[Elecraft] KX3 buzz if power up on transverter band

[Drew Arnett]

Hi,

Weird problem.  Anyone else try this and do or don't see this?

Just got my KX3 back from repair.  This included an upgrade to the
latest firmware.  (Makes sense.  Requirement for production test.  I
hadn't upgraded to the very latest, because I had no need for the
latest improvements.)

Set the radio back up for 10368 to 50 MHz transverter use on XVTR1
band.  Now, if I power up the radio when it was shut down on the XVTR
band, there is a crazy loud buzz on the audio output (and
corresponding response of the S meter.)  If I switch to any other
non-XVTR band and then power up, no problem even if switching then to
the XVTR band.

FW is now 2.90/1.52I got the radio back just before the 10 GHz
contest, so only made minimal changes to settings from the cleared
state it came back in.  Changes made:
AFX mode off (was delay)
ATU bypass (can't remember if it came back this way or not.  XVTR is
good 50 ohm load.)
BAT CHG off (was not inst)
BKLIGHT off (was on)
MIC BIAS off (I think came back on; used dynamic mic during contest)
MIC BTN Ptt (was up/down)
TX DLY 10 (was 5.  abundance of caution as 5 is more than enough for
the 10 GHz rig I'm running)
XV1 on
XV1 RF 10368
XV1 IF 50
XV1 PWR 0.1
XV1 OFS (set in field) 1.20
XV1 ADR trn1
set the clock.  :-)
turned on the hidden in the menus CW-in-SSB feature

I know I turned on or off a couple of front panel things as they left
it.  Don't remember.  Stuff like vox, pre, nr or nb.  Definitely
adjusted mic gain and compression and keyer speed.  :-)

RX ISO changed to on during the contest, but problem occurs with it on or off

What does the headphone jack output look like?  Power up in bad state.
Set volume control to 20.  With no load other than 10X scope probe,
the AC component is identical for left and right.  Tip has about 0 V
DC offset.  Ring has about + 0.5 V DC offset.  AC component looks like
a the differential of a square wave.  Peak to peak amplitude is 220
mV.  (This follows volume control.  Didn't check to see if DC offset
follows volume control.)  12.2 millisecond repetition rate for
positive and negative pulses.  Negative pulse leads positive pulse by
2.2 ms, so 10 ms from positive pulse to negative.  Very small AC
ripple on that with a period of about 0.4 ms.

I was very happy to find a sequence to avoid the problem (as described
above.)  To trouble shoot, I tried to rule out a number of things.
Unplugged ALL cables from the KX3.  That did not resolve.  Tried
external 12.4 V (battery on hand) and internal battery removed.  Tried
internal battery (charged) and nothing plugged in.  No dice.

Given that it's just back from repair, that sequencing gets it in a
bad state, FW was upgraded to a new version, and audio path goes
through FW, seems reasonable to ask if this is a known FW issue or if
someone can try to reproduce this.

Hoping to figure this out before the Sept VHF, the Sept 10 GHz contest
weekend, and of course the HF contests coming up later this fall.  :-)
 With my workaround, I was able to participate in the Aug 10 GHz
weekend without interruption.  I ran a W1GHZ XVTR barefoot (+5 dBm
Pout) for best DX of 379 km.  How much fun can you have with a KX3?
Lots!  :-)

Thanks and best regards,

Drew
n7da