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

Tom Rauch W8JI at contesting.com
Sun Feb 25 16:45:20 EST 2001

  Would it be feasible to use the same test setup that ARRL uses for
 > composite noise, but key the transceiver at a standard rate, both with
 > and without a standard transmit/receive offset, and look for spikes?
 > 73, Pete N4ZR
 > Contesting is!

The problem is to measure bandwidth the analyzer must have a
much narrower filter than the bandwidth you are looking at. So if
you want to measure a 3 kHz wide window the analyzer needs
perhaps a few hundred Hz bandwidth. (Same thing checking a SSB
signal with a receiver, you can NOT tell how wide someone really is
if you simply listen on a 3 kHz filter. You need to use a narrow filter
to measure the other fellow's signal.) If you don't do that, the result
is  the sum of the bandwidths of both pieces of equipment.

Now if you picture what the analyzer does, it sweeps frequency at
a slow rate compared to the bandwidth. If you simply did one
sweep you'd not have any idea what the bandwidth was, because
the analyzer would only be at one spot looking when the "splatter
or click occurred.

Unfortunately that's what most laymen do, when they try to
measure bandwidth. I've yet to see a meaningful bandwidth plot yet
of an amateur rig, except for the few I have made here out of

What you need to do is steadily modulate the rig (or key it on CW)
and store the peak energy on each random sweep across the
frequency. Then you display the absolute peak values recorded at
each frequency after many hundreds of sweeps. I don't know
anyone who does that in reviews, although it is done all the time in
commercial transmitter testing. I have to do it here when applying
for FCC certification on new commercial two-way FM radios for
land mobile applications!

That would be a good thing to include in reviews, and the ARRL
almost certainly must have a way to do that. Maybe we should ask
for proper transmitter bandwidth measurements? Clicks or splatter
that is 50 dB down means more to us than composite noise that is
over 100 dB down, or the virtually useless envelope waveforms.

How many radio manufacturers would you suppose know how to
test radios, and actually test them properly for transmitter

73, Tom
(W8JI at akorn.net) 

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