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@contesting.com> on behalf of Pete
Smith N4ZR <pete.n4zr@gmail.com>
Sent: Wednesday, March 13, 2024 10:20 AM
To: Elecraft List <elecraft@mailman.qth.net>; RFI List <rfi@contesting.com>
Subject: [RFI] Mysterious K3 Symptoms - RFI?
CAUTION: This email originated from outside of the University System. Do not
click links or open attachments unless you recognize the sender and know the
content is safe.
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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