Interesting. My K3S (10175) and K3 (3260) exhibit the exact same
behavior. My K3S had a problem with low power stability on 80 meters
that resulted in field replacement of the 100W PA module, but the 20
meter current draw didn't change. My working hypothesis is tolerance
stack-up in the 20 meter LPF, but that's just a supposition. Both radios
have been used for fairly serious contest duty, the K3 since 2009 and
the K3S since 2016, with no reliability problems.
73...
Randy, W8FN
On 9/5/2020 10:20 PM, ab2tc wrote:
Hi,
I have recently made a discovery during a routine checkup that my K3S draws
*much* more TX current on 20 m than any of the other bands. Using Data A
FSKD mode at the 100W level it draws about 22A versus 16-18 A on all other
bands. DC voltage from the Powerwerx SS-30DV is 14.2V as measured at the
binding posts. The K3S voltmeter indicates 14.2V in receive and 13.7V in
transmit mode. Current is measured with the K3S built-in ammeter (~1A in
receive). Power output is 100-102W as measured with an LP-100A on all bands
40m - 10m. TX IMD is not noticeably affected as measured using the built-in
2-tone generator. I measure maybe 33dB (5th order worst case) below PEP on
40m slowly worsening to 30dB on 10m, all within acceptable limits for a
solid state 12VDC powered transmitter.
What's up with this? I don't know how long this has been been a "problem" as
this is not something I routinely monitor. My much older K3 (with the old
bipolar PA) does *not* exhibit this behavior. Is this indicative of a
problem with the 20m low-pass filter perhaps? All measurements are done with
a Ridge Electronics dummy load. All RF connections are tight and the LP-100A
indicates 1.01 SWR on this dummy load in all cases. BTW my serial # is
10480, which is an early serial #. It was back to Elecraft twice in its
first year for fixes to the transmit signal path to improve TX IMD.
Knut - AB2TC
PS. I am not worried about the electricity bill, but whether this is
indicative of a potential future serious failure.
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