I don't have an answer, I have no test gear that would even allow a look
(other than another radio). But I'm curious how you're measuring and
observing (not doubting) these results.
Except for the reports seen on the air to validate your observations; if
the radio change barely affects the results and the condition does not,
it's either a failure of both radios or the testing environment (i.e.
transmitting into the same antenna).
What happens with changes in power output, different (dummy) loads?
Then the eternal question; since this hasn't been noted before at your
station; what else is different or has changed? Have you tightened your
antenna connectors lately?
HNY,
Rick NK7I
On 1/1/2021 9:30 AM, g4piq--- via Elecraft wrote:
In general I've found the spurious performance of the K3 to be pretty good,
but I've noticed something today that I thought it would be worth asking
more widely if anyone else has seen and fixed.
I was calling CQ on 40m around 7014 kHz and I noted that several skimmers
also reported me weakly on c. 600 Hz either side of this frequency.
Sometimes skimmers have bad spurious responses, but seeing this on more than
one skimmer caused me to look more closely at my transmit spectrum. I
discovered that - particularly on 40m - there were specific frequency ranges
where a pair of sidebands appeared that move at 150% of the change in
carrier frequency. So on 7012 kHz they are at roughly +/- 500 Hz, at 7011
kHz they are at roughly +/- 1 kHz, at 7010 kHz they are at roughly +/- 1.5
kHz. They cross over with the carrier just below 7013 kHz.
Similar patterns recur in other parts of 40m, but they are strongest near
the bottom of the band. There are dramatic step changes in the level of the
spuria at the boundaries between synthesiser segments - So I see spurii from
7000-7004, none from 7004-7009, spurii 7009 -7015, etc. They peak in
strength when they are about +/- 500 Hz from the carrier, but drop
significantly in level as you get further from the carrier.
The level of these spurii is what was concerning - at their worst they were
less than 30dB down on the transmit signal. They grow somewhat non-linearly
with power. At 5W they are -40dBc, at 12W they are -32dBc, at 13W they are
-35dBc and at 100W they are a little less than -30dBc. I can see the same
style of spuria in some segments on 80m and 160m - but at lower levels.
I assumed this was a fault with that specific radio - and in some ways it is
- but the same spurii are present on both K3s that I have here - but on the
second radio they are no worse than -45dBc.
I've disconnected everything connected externally from the radio, tried
different power supplies, and recalibrated the synthesiser and Tx gain with
no significant change.
Both radios have the original synthesisers - not the KSYN3A.
Any leads from anyone on this one?
73,
Andy, G4PIQ
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