> 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
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
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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