[Elecraft] [K2] Transmit Audio Problems

[Fred Jensen]

Anything other than a *perfect* sine wave will have harmonics which will 
also appear in the output spectrum.  Non-linearities within the radio 
will also create extraneous products in the output.

With a P3 or other panadapter, take a look at WWV with the radio in AM 
and the span around 6 or 7 KHz.  They create a single audio baseband 
that has all the bleeps, bloops, tones, 100 Hz subcarrier, IRIG-H 
modulation and voice announcements, and modulate 5 transmitters with it.

The 2.5 and 20 MHz signals will look pretty much like we all expect: 
The carrier surrounded very close by the two sidebands from the IRIG 
subcarrier, and when the tones are on, they clearly show up, and the 
spectrum is very clean.  These two transmitters are apparently low-level 
modulated with linear amplification.

The spectrum on 5, 10, and 15 MHz is altogether different.  You will see 
the carrier of course, surrounded very close by the IRIG subcarrier. 
You will see the two expected sidebands from the tones when they're on. 
  You will also see harmonics of the tone sidebands ... depending on 
conditions and time of day, I can sometimes see the 4th harmonic.  Each 
of the tone sidebands will have the subcarrier sidebands close around 
them, as will all the harmonics.  I believe these three transmitters are 
Class C finals plate modulated or at least that's what I read.

The difference is really striking.  It's amazing what a little 
non-linearity can accomplish. :-)

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 2014 Cal QSO Party 4-5 Oct 2014
- www.cqp.org

On 6/7/2014 11:02 AM, Vic Rosenthal wrote:
> What's the source of the 700 Hz tone? Are you sure it is clean?
> If you reduce the level of the 700 Hz tone, do the spikes go down at the
> same rate as the fundamental, or faster? If the latter, you may be
> overdriving the K2.