ampere in 1 second.
The _ampere-hour_ is the quantity of electricity transferred by a
current of 1 ampere in 1 hour and is, therefore, equal to 3600
coulombs.
The _farad_ is the capacitance of a condenser in which a potential
difference of 1 volt causes it to have a charge of 1 coulomb of
electricity.
The _henry_ is the inductance in a circuit in which the electromotive
force induced is 1 volt when the inducing current varies at the rate
of 1 ampere per second.
The _watt_ is the power spent by a current of 1 ampere in a resistance
of 1 ohm.
The _joule_ is the energy spent in I second by a flow of 1 ampere in 1
ohm.
The _horse-power_ is used in rating steam machinery. It is equal to
746 watts.
The _kilowatt_ is 1,000 watts.
The units of capacitance actually used in wireless work are the
_microfarad_, which is the millionth part of a farad, because the
farad is too large a unit; and the _C. G. S. electrostatic unit of
capacitance_, which is often called the _centimeter of capacitance_,
which is about equal to 1.11 microfarads.
The units of inductance commonly used in radio work are the
_millihenry_, which is the thousandth part of a henry; and the
_centimeter of inductance_, which is one one-thousandth part of a
microhenry.
Note.--For further information about electric and magnetic units get
the _Bureau of Standards Circular No. 60_, called _Electric Units and
Standards_, the price of which is 15 cents; also get _Scientific Paper
No. 292_, called _International System of Electric and Magnetic
Units_, price 10 cents. These and other informative papers can be had
from the _Superintendent of Documents, Government Printing Office_,
Washington, D. C.
WIRELESS BOOKS
The Admiralty Manual of Wireless Telegraphy. 1920. Published by His
Majesty's Stationery Office, London.
Ralph E. Batcher.--Prepared Radio Measurements. 1921. Wireless Press,
Inc., New York City.
Elmer E. Bucher.--Practical Wireless Telegraphy. 1918. Wireless
Press, Inc., New York City.
Elmer E. Bucher.--Vacuum Tubes in Wireless Communication. 1919.
Wireless Press, Inc., New York City.
Elmer E. Bucher.--The Wireless Experimenter's Manual. 1920. Wireless
Press, Inc., New York City.
A. Frederick Collins.--Wireless Telegraphy, Its History, Theory, and
Practice. 1905. McGraw Pub. Co., New York City.
J. H. Dellinger.--Principles Underlying Radio Communication. 1921.
Signal Corps, U. S. Army, Washington, D. C.
H. M. Dorsett.--Wireless Telegraphy and Telephony. 1920. Wireless
Press, Ltd., London.
J. A. Fleming.--Principles of Electric Wave Telegraphy. 1919.
Longmans, Green and Co., London.
Charles B. Hayward.--How to Become a Wireless Operator. 1918.
American Technical Society, Chicago, Ill.
G. D. Robinson.--Manual of Radio Telegraphy and Telephony. 1920.
United States Naval Institute, Annapolis, Md.
Rupert Stanley.--Textbook of Wireless Telegraphy. 1919. Longmans,
Green and Co., London.
E. W. Stone.--Elements of Radio Telegraphy. 1919. D, Van Nostrand Co.,
New York City.
L. B. Turner.--Wireless Telegraphy and Telephony. 1921. Cambridge
University Press. Cambridge, England.
Send to the _Superintendent of Documents, Government Printing Office_,
Washington, D. C., for a copy of _Price List No. 64_ which lists the
Government's books and pamphlets on wireless. It will be sent to you
free of charge.
The Government publishes; (1) _A List of Commercial Government and
Special Wireless Stations_, every year, price 15 cents; (2) _A List of
Amateur Wireless Stations_, yearly, price 15 cents; (3) _A Wireless
Service Bulletin_ is published monthly, price 5 cents a copy, or 25
cents yearly; and (4) _Wireless Communication Laws of the United
States_, the _International Wireless Telegraphic Convention and
Regulations Governing Wireless Operators and the Use of Wireless on
Ships and Land Stations_, price 15 cents a copy. Orders for the above
publications should be addressed to the _Superintendent of Documents,
Government Printing Office, Washington, D. C._
Manufacturers and Dealers in Wireless Apparatus and Supplies:
Adams-Morgan Co., Upper Montclair, N. J.
American Hard Rubber Co., 11 Mercer Street, New York City.
American Radio and Research Corporation, Medford Hillside, Mass.
Brach (L. S.) Mfg. Co., 127 Sussex Ave., Newark, N. J.
Brandes (C.) Inc., 237 Lafayette St., New York City.
Bunnell (J. H.) Company, Park Place, New York City.
Burgess Battery Company, Harris Trust Co. Bldg., Chicago, Ill.