The Radio Amateur's Hand Book Part 13

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.

[Ill.u.s.tration: 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 princ.i.p.al 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-pa.s.s 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.

[Ill.u.s.tration: Fig. 81.--Alternation Current Power Transformer. (For C. W. Telegraphy and Wireless Telephony.)]

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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.

[Ill.u.s.tration: 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.

[Ill.u.s.tration: Broadcasting Government Reports by Wireless from Was.h.i.+ngton. 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 pa.s.sed 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 s.p.a.ce 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_.