ANOTHER DIRECT CONVERSION HF SSB TRANSCEIVER
|PLL VCO||DDS VFO|
|Tayloe Mixer/Detector||Exciter & Receiver Audio|
Transceiver General Description
The transceiver which is a Direct Conversion design covers the 80, 75, 40 and 20 metres bands and employs the phasing type method of generating and detecting SSB signals. The receiver is capable of continuous coverage if an LO frequency of four time the operating frequency can be provided for the quadrature signal generator for the Tayloe detector as this is broad banded and only has upper frequency limitations. The transceiver, the transmit part of which is just an exciter is made up of eight modules or circuit boards. As the project is experimental, this format allows me to make changes without having to rebuild the entire radio. I can say that I have done several circuit changes to just about every board with the VCO and PLL boards and to a lesser extent the Tayloe Mixer board receiving the most modifications.
The following block diagram describes the Receiver/Exciter.
A High Frequency VCO provides a square wave signal for the Local Oscillator that drives the transmit and receive Tayloe Mixers. The VCO is phased locked to a DDS VFO and its output frequency is processed to provide the required Local Oscillator for the three bands. The audio output of the receive detector after post amplification goes to the receive audio phase shift board that provides unwanted sideband suppression. The audio output from this board goes to the AF Amplifier board where the signal is processed by a High Pass/Low Pass Filter circuitry and then to an amplifier to drive the loud speaker.
The microphone amplifier board amplifies the microphone signal and offers some high pass and low pass filtering to maintain a 300 to 3000 Hz audio bandwidth. There is also a keyed 800 Hz oscillator on board that can be used for testing. Out of this board the signal goes to the transmit audio phase shift network which in turn drives the four channel amplifiers associated with the transmit Tayloe Modulator.
The RF ends of the mixers are tied to a common coupling that is connected to a low pass filter for the operating frequency. Though not optimum, this provides a reasonable level of receiver front end selectivity. Not included in the block diagram is a planned PA that will produce about 20 watts P.E.P. from the drive coming out of the modulator.