Re: [RFI] Mysterious K3 Symptoms - RFI?

[Mike Fatchett W0MU <w0mu@w0mu.com>]

Did you get the gold pins on your K3?  The early non gold pin versions 
had various odd behaviors.  I doubt pins are it only happens with 
1000w.  You seemed to have ruled out RFI with the dummy load.  Do you 
lights dim in the shack when you key up with the amp?  How about a line 
voltage drop on the mains?   I suppose it could be the control cabling 
between the amp and rig.  All the coax connectors good and tight?
W0MU

On 3/13/2024 8:57 AM, Pete Smith N4ZR wrote:
> 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@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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