[Elecraft] IMD and CW

[Fred Jensen]

Not CW, and this probably won't work in 4X-land, but if you want to see 
the difference a Class-C amp makes, set your P3 span to about 6 KHz, and 
tune in WWV on its various frequencies.  During the tone-on minutes, the 
2.5 and 20 MHz signals will look as you expect an AM signal with a tone 
modulating it ... two sidebands on either side of the carrier.  If you 
look very close, you can see the 100 Hz sub-carrier, and if you narrow 
things down enough, you can see the sidebands generated around it by the 
IRIG-H time code.  These two transmitters are low level modulated with 
linear amplification.

The 5, 10, and 15 MHz transmitters are plate-modulated Class-C and look 
markedly different.  The two sidebands are there, but so are their 2nd 
and 3rd harmonics [sometimes when WWV is really strong, I can make out 
the 4th harmonic].  The 100 Hz sub-carrier and the IRIG-H sidebands are 
there as you would expect, but they also surround the audio sidebands 
and harmonics.

WWV builds one baseband with all the tones, ticks, burps, codes, and 
voice and it modulates all 5 transmitters.  The difference between the 
TX is really striking and a bit disappointing.  I've always assumed WWV 
was the "gold-standard."

Fred K6DGW
Sparks NV DM09dn
Washoe County

--Northern California Contest Club
--CU in the Cal QSO Party
--7-8 Oct 2017

On 12/22/2016 10:22 PM, Vic Rosenthal wrote:
> I didn't exactly do this, but I did investigate the effects of distortion on CW signals. I disconnected my P3 from the K3 and set the IF to 7 MHz. so it would act like a standalone spectrum analyzer.
> I was interested in whether a class-C amplifier I had built would sharpen the keying enough to create noticeable clicks. The amplifier used minimal fixed bias to allow a small amount of resting plate current in transmit mode, with full class-C operating bias provided by a grid resistor.
> I noted a broadening of the base of the signal on the P3, indicating that the signal was not as clean as the K3 alone.  But listening with another receiver on either side of the S9+30 dB signal didn't reveal audible clicks. I also asked other operators to listen and there were no reports of clicks.
> I am sure that attempting to use that amplifier (a pair of 813s) on SSB would have gotten me ridden out of town on a rail!
>
> Vic 4X6GP
>