[Elecraft] K3s, KPA500, FT8 and 6 meters

[Bill Frantz]

It sounds like that signal was a harmonic of your primary signal. If it was 1KHz off, it might have been the second harmonic of a 1KHz audio tone.

These harmonics are almost certain if you are overdriving the audio chain, so checking the drive is the first thing. Your drive to the radio at 4 bars with the 5th flickering is spot on. 

Since there are so many volume controls in the audio chain — wsjtx, one or more in the computer’s audio chain, the control on the radio — you get the idea. If one of them is too high and being compensated by having another one low, that could cause the harmonics. The fix is probably to try to set them all midway in their adjustment range.

The reason the local ham asked about CAT is the way wsjtx tries to suppress harmonics. It tries to set the radio’s transmit frequency (via CAT) so that the second harmonic of the audio tone it is sending will be suppressed by the output audio bandwidth filter in the transmitter.

73 Bill AE6JV


> On Mar 30, 2022, at 18:30, Bernie and Cheryl <hamdan at ix.netcom.com> wrote:
> 
> I'm not really a big FT8 operator, but if you want to work 6 meters, that's where the action is.  Recently, a local ham sent me an email indicating that I was broadcasting, in addition to my primary FT8 signal, a secondary wider bandwidth signal about 1 khz above my primary frequency.  He suggested that I check my ALC setting, and asked whether I am using WSJT CAT control to control the transmitter (I am but don't know how that would cause me to generate the extra signal).  I am using a K3s with a KPA500.
> 
> I had thought that, when using FT8, I should have the first four bars of the ALC indicator lit, with the fifth one either lit or flickering.  Am I wrong about this?