[Elecraft] XV432 transverter note

[chetsubaccount at snet.net]

Hello fellow owners,

I am posting this here in case it may help others solve some issues they
have.

The past weekend contest presented a good opportunity to test a recent
modification to my Elecraft XV432 transverter.

In the last contest I noticed that its frequency stability was not
sufficient for dependable FT-8 operation. As it went thru transmit cycles,
the received signals on the waterfall would slowly arc over on a curved
trajectory. It took about 15 minutes of operation to settle down

I theorized that the high FT-8 duty cycle raised its internal temperature
faster than its local oscillator crystal oven could compensate. The little
fan inside simply spread the heat from the PA around to the whole unit. 

In a separate box I rigged a freq synthesizer (from Q5, having a nice TCXO)
set to produce the required LO frequency. The LO in the transverter was
disabled with a jumper from its transistor's base to ground. A BNC connector
added to the side of the transverter near the internal LO circuit allowed
for a small capacitor to then couple in the synthesized signal, and LO
levels and alinement were similar to the original.

It worked well! Now I get quick answers to my FT-8 transmissions. And, it is
interesting to watch other's signals on the waterfall- some are obviously
stable with a vertical series of transmissions, but others have curving
trajectories, often seen when they would first start up on the band, and
those stations were often difficult or impossible to contact as their
frequency moved.

My XV144 and XV222 transverters do not seem to suffer the same problem but
will get a closer look in the future.

73,
Chet, N8RA