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
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