[hpsdr] Penny PTT unkeying spike - T/R sequencing?

[Tom Cathey]

Phil,

Another "discovery"....

I was testing an MRI  10mw in, 100w out  linear amplifier today with Penny.
Penny drove it well with a 20 db pad in-between.

However, I started getting those lockups again where Penny puts out spurious
signals and will not shut off until the power is killed. Penny has been
stable into a good dummy load with just an occasional lockup.

I added a 50 ohm resistor across Penny's RF output. This cured the problem
and is now stable with at least two amps I've tried.

I think that during unkey, there is a short time where Penny has no 50 ohm
load due to the external  PTT relay. The existing unkey spike shock I have
seems to exaggerate the condition and Penny takes off. The delay from TX to
RX probably sees Penny still on with an infinite load for an instant.   The
added constant 50 ohm resistor keeps a load on at all times.  I have more
drive than needed so this is not a problem.

That said, I'm finding Penny's output IMD to be so clean, I'm having trouble
finding a comparable pre-linear amplifier to use. I've tried MRF-150's and
might build up a class A, two-stage  tube linear with negative RF feedback.
All I need is about 30W pep to drive my KW amp system, which is already
about -40db 3rd IMD. The run of the mill -30db IMD SS amps don't seem to cut
it. Running them in full class A requires huge heat sinking and I'm thinking
it can be done easier with tubes.   

73,
Tom, K1JJ



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