[Elecraft] KX3 buzz if power up on transverter band

[Drew Arnett]

Oscilloscope "screenshot" of the offending waveform:

https://drive.google.com/drive/folders/1-g9Met098lhncAcMtAAOvxWFDjf0NU_w?usp=sharing

Can anyone try to reproduce this to rule out or confirm my suspicion
it might be caused by firmware bug?

You can imagine how fast I knocked my headphones off!  :-O  :-)

Thanks and best regards,

Drew
n7da

On Wed, Aug 19, 2020 at 2:49 PM Drew Arnett <arnett.drew at gmail.com> wrote:
>
> 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