[Elecraft] IMD and CW

[Alan Bloom]

For a CW signal, the nonlinearity of a typical power amplifier should 
have the effect of shortening the rise and fall times.  That does indeed 
widen the transmitted bandwidth.  But intuitively, it seems like the 
distortion would have to be really bad to shorten the rise/fall times by 
much.  You could always compensate for it by adjusting the K3 for softer 
key shaping.

Alan N1AL



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
>
>> On 22 Dec 2016, at 23:10, K9MA <k9ma at sdellington.us> wrote:
>>
>>> On 12/22/2016 11:40, Jim Brown wrote:
>>> IMD also affects CW. What we call CW is not "continuous wave," it is a continuous wave that is 100% modulated by a rectangular wave. That rectangular wave is rich in harmonics, and excites IMD. We hear it as clicks.
>> It would be interesting to see how much IMD it takes to significantly increase key clicks of a "clean" keyed CW signal, like that of the K3.  I'd expect the effect to be small, compared to that on an SSB signal for the same level of IMD, but I could be wrong.  I suppose a simple test would be to have a local friend with a P3 watch the signal as I turned down the supply voltage on my K3.  Has anyone tried anything like that?
>>
>> 73,
>>
>> Scott  K9MA
>>
>>
>> --
>> Scott  K9MA
>>
>> k9ma at sdellington.us
>>
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