[Elecraft] K3 low temperature VFO tuning oddity - clicking relay

[Pete Smith N4ZR]

I'll be interested to hear what you learn, Mike.  I don't have an ATU in 
my K-3, but I feed a KPA-1500, and when I QSY quickly (for example when 
pouncing on spots), I hear relays click in the amp's ATU.  I assume this 
is a function of QSYing from one ATU zone to another, every 10 or 20 KHZ 
(except on 10M, where it's 100).  It does this whether I'm transmitting 
or not.

I wonder if the firmware update you installed added this behavior to 
your K-3. I can see where it might be a good thing to adjust the ATU 
before you transmit, even if just a few milliseconds before.

73, Pete N4ZR

On 11/12/2023 2:59 PM, Michael Carter via Elecraft wrote:
> I've been getting reacquainted with my K3 (S/N 67XX)
> since adding the 100 watt PA module (KPA3A) last
> weekend.  I also updated the firmware to the latest
> versions and ran the TX Gain Calibration successfully
> at all three power levels.  The K3/10 had been sitting
> disconnected from everything since maybe 2019 when
> I used it to test the XV432 transverter I built.
>
> In operating in the early mornings this past week
> I observed an odd clicking of a relay as I tuned
> VFO A.  Additional experimentation revealed that
> VFO B would also produce the sporadic relay
> clicking while tuning that control. There was no
> apparent pattern to the clicking, i.e. no regular
> frequency interval at which clicks occurred.
>
> In both instances the relay clicking disappeared after
> a brief warm-up period.  I confirmed this behavior
> again by leaving the shack heat off and the rig off
> for a couple hours.  The Front Panel temperature and
> PA Temperature both registered 12C on a cold start
> (yes, it is New Hampshire on a fall day), and the
> anomalous relay clicking on tuning either VFO A
> or VFO B ceased once the Front Panel temperature
> rose above 17C.  This behavior was never observed
> in many years of operating the K3/10 in contests
> and general DXing, and the shack was plenty cold
> through those fall and winter mornings until the
> heat kicked up.
>
> I'll open the top cover and determine which relay
> is being activated during the cold start-up.  Both VFO
> encoders go directly to the Front Panel MCU
> with no intervening circuitry save for connectors
> and printed wiring.
>
> At first I thought the relay clicking might be from
> the internal KAT3 ATU, but this behavior occurs in
> RX mode with no effort to transmit or activate
> ATU TUNE.  It occurs with the ATU bypassed as
> well as in-circuit.  I'm now wondering if the
> MCU developed a low temperature sensitivity
> during its long hiatus from daily use?
>
> Has anyone seen this kind of low temperature
> relay clicking when tuning the receiver right after
> a cold start?
>
> Thanks in advance, and 73,
> Mike, K8CN
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