[Elecraft] Keying Bandwidth Mod

[al_lorona@agilent.com]

Hi, Everybody,

I installed the keying bandwidth mod last night and all looks very good.
Using K6SE's suggestion of tuning across the K2 signal (sending a string
of dits) with a 50 Hz filter on another receiver, the clicks fall off
into the noise at about +- 300 Hz, but this is a really rough and
conservative estimate. I would think that Spectrogram would give me a
better view of the signal bandwidth, but I haven't tried that yet.

(When performing this measurement, you need to distinguish between
actual clicks and phase noise in the receiver. Further out beyond +- 300
Hz you can still hear something, but that is reciprocal mixing due to
the phase noise in the receiver's local oscillator. There is a very
definite difference listening to the K2 with a Kenwood and a Ten Tec in
this regard.)

The difference is also audible. Subjectively and qualitatively speaking,
as I listen to the new signal with an SSB-width filter I realize that
the keying has cleaned up and doesn't have as hard an edge to it any
more. You may want to make recordings of your K2 before and after the
mod so you can hear for yourself.

It is surprising what just one more pole of RC filtering can do for the
transmitted bandwidth, and it convicts all manufacturers of ham radios
of lazy engineering for lack of a single resistor and capacitor. Once
again, the elegant Elecraft solution out-designs the Big Three (Four?).

George W5YR's comments are really interesting. I had not thought that
this type of mod will actually increase the power density by confining
the signal power to a narrower bandwidth, but it's true. It's not too
large an increase, however, since by the time the click sidebands are
down by -20 dB that's only 1/100 the power at the peak. In FM, those
would be considered "insignificant sidebands", so the power gain isn't
anything more than academic except in the most egregious cases of
clicks. The real gain is in the reduction of splatter onto your
neighbors, and for this alone the mod should be done. If you have the
time, energy, and money, please do it.=20

There was another reason for my performing the mod, because in my case I
intend to inform others of their excessively wide signals as the
opportunity presents itself, and so I want my own signal to be clean,
lest I criticize my fellow ham while my own signal is just as bad or
worse.

Do it!

Regards,

Al  W6LX