Multi-mode optical transceiver module

To permit transmit-receive operation of baseband AM or 15 kHz carrier frequency USB or NBFM, with self-contained battery supply.

transceiver - external      internal view

There's nothing very exciting about this unit. It's best feature is that it was well made mechanically (and uses plug-in assembles to make access simple). It even has tie-wrapped cable assemblies... Components that were to hand dominated the design process, hence the use of rather large 1.4 MHz crystal filters for audio processing and SSB generation.

Having spent a couple of years on the shelf (the unit, not me), the inner workings had been totally forgotten, so it seemed sensible to record the details here as the various circuits and drawings were painstakingly located again on one of the old PCs.

block diagram

All but one part of this wish-list block diagram (and unit front panel) came to fruition - at the moment, only a single fixed (15 kHz) carrier frequency  is provided. The original idea was to have a locked VFO that would increment in 1 kHz steps up to 25 kHz.

In operation, the 'bypass' mode allows the microphone and loud-speaker amplifier to be connected directly to the optical head unit, with initially, this being one the Finningley transceiver units. On these transceivers, the rx section has two outputs - 'baseband rx af' and 'unprocessed rx AF, the latter (with its flat frequency response)  being required for sub-carrier operation. On transmit, the Finningley units were designed to be flat up to 25 kHz anyway.

PCB circuit diagrams 

Not shown on the block diagram is a SMPSU that converts the 12v battery voltage down to 6v, which is used to power the loud-speaker chip (the very useful, low consumption CD1691CB )

6v psu pcb

Mic switching and agc

mic input

Warble tone generator

warble tone generator

Loud speaker amplifier and NBFM detector (with frequency conversion stage)

ls amplifier

USB generation and clipping

ssb generation

SSB and conversion oscillators/switching


FM modulator

FM modulator


                        External - on lid (ie, part of battery pack assembly)                                                 Main unit to lid interface

          main unit to lid connector                                  interface