[Elecraft] Measurements on K3 TX audio

[Stewart Baker]

I had a little time to spare today so looked at my K3 TX audio.

Setup:-
K3 LSB 80m. 
Power 10W into dummy load.
Heil Pro Plus selected to the HC5 element.
Front Panel mic input High.
Tektronix 475 Oscilloscope with X10 probe connected to dummy load.

I found it necessary to set CMP to at least 5 to enable the MIC 
control to have a moderate effect. Initially MIC control set to 20 
giving the normal unprocessed RF signal display of the scope.

Increasing the CMP control to 30 made some difference to the 
display indicating that compression was taking place, but not a 
lot. The monitored audio sounded slightly louder.

Leaving CMP = 30, I increased the MIC from 20 to 60. The average 
signal of the waveform increased in line with the increase of MIC 
level, but beyond MIC =55 the background noise/ distortion became 
rather noticeable. The monitored audio sounded much louder.

I set CMP = 5 and MIC = 20 and used an external Datong RF clipper 
set to the same peak signal level into the Front Panel mic input. 
The monitored audio was at least twice as loud as the best I could 
get from the internal DSP.

Notes.
Without the external clipper I found that a lift of +2dB @ 2.4kHz 
and +4dB @ 3.2kHz improved readability.
With the external clipper the opposite was needed -2dB @ 2.4kHz 
and -4dB @3.2kHz.
Using the panel metering to set up levels was a waste of time.
The internal monitoring facility has artifacts which make accurate 
signal monitoring difficult.

Conclusion.
Out of the box the K3 produces transmit audio which sounds 
fantastic. I believe, however that for DX and contest working more 
work needs to be done on the TX audio DSP front.

Y.M.M.V

73
Stewart G3RXQ