[Elecraft] IMD and CW

[K9MA]

Very interesting, Fred.  It makes sense, though, that plate modulated 
class-C amplifiers aren't terribly linear.  On the other hand, that kind 
of distortion probably doesn't affect WWV's mission.

I wonder if the AM broadcast industry achieves lower distortion. 
Feedback comes to mind.

73,

Scott  K9MA

  On 12/23/2016 15:53, Fred Jensen wrote:
> 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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-- 
Scott  K9MA

k9ma at sdellington.us