Amplitude Modulation on FM.

[wa9fvp]

When operating 6 meter FM I'm seeing amplitude modulation on my K3.  I have the all the upgrades including the KIO3B and the KSYN3A.  Into a 50 ohm load at 200 watts the KPA500 peaks at 300 watts. I disconnected the IO cables including USB but nothing changed.

[Don Wilhelm]

Jack,

What does the FM output look like direct from the K3?
In other words, disconnect the KPA500 and see if the AM problem is still
present.
That will tell you whether it is a K3 problem or a KPA500 problem.

Do not overlook the possibility that it is RF feedback getting into
something.  If the problem gets worse with increased power, suspect
RFI.  Also working into a dummy load should eliminate the possibility of
RFI.  If RFI is the problem, better common mode chokes on your antenna
and tighter feedline connections are the tools to attack it.

Also monitor the AC voltage during transmit as well as the output
voltage of your power supply. If one or both sag substantially, that
problem should be fixed first - for the AC side, better wiring to the AC
receptacle (dedicated circuit), and for the power supply output, either
tighter connections or larger wire, or there could be an internal
problem in the power supply.

73,
Don W3FPR

On 5/3/2016 6:17 PM, wa9fvp wrote:

> When operating 6 meter FM I'm seeing amplitude modulation on my K3.  I have
> the all the upgrades including the KIO3B and the KSYN3A.  Into a 50 ohm load
> at 200 watts the KPA500 peaks at 300 watts. I disconnected the IO cables
> including USB but nothing changed.
>
>
>
> -----
> Jack WA9FVP
>
> Sent from my TRS-80 :-)
> --
> View this message in context: http://elecraft.365791.n2.nabble.com/Amplitude-Modulation-on-FM-tp7617137.html
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[wa9fvp]

I think I know the problem.  My widest filter is 6KHz, I'll have replace it with the 13KHz filter.