[TenTec] transverters for other bands

[Dr. Gerald N. Johnson, P.E.]

I've tested the Tentec 1209 transverter and I found the PA stages are
good from at least 10 MHz up to about 60 MHz. The broad band
transformers are getting lossy at 70 MHz. I suspect they are good to
below 2 MHz. They would need redesign to work at 70 MHz. The same board
would seem to make a decent 2m to 222 transverter, certainly the
transistors are good up there, but I was unable to create balanced to
unbalanced transformers for the output and driver that were satisfactory
to me on the bench. Its probably significant that the 1210 uses a single
ended PA. It probably would be easiest to move the 1210 to 70 and 222
than to move the 1208 or 1209.

The failings I find in the 1209 are: 1. that it needs to be shielded,
the three piece case leaks like a bottomless bucket and so local
computer hash is a pain and its hard to measure MDS and blocking range
unless the generator is more than well shielded. 2. it needs to be hard
keyed or else the RF sense needs to be converted to a Schmitt trigger so
it stays saturated. I've found the PA bias to be a function of drive
level and that leads to distortion. 3. the diode switching of the
receiver losses a lot of potential signal, a 1 dB NF transistor delivers
only a 7 dB NF. The rest is lost to the PA which isn't solidly
disconnected from the antenna. I'll probably make both inputs and
outputs as separate lines so I have only one TR switch, at the antenna.

The 6m receiver parts can be tuned most anywhere from DC to 1296 (though
the board isn't suited for much above 450 MHz) and work well if local
oscillator injection can be supplied. I suspect that the discrete diode
ring mixer could be profitably replaced by something from MCL and would
work far better.

73, Jerry, K0CQ

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