A SINGLE-SIDEBAND SHORT-WAVE SYSTEM 



495 



single-sideband transmissions in which the carrier is either totally or 

 partially suppressed such a simple receiver is not adequate, as the 

 distortion produced in a simple rectifier would be excessive. It is 

 necessary that a carrier of the right frequency and of an amplitude 

 considerably greater than that of the sidebands be present in the 

 rectifier. After a study of the situation it was decided to build up the 

 carrier for monitoring purposes from the same crystal oscillators used 

 in the transmitter. The monitoring device, a schematic of which is 

 shown in Fig. 3, consists of two detectors and a harmonic generator 



HIGH FREQUENCY 

 CRYSTAL OSCILLATOR 

 INPUT ^ 



AUDIO 

 OUTPUT 



2625 KC 

 INPUT 



Fig. 3 — Schematic of transmitting monitoring device. 



which take the high-frequency carrier and combine it with the signal 

 to produce an intermediate frequency, which is in turn beaten with 

 the 2,625 kc. derived from the low-frequency carrier crystal to obtain 

 a demodulated voice frequency. 



Receiver 

 The front view of the receiver is shown in Fig. 4. The receiver is 

 mounted in a steel cabinet seven feet high and a standard telephone 

 bay in width. Figure 5 shows a block schematic of the receiver. The 

 receiver is of the usual double-detection variety, having a high-fre- 

 quency amplifier stage, a balanced first detector, a three-stage inter- 

 mediate frequency amplifier and a balanced second detector. A 

 branch circuit, taken from the grid of the third intermediate frequency 

 amplifier tube, contains a narrow crystal filter which passes the 

 carrier, but not the sideband. After passing through the filter the 

 carrier is amplified and rectified by a linear rectifier, the rectified 

 output giving automatic volume control action on the high-frequency 

 tube, first detector, and first and second intermediate frequency 

 amplifiers. Another branch circuit passes the filtered carrier through 

 an overloaded amplifier which reduces the fluctuations of carrier 



