For those who are not familiar with what these different specs mean for
receiver performance, the ARRL prints an excellent article reviewing all
of these. I just scoured their web site and can't find it at the moment.
Alternatively, it's in the Handbook (pg. 26.43 in the 1999 edition).
It's a little difficult to understand how they all interact to describe
your receiver's performance, but once you understand a few of them, it
makes reading specs much more enlightening.
73, Duane AC5AA (still working on understanding all of them)
On Wed, 27 Oct 1999 13:04:36 -1000 "Jim Reid" <firstname.lastname@example.org> writes:
> > rig X= MDS at 80 meters-128, MDS at 20 meters-139,
> > Blocking DR at 80 meters 115, Blocking DR at 20 meters 125
> > IMD DR at 80 meters 94, IMD at 20 meters 90
> > rig Y= MDS at 80 meters-127, MDS at 20 meters-124,
> > Blocking DR at 80 meters 117, Blocking DR at 20 meters -
> > IMD DR at 80 meters 84, IMD DR at 20 meters 80
> Well, rig X certainly shows very high sensitivity on 20
> meters. However, the 15 dB delta better than rig Y may
> be comparing an apple to an orange. You must know
> what bandwidth of IF was being used! The -139 dB
> number must have been using at least a 500 Hz CW
> filter, maybe even a 250 Hz bandwidth, and a test
> of CW or steady tone minimum signal. The
> MDS signal level method should also be explained:
> was this a signal+noise oscilloscope measurement,
> just able, maybe to see a slight blip above the noise,
> or, sometimes a hole in the bottom of the noise just
> above the base band line of the scope? Or was the
> bottom of the signal brought up to be tangential with
> the average top level of the noise spectrum? This is
> usually described as a 3 dB signal to noise ratio.
> Important to know that both rigs were tested
> exactly the same way.
> More to specs than just the numbers, hi.
> Rig Y just might have been using a much
> wider IF bandwidth for the noise level to have been
> 15 dB higher, in my opinion anyway, hi.
> Does your source list the effective IF bandwidths used
> to measure these numbers? It is very important to know
> in order to do a valid comparison.
> Just my thoughts, and may not be quite correct
> in detail, hi.
> 73, Jim, KH7M
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Duane A. Calvin, AC5AA
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