You should check that Vester article, I've been too lazy to dig out the book. I don't know which QST it was in, but it's in the ARRL SSB manual, I think 1965 and maybe 1970.
It is small, but he gets "bilateral' by keeping the signal path constant. So the receiver's mixer doubles as a balanced modulator on transmit, or at least he has them separate but feeding crystal filter in parallel, then either the product detector is used as the transmit mixer, or again that's in parallel with the product detector. A lot less switching needed, and doable because the building blocks are general purpose. It would be harder if they were narrow band. In the seventies when the National LM373 was common (a good stage of gain that could be varied, followed by a balanced mixer stage), some built the same way, since the stages were broadband.
One of those SSB Manuals has a home made version of the SBE-33, which was an early almost transistor transceiver (the driver and output were tubes). But it too is bilateral to some extent, and maybe it's just the way the diagram goes, but it seems a cleaner bilateral scheme.
You should check that Vester article, I've been too lazy to dig out the book. I don't know which QST it was in, but it's in the ARRL SSB manual, I think 1965 and maybe 1970.
ReplyDeleteIt is small, but he gets "bilateral' by keeping the signal path constant. So the receiver's mixer doubles as a balanced modulator on transmit, or at least he has them separate but feeding crystal filter in parallel, then either the product detector is used as the transmit mixer, or again that's in parallel with the product detector. A lot less switching needed, and doable because the building blocks are general purpose. It would be harder if they were narrow band. In the seventies when the National LM373 was common (a good stage of gain that could be varied, followed by a balanced mixer stage), some built the same way, since the stages were broadband.
One of those SSB Manuals has a home made version of the SBE-33, which was an early almost transistor transceiver (the driver and output were tubes). But it too is bilateral to some extent, and maybe it's just the way the diagram goes, but it seems a cleaner bilateral scheme.
Michael