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[CQ-Contest] re:Clicks-REAL numbers.

Subject: [CQ-Contest] re:Clicks-REAL numbers.
From: W8JI@contesting.com (Tom Rauch)
Date: Sun Mar 11 09:49:35 2001
Hi All,

 > Radio        dB down at +/- 1kHz
 > Omni VI+           -50
 > 1000MP            -46
 > IC765                -44
 > Test                   -51
 > The Test was done with an HP8640B signal generator keyed on and off at
 > 40 WPM with a rise and fall time of 5 mS.

I certainly believe George when he says this is what his HP141T (
i'm not sure what plug-in he has) measured, but I don't believe the
data is actually good because:

1.) The radios I have measured have widely varying click levels at 1
kHz spacing.

2.) The radios I have measured are generally asymmetrical in click-
distribution above and below the operating frequency.

3.) The test signal results.
        a.) bandwidth required for rise and fall time of a pulse is given
by close approximation as BW=.35 over time in seconds. So the 5
mS test signal should require (since it is DSB modulation) 140 Hz
n bandwidth (+70 -70 Hz).

        b.) page 12.2 of the 1995 ARRL Handbook has a graph based
on FCC system bandwidths needed for various CW baud rates. A
rise and fall of  5mS requires about 140 Hz of system bandwidth
according to CCIR and FCC data.

4.) The test generator is just as wide as a Ten-Tec radio with much
faster rise and fall times.

5.) The Ten Tec is barely better than some clicky radios, and when
W8LRL switched yesterday from a 1000MP to a Ten Tec Omni his
clicks totally vanished. (This is a sample of one radio, I know...)

5.) I got out a HP141T and used a 8553B RF section (which seems
to best fit the job) and my IC-751A's measured -50 dB at + - 1kHz.
So did my HP signal generator, when modulated with a 5 mS rise
and fall! So did a Ten Tec Corsair II, and my FT1000D !  Everything
is about 2 kHz BW at about 50 dB down on my HP-141T and
8553B plug in.

Even a pure unmodulated carrier, absolutely stable, showed well
over 1 kHz of bandwidth at -50 dB when I used the 100Hz
bandwidth setting of my 141T analyzer and the best plug-in I
had...a 8553B!!!!

6.) When I measured the same equipment on a Sierra Selective
level meter, there was a big difference in occupied bandwidth! A 5
mS rise and fall on my signal generator went from about 2 kHz BW
down to about 300 Hz BW at -50dB when I switched measurement

7.) When I listened on a receiver, it agreed with the Sierra  level
meter and disagreed with my HP-141T / 8553B.

Respectfully, I think the 141T and whatever plug-in we might have
can not be used to measure what we are trying to measure. We
are better off to use our receivers than something like a 141T.

I certainly trust George's integrity, but I don't trust his HP-141T at
all in this application. It is a poor instrument for the job.

73, Tom W8JI

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