[RFI] Mysterious K3 Symptoms - RFI?

[Pete Smith N4ZR]

Interesting suggestion, Mike - I use a recently-bought Samlex metered 
supply, and its analog voltmeter does not move visibly when 
transmitting.  Also checked the KPA-1500 supply, and maximum voltage 
change is -0.5 volts, from 53.1 to 52.6 from 0-1100 watts.  I realize 
that these measurements may not indicate anything about voltage swings 
occurring at a 120-Hz rate, but don't know  how I could go about checking.

73, Pete N4ZR

On 3/13/2024 10:40 AM, Michael Carter wrote:
> Hi Pete,
>
> I've not operated an amplifier at the home QTH,
> but have had similar experience with my K3
> even at 5 watts TX power.  The temporary reduction in
> receive gain, resettable by tweaking the
> AF gain control,  and the intermittent HI CURR
> warning in RX mode was ultimately traced to a failing
> electrolytic filter capacitor - in my Astron linearly
> regulated power supply!  When I tested that
> large electrolytic, its ESR was off the charts.
> The nominally regulated 13.8 VDC was dropping
> at 120 Hz rate because of the capacitor's high ESR and
> causing greatly increased current demand to
> compensate for it.  The voltage regulator didn't have
> the bandwidth to counteract the high ripple amplitude
> and frequency on its input.
>
> Changed supplies and the problem ceased to exist.
>
> I am wondering if your K3 power supply is sensitive
> to AC line voltage variations possibly caused by
> the KPA1500 even though the KPA1500 must be
> running from a separate 240 VAC circuit?
>
> 73,
> Mike, K8CN
> ------------------------------------------------------------------------
> *From:* RFI <rfi-bounces+mike.carter=unh.edu at contesting.com> on behalf 
> of Pete Smith N4ZR <pete.n4zr at gmail.com>
> *Sent:* Wednesday, March 13, 2024 10:20 AM
> *To:* Elecraft List <elecraft at mailman.qth.net>; RFI List 
> <rfi at contesting.com>
> *Subject:* [RFI] Mysterious K3 Symptoms - RFI?
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>
> Operating in this morning's CWT, and saw a recurrence of strange
> RFI-like symptoms.  After transmitting, RX gain sometimes was severely
> reduced, but simply moving the K-3's AF gain a little would cause
> recovery to normal.  Sometimes, this was accompanied by a HI CURR
> warning on the K3's display, often occurring several seconds after
> switching back to receive.
>
> My working theory has been RFI, but my station is pretty thoroughly
> fitted with toroids. Still, there seems to be a correlation between
> running my KPA-1500 at about 1100 watts and this set of symptoms, which
> I have not been able to trigger running 100 watts   To further confuse
> things, I just had another episode of this occurring *several minutes*
> after the last transmission.
>
> One culprit I can think of is a 100-foot Ethernet cable between my
> station and my FIOS router.  I have bought a shielded replacement but
> have not yet installed it.  After reading some of the recent commentary
> about so-called "shielded" cables, I'm wondering if this is worth doing.
>
> Any suggestions, either K-3-specific or more general, would be much
> appreciated.
>
> --
> 73, Pete N4ZR
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