The Codan 6801 is an older SSB transceiver using a single crystal per simplex SSB channel, for up to 10 channels. The channel switch selects the crystal and also a band pass filter for that channel.
The cost of crystals to populate the 6801 runs towards $1000. A recent project implemented a functional replacement for the crystals using PllLdr and an inexpensive DDS module.The cost of crystals to populate the 6801 runs towards $1000. A recent project implemented a functional replacement for the crystals using PllLdr and an inexpensive DDS module suitable for use in the ham bands.
Above, the modified radio with 8 channels on ham bands (this radio is missing the last two channel filters, so it is only equipped internally for 8 channels).
Above is a block diagram of the DDS crystal replacement. This is not a VFO, it remains a channelised radio. The radio design does not lend itself to a VFO for several reasons, the strongest being the narrow bandwidth of the channel filters.
The full project description is at PllLdr application – ATTiny44 & AD9833 in Codan 6801.