[Elecraft] RF feedback?

[K2QI]

Thank you Monty, I'll try to isolate the source through elimination as
you've suggested.  I'll have to source some ferrite cores for the power
cables. I do have an airwound choke at the antenna's feedpoint, but that
will be replaced shortly with a toroidal choke.  Unfortunately, none of the
station components are grounded at the moment.  That's something else I'm
working on.

I am curious though; your previous email mentioned rectification of audio in
the wattmeter, feedline or antenna.  Could you expound on that a little
bit?  I'm wondering how it's possible for this phenomenon to worsen as the
microphone gain is reduced?  At a mic drive level of 15 on the K3 and using
the Elecraft hand mic, it rarely trips the SWR alarm.  However, if turned
down to 2 or 4, it trips the alarm more often.  When turning the mic gain
down to 0, there is no problem.

Also, keying the amplifier when using FSK-D for a continuous carrier shows
no RF spike or anomaly.  In fact, I can key the amp using just about every
mode the K3 has and it's fine. This issue only manifests itself randomly
when operating sideband.  I can key down on FSK-D and get 1100w carrier with
no interference or issue whatsoever.  Even my PC which is directly
underneath the amplifier and does not have any RF suppression works without
problem.

Oddly enough however, I cannot recreate the issue when operating sideband
into a dummy load.

This brings me back to your question about audio rectification; what is it
and how can I isolate/eliminate it?  It does not seem at this point to be an
RF issue, or at least RF from the antenna getting into the meter as 1100w
constant carrier does not trip the alarm.

Thanks and 73,
James K2QI




On Tue, Jul 14, 2009 at 9:47 AM, Monty Shultes <montys at mindspring.com>wrote:

> James,
> With all that gear in the RF chain, I would eliminate them one at a time to
> see if the problem goes away.  I would also treat all power leads - esp
> SB610 and the SWR meter if it has power - with ferrite beads.  I have
> ferrite on the K3 power cable and a common mode choke on the antenna
> coax.for my 80-40 antenna (80 meter half-wave fed with open wire line thru a
> balun).
>
> Good hunting - Monty
>
> The "cheap SWR meter" can be replaced by the K3's SWR meter - that's how I
> check my amp and antenna tuning.
>
> The wattmeter is between the antenna and SB-220.  Actually the way I have
>> everything setup is as follows: K3 > cheap SWR meter > SB-220 > SB-610>
>> watt
>> meter > antenna.
>>
>> I forgot to mention as well last night that I cannot recreate the problem
>> when keying down into a dummy load.  Only when the K3 is in sideband mode
>> and using the antenna do I get an RF surge.  It's driving me batty, so any
>> assistance is greatly appreciated.
>>
>> James K2QI
>>
>>
>> -----Original Message-----
>> From: Monty Shultes [mailto:montys at mindspring.com]
>> Sent: Tuesday, July 14, 2009 7:11 AM
>> To: K2QI
>> Subject: Re: [Elecraft] RF feedback?
>>
>> James,
>>
>> Is the wattmeter between the SB220 and antenna or between the rig and
>> SB220?
>>
>> If the former, sounds like a rectification of audio in the wattmeter,
>> feedline or antenna.  If the later, suspect the wattmeter.
>>
>> If not done, bond all units together.  This solved other problems for me
>> and
>>
>> maight work for you.
>>
>> Monty  K2DLJ
>>
>> I've noticed that I get some sort of RF feedback spike when using the
>>> SB-220
>>> and keying up in sideband mode.  It's enough to trip my SWR alarm in my
>>> wattmeter.  What is odd is that it doesn't happen on keydown CW.  The
>>> problem also gets worse when keying up in sideband mode with mic gain
>>> turned
>>> down lower.  If I raise mic gaini, the RF feedback isn't as bad and the
>>> alarm doesn't trip as often.  Thoughts?
>>>
>>> James K2QI
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>>
>