Path: utzoo!utgpu!news-server.csri.toronto.edu!clyde.concordia.ca!uunet!samsung!sdd.hp.com!ucsd!brian
From: brian@ucsd.Edu (Brian Kantor)
Newsgroups: sci.electronics
Subject: Re: VHF tranceiver specs
Message-ID: <16381@ucsd.Edu>
Date: 29 Jul 90 03:37:35 GMT
References: <1990Jul29.015732.21869@phri.nyu.edu>
Organization: The Avant-Garde of the Now, Ltd.
Lines: 39

The two measurements are often complementary.

20db quieting level is how much signal is required to cause the
no-signal unsquelched output of a receiver to decrease by 20db as
the limiters saturate out the noise; it's a simple quick measurement of
receiver sensitivity.  .2uV to .4uV is typical of modern medium-price
highband (150-170MHz) receivers.

SINAD (Signal, Interference, Noise, And Distortion) measurements are
made by applying a modulated signal to the receiver and increasing the
rf carrier level until there is a 12db signal-to-(noise+distortion) ratio,
which is supposed to simulate the level at which a typical human can
clearly understand the received signal.

20db quieting is a fast and simple measurement which does not take into
account things like hum, distortion of received audio, and miscellaneous
crud in the receiver.  SINAD is about 20 years newer, but some people
don't quote it, even though it's well over 20 years since it was
standardized.

An interesting comparison to make is to look at the respective figures
for two receivers.  If the ratio between the quieting and SINAD for one
receiver is different from the ratio for another, there is quite likely
going to be a notable difference between their performance in weak
signal conditions.  I'd choose the one with the more sensitive SINAD
figure if all other things were equal.

Of course, you have to trust the manufacturer to have made the
measurements accurately.  Most service shops only check the quieting
quieting when they do a repair job, since setting up for a SINAD
measurement is a pain unless you have just the right instrument.
Normally a repair that restores the quieting sensitivity will also
restore the SINAD, so most don't check.

Typical service monitors which include SINAD capability might well run
the service shop over $15,000 per instrument.  Probably only the bench
tech has one if they have one at all; the field techs usually get the
cheaper instruments.
				- Brian