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16
RADIO AGE for October, 1926
Schnell believes that higher frequencies are more reliable than the lower frequencies for communication over the distances required by the railroad. In this connection it may be mentioned that amateur radio station 9EK at Madison, Wis., and 4 DM at Bokeelia, Fla., maintained scheduled operation on 20 meters (15,000 kilocycles) and communicated with each other twice every day from December, 1925, to May, 1926.
Use Fifty Watts
IT is believed that frequencies of 7500 kilocycles (40M) and 3750 kilocycles (80M) with power of about 50 watts to be satisfactory to provide communication between pivotal stations of the St. Paul's radio communications service. It is based on experiences of stations 9EK and 4DM and many amateurs. The transmitter is an amateur type. The accompanying drawing shows the schematic circuit diagram of the transmitter, using two 50-watt tubes, one on each half of the cycle supplied with 60 cycle current.
In making up the spiral inductances, oak or some other hardwood strips about one-half inch square will be used in supporting a brass or copper ribbon.
The radio frequency chokes 1 and 2 are designed for 14 wavelength operation for 40 meters, but will serve also for 80 meter operation. The radio frequency chokes 3 and 4 are for use in the grid leads of the tubes and while not absolutely necessary, they may help stabilize the input to the tubes.
In designing sets to be used by the railroad Schnell suggested an antenna consisting of six wires built up in the form of a cage of about 4 to 6 inches in diameter, using No. 12 enameled copper wire with the supporting pieces of substantial hardwood.
A piece of solid rod or tubing substantially guyed will be used to prevent swaying or swinging in the wind. Complete specifications for transmitting and receiving sets to be installed by the Chicago, Milwaukee & St. Paul Railway are as follows :
The Magazine of the Hour
Specifications
Ant. Antenna 33' long for 40 meter band. Antenna 66' long for 80 meter band.
Cpse. Counterpoise 31' long for 40 meter band. Counterpoise 62' long for 80 meter band.
L-l. Spiral inductance (antenna coupling) 6 turns 14" brass or copper ribbon about 1/32 " thick, spaced 14", inside diameter 3".
L-2. Same as antenna inductance except 10 turns for 40 meter band. Same as antenna inductance except 18 turns for 80 meter band.
L-l and L-2 mounted in oak strips ^"x1/^", slotted to take the ribbon.
A. Jewell Pattern 64 flush mounting 0-5 (R. F.) ammeter.
C-l. National type 450 variable transmitting condenser (.000450 mfd.).
C-2. National type 150 varia b 1 e transmitting condenser (.000150 mfd.).
C-3 C-4. Faradon model UC(Please turn to page 36)
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Schematic circuit of full wave self rectified 50 watt transmitters to be used.