[CQ-Contest] Click, click, click...

Tom Rauch W8JI at contesting.com
Sat Feb 24 20:28:47 EST 2001

Hi Clive,

I hate to bring bad news, but.....

 > Unless you have a malfunction, your MP is clean, check the Radcom and
 > QST reviews. Either way you cannot, unfortunately, alter the keying
 > characteristics of the MP( et al) the way you used to be able to do.
 > This would be a much better function than some of the silly bells and
 > whistles that come as standard.

I have no idea what RADCOM measures, but QST reviews do not
measure CW bandwidth.... nor do they measure SSB bandwidth
with valid modulation envelopes. Proper waveshape does not
guarantee proper bandwidth these days, since oscillators are
switched or moved to new frequencies at every dot and dash and
since synthesizers are being used.

As for SSB, the only proper way to measure bandwidth is with a
test signal that has multiple tones and varies at a slow (syllabic)
rates. Two-tone tests are flawed enough (they do not test power
supply or bias dynamic faults), but making matters worse the
ARRL uses dB below PEP rather than the commercial standard of
dB below one tone of two equal tones. This inflates "purity" 6dB.

Does RADCOM use dB PEP, or dB below one tone?

An Eimac tube with -42 dB 3rd order IMD, it would be -48 in an
ARRL test. Most amplifiers are far cleaner than most radios (the
exception might be tetrode PA's), when properly tuned. So the IMD
they contribute is very minor when properly tuned.

I can measure an old KWM-2 and it is -55 dB 3rd order using
commercial standards (-61dB ARRL standards). Compare that -
61dB to modern rigs at -35 to -40, and it shows things have moved

 > There is little doubt that the problem is one of overdriven amplifiers
 > not transceivers ( horrible overgeneralisation I realise)

I think the problem is rooted in many things. One is radio-to-radio
variations, like the FT-1000MP alignment problems N7DD and
others went through.

(One N4 who has a wide buzzy hissy CW signal also has a wide
cracking signal on SSB, I'm pretty sure that is the alignment of his
1000MP more than his PA.)

As these radios age, giving honest reports so people know when to
"tune-up" the radio will become more and more important.
73, Tom
(W8JI at akorn.net) 

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