SSB Radiotelephone TRA55

The TRA55 is an early SSB transceiver rated at 60 watts output and operates on four crystal -controlled channels, two in the 3 to 6 -Mc /s band and two in the 6 to 12 -Mc /s band.

For transmission, a switch in the handle of the telephone - microphone handset must be depressed. A built -in loudspeaker can be used, if required, in place of the telephone earpiece.

It is fully tropicalized and costs £495, less crystals, in the U.K.

The TRA55 employs the "filter" method of single sideband suppressed carrier generation. In this a balanced modulator (push-pull to AF, push-push to RF.) is used to generate a double -sideband suppressed carrier signal on a basic frequency of 1.4MHz. This is then passed into a crystal filter which attenuates the unwanted sideband by about 50dB.

The SSB signal so obtained is passed to a second balanced modulator where it is brought to the RF required by mixing with the output from a master crystal oscillator. All the crystals on which the transmitted frequency depends are kept at constant temperature in a small oven to ensure frequency stability. On " receive" the incoming signal is amplified at RF converted to 1.4 MHz IF and passed through the filter, then into a " product " or heterodyne detector (after suitable amplification). About 20dB of speech clipping is provided in the modulator AF amplifier and the number of controls has been reduced to a minimum so that the equipment can be used by non-technical personnel.

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