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Inside The Drake TR-7 Transceiver

by: Ronald Baker / WB4HFN

Contents   Page 1   Page 2   Page 3   >Page 4<   Page 5   Page 6   Page 7   Page 8

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The Up-Converter Board

The Up-Converter Board serves a dual function.    In the receive mode the incoming signal from the antenna passes through High Pass Filter Board to the input of the Up-Converter board.    The Up-Converter board samples the locked frequency from the Translator Board, mixes that with the incoming signal to produce the 1st IF frequency with an output at 48.05Mhz.  In the transmit mode the input to this board is the 48.05Mhz transmit IF frequency.   This IF signal is mixed with the same locked frequency from the Translator Board, to produce an output signal on the operating transmit frequency.     The transmit output of this board travels back through the High-pass Filter Board and the pin-diode switch to the transmit pre-driver stage.

The VCO Board

The VCO Board (Voltage Controlled Oscillator) function is to generate the final mixing frequency, (Injection Frequency), which is sent to the Up-Converter Board to produce the actual receive and transmit operating frequencies.    This board has two voltage controlled oscillators, one for the lower band range of 0 to 15Mhz, and a 2nd for the higher band range of 15 to 30Mhz.   Other than the actual operating frequency range both oscillators operate in the same manner and are selected according to the operating band selected.     This board also contains the phase detector and loop filter portion of the synthesizer used to produce a "locked" frequency condition when the VCO is tuned to the correct injection frequency.  

The Translator Board

The Translator Board combines signal inputs from three sources which produces a output signal between 3 and 32.5Mhz, exact frequency depending on the set tuning range of the transceiver.   This output signal is then sent to a programmable divider network which produces a 500Khz signal used to phase lock the VCO master oscillator.    

The first two signal inputs, the PTO signal, 5.05 to 5.55Mhz, and the 40Mhz reference from the Pass-Band Tuning Board, are mixed together to produce a signal between 45.05 to 45.55Mhz.   This signal is filtered and applied to a 2nd mixer stage where its mixed with the master VCO signal between 48.05 to 78.05Mhz.   The output of the 2nd mixing stage, a signal between 3 to 32.5Mhz, is applied to a programmable divider network.     The programmable divider is programmed by the Digital Board to divide the input frequency between 6 to 65, depending on the 500Khz selected tuning range of the transceiver.    The output of the programmable divider is a constant 500Khz signal when the synthesizer is phased locked to the VCO tuning frequency.

The PTO Assembly

The PTO ( Permeability-Tuned Oscillator) provides a 5.05Mhz to 5.55Mhz injection signal to the frequency synthesizer circuit.    The VCO Board tracks the frequency of the PTO to provide an overall 500Khz tuning range for the radio.  The PTO is calibrated and temperature compensating to provide a highly stable signal with a minimal drift.    The PTO includes a set of tuning dials calibrated to the PTO to provide a very accurate frequency display at the front panel.

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