Building a 100 Mile C.W. Telegraph Set

The Radio Amateur's Hand Book, by A. Frederick Collins is part of HackerNoon’s Book Blog Post series. You can jump to any chapter in this book here: [LINK TO TABLE OF LINK]. Chapter XVII - Continuous Wave Telegraph Transmitting Sets with Alternating Current

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. Now, 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.

Photograph unavailable--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.

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.

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.

Photograph unavailable--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.

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Collins, A. Frederick. 2002. The Radio Amateur's Hand Book. Urbana, Illinois: Project Gutenberg. Retrieved April 2022, from https://www.gutenberg.org/files/6934/6934-h/6934-h.htm#chap17

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