[Elecraft] [K3] K3 spurious

[Julian, G4ILO]

Don Wilhelm-4 wrote:
> 
> I wonder why  this has not been seen before - surely many have used the 
> internal speaker over the past 3 years, but then again, perhaps not 
> often, I use external speakers, and many use headphones.
> 

I don't know why, Don. Perhaps it's because you really need a K3 to clearly
hear a signal 60dB down at 600Hz separation. :) But I was able to reproduce
the effect and hear it on my FT-817.

Set two receivers to CW on the same frequency. Select the narrowest filter
on the receiver. Attach the K3 to a leaky dummy load and set the power level
such that it produces a strong signal in the receiver without overloading
it. Use headphones with good acoustic isolation on the receiver. Tune the
receiver so the signal is zero-beated. Then increase the sidetone monitor
level. It may be hard to hear, because on my K3 at any rate I needed to
increase the monitor to an uncomfortably high level before I could clearly
hear the keying through the headphones, and the monitor tended to drown out
the spurious signal I was listening for. But by varying the monitor level it
was clear that I was hearing a spurious signal separated from the main one
by the amount of the sidetone frequency.

I couldn't produce a Spectran plot to illustrate the spurious next to the
main signal because distortion harmonics of the main signal (presumably
caused by the FT-817 audio stages) masked the weak spurious signal. Someone
with a panadapter might be able to see it.

Since I never use more than 100W into fairly poor antennas and normally set
the sidetone at a quiet level (4 or thereabouts) I can't see this being a
issue for me personally. If a mod is produced to fix this I think it is one
more mod that I won't bother doing. But someone who uses high power into a
beam and has the monitor turned up loud might well have a problem unless
they use headphones or external speakers.

-----
Julian, G4ILO. K2 #392  K3 #222.
* G4ILO's Shack - http://www.g4ilo.com
* KComm - http://www.g4ilo.com/kcomm.html
* KTune - http://www.g4ilo.com/ktune.html

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