[Elecraft] Subject: Re: IMD and CW

[Bill Mader]

Falling supply voltage has a significant effect up the K3's SSB signal!
During a past FD, the CW Team Captain stopped the SSB station to ask what we
had changed.  He was then receiving a lot of "splatter" on 20 CW while we
operated on 20 SSB.

It turned out someone had accidentally knocked the surge
suppressor/multi-outlet switch to the off position.  The K3 automatically
switched to the backup battery and the logging laptop kept on playing with
nobody the wiser.  Eventually, the battery dropped to a "low" level (greater
than the 11 Volt threshold), the CW station could hear the SSB splatter!

Returning the switch to the ON position solved the problem and the battery
recharged, ready for any further incidents.  None occurred.  Since this same
problem didn't occur at the CW or GOTA stations, we didn't experience the
same issue at the SSB station.  At various times, we had all three stations
on 20m, 15m, or 40m at once!  That is why we only operated Elecraft rigs.

BTW, we took 4th overall that year!

73, Bill, K8TE
Activities Manager, Albuquerque DX Association

Message: 3
Date: Fri, 23 Dec 2016 10:11:58 -0800
From: Alan Bloom <n1al at sonic.net>
To: elecraft at mailman.qth.net
Subject: Re: [Elecraft] IMD and CW
Message-ID: <d62e9b4d-8a95-6119-b7a4-af79d40bc347 at sonic.net>
Content-Type: text/plain; charset=windows-1252; format=flowed

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