[Elecraft] RF feedback?

[K2QI]

 Hi Jim,
Thanks for the reply.  I have not noticed any power fluctuations or
increases in reflected power during the alarm event.

Antenna system is a Tarheel 100A screwdriver mounted on a tripod on my
balcony.  The balcony is about 40 feet away from the station.  The antenna
is fed with good quality Times Microwave LMR-400UF.  The last 20 feet of it
were wound into a common mode choke using 4" PVC.  The antenna does not have
a very good radial system; about 10 strands of 20g wire cut to about 12 feet
in length.  I do have a 66' length counterpoise but have not laid it yet due
to the size restrictions of the balcony (5' x 12').  The antenna's control
cable was also decoupled via a ferrite choke.

Again, 1100w constant carrier doesn't cause this problem.  Only keying up
when the K3 is in a sideband mode.  Keying up with drive power from the K3
at 100w or 50w doesn't make too much of a difference; the alarm will trip at
random times.  Dropping the drive power to about 12 watts seems to prevent
the alarm from tripping.

This phenomenon does not happen if the amp is off line.
The wattmeter is one of MFJ's new digital/analog deals.  It's the MFJ-828.

Please clarify the K3 pin 1 issue; I do not have my assembly manual in front
of me.

73 de James K2QI



>
>   On Tue, Jul 14, 2009 at 5:43 PM, Jim Brown <jim at audiosystemsgroup.com>wrote:
>
>> On Tue, 14 Jul 2009 13:44:00 -0400, K2QI wrote:
>>
>> >I am curious though; your previous email mentioned rectification of audio
>> in
>> >the wattmeter, feedline or antenna.
>>
>> As noted, one or more good common mode chokes are in order. You mentioned
>> the
>> lack of a station ground. That is a lightning safety issue, but NOT a
>> solution
>> to RFI.
>>
>> You didn't mention what your antenna system is, or how far it is from the
>> rig.
>>
>> The important question is, is this only RFI to the wattmeter, or is
>> something
>> else going on, like a spur or harmonic? Have a ham nearby listen for spurs
>> (or
>> take the antenna off another radio and listen for spurs).
>>
>> Is this an outboard wattmeter, or something built into the power amp?  If
>> outboard, my first move would be to replace the fancy wattmeter with a
>> Bird,
>> and look for fluctuations indicating increased reflected power. If you
>> don't
>> see any, I would blame the meter. If you DO still see the fluctuations, I
>> would
>> look at the K3 and the power amp. The K3 does have some pin 1 issues.
>> Ferrite
>> chokes would help with that.
>>
>> http://audiosystemsgroup.com/RFI-Ham.pdf
>>
>> 73,
>>
>> Jim Brown K9YC
>>
>>
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