MW0CDO wrote:
>
> Hi readers.
>
> I have just written TT regarding my Omni V which is FM'ing, and received the
> following reply:
>
> Q:
> "I have also found that the radio is FM'ing on TX, the problem being worse on
> the lower bands 160/80m where it FM's approx 500Hz between min and max RF
> out. I don't have a TEN-TEC PSU, but the unit in use is substantial and can
> supply 25A continuously and is RF hardened..other radios work fine with it.
> The PSU exhibits approx 60mV change in output voltage when in tune mode and
> varying the RF out from min to max into a dummy load or real antenna.
> Any pointers on the problem?"
>
> A:
>
> The FM is probably caused by the high ripple (60 mv) from the power supply.
> The supply should have less than > 10 mv of ripple.
"Ripple" is not to be confused with "regulation", which seems to be
happening here...
REGULATION is the 60 mv droop you are seeing between no load and full
load.
RIPPLE is the 60 Hz (half-wave rectification) or 120 Hz (full-wave
rectification) artifact that you observe riding on the DC, due to poor
filtering.
I'm not too familiar with the Omni V, but you could look at one (or
several) oscillators in the Omni you suspect are moving around and look
at the DC input to those stages, noting the regulation and ripple on
their DC feed.
Also, you could put a frequency counter on the oscillator(s) to see
which one is moving. Once you have identified it, try the usual
techniques of heat or freeze spray to see if you can get it to act up...
Good luck,
73/Carter/K8VT
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