[Elecraft] K3S line out and sidetones

[Wes]

For completeness I thought I would copy my original message for the doubters.

"I received an email from a German ham telling me that he's observing the same 
thing that I reported a couple of years ago. Specifically an audible "clicking" 
sound in both my K3S and KPA500 that coincides with CW keying.  See this thread: 
http://elecraft.365791.n2.nabble.com/KPA500-clicking-td7596512.html

Since there was no "fix" from Elecraft I guess time dulled my sensitivity to it 
until I received the email and then I thought to listen for it again.  It's 
thunderstorm season here in the AZ desert so my antenna cables are all 
disconnected. Because the problem manifests whether or not RF is being generated 
I put the K3S into TX Test mode and put the KPA500 into operate.  As before, the 
clicking is still there in both the K3S and KPA500.

But while doing this I noted that the SWR LEDs on the KAT500 were flashing.  
Since the antennas are disconnected this would be normal if RF was being 
generated, however as stated, I'm in Test mode.  One of my tuner ports has a 
dummy load attached so I switched to it and lo and behold the amp output LED was 
showing ~50W.

I have an original K3 so I tuned it to the K3S frequency, keyed the K3S and 
listened on the K3.  I could hear a non-coherent, clicky "garbage" signal that 
seemed to have a spectrum roughly the width of the TX filter.  Because both 
radios were running on the same power supply to eliminate the possibility of 
crosstalk via that path I fired up an SDR-IQ running on a totally separate 
computer and looked at the spectrum.  Although it's non-synchronous to the 
keying I can see a signal that does have an envelope roughly shaped like a BPF 
although it's far from flat in the passband.

The amplitude of this is affected by the output power setting and is present 
with the KPA500 in Standby.  It also seems to be thermally sensitive; becoming 
less conspicuous the longer things run."

Wayne replied:

Hi Wes,

TX TEST mode activates the entire TX strip because it turns on PTT to test the keying of downstream devices. This was requested by our original field testers. The only thing that isn’t turned on is the carrier. It could be that in SSB modes there’s noise in the voice passband, producing the result you observed.

I can clarify this in an errata item for the owner’s manual.

It may also be possible for me to disable the TX AF path via a DSP command, and I’ve added that to the firmware task list.

Thanks for the input--

Wayne