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RE: 60cm Dish with Patch vs 3ft dish with offset helix feed

Hello Mike

> Anyone using the G3RUH 60cm dish with patch feed??  At what signal
> are you receiving the AO40 beacon say on average...at say MA 100 and say
> pointing angle of 20 degrees?? I am using 3 ft dish with helix feed...am
> finding out helix feed is prone to desense..problems...I think the bigger
> helix be bigger the problem...(I guess from side lobes..of 70cm

Sorry to answer a question with a question, but...

What downconverter are you using?

The reason I ask is that I've noticed with some AIDCs, if you run the d/c
off the same PSU as your TX and it is close or below the 'knee' voltage of
the internal 12V regulator, when you TX in SSB it's often difficult to hear
yourself. By running the downconverter off a separate PSU (a stack of NiCd's
in my case) I resolved the problem. I never worked out whether the problem
was desense from RF heading up the power line, the d/c's front end FET
dropping bias voltage and therefore sensitivity, or the LO changing
frequency due to the voltage dropping in TX.

73 Howard G6LVB

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