chuck wrote:

Owen Duffy wrote:

On Fri, 14 Oct 2005 00:58:35 GMT, Owen Duffy wrote:



It is the ratio of signal to noise and distortion, and it is measured
by setting up a test where the receiver produces output from a SSG
(typically for a 1KHz audio output) and notching out the 1KHz output
to measure the noise and distortion wrt the filtered 1KHz output.



That should be: It is the ratio of signal and noise and distortion to
noise and
distortion, and it is measured by setting up a test where the receiver
produces output from a SSG (typically for a 1KHz audio output) and
notching out the 1KHz output to measure the unfiltered output wrt the
noise and distortion.

I should also have mentioned the EIA test requires the receiver be set
to rated output with 1mV RF input at 60% of rated modulation, then the
RF output reduced to find the input level for 12dB SINAD.

You could measure it with soething like a HP334A Distortion Analyser,
but it is pretty tedious if you are trying to find the RF input for a
particular SINAD. Hence you see boxes that have an AGC controlled
amplifier deliving a constant voltage to the filter block. I have a
Motorola one (R1013A) that works ok, there were also Sinadders. Even
more convenient are the ones integrated into a communications monitor.
I don't believe these boxes do true RMS measurements.

An alternative if you have a standalone SSG and want to do SINAD
measurement is to use a PC sound card and software that does an FFT
and calculates the SINAD (using true RMS measurement). Spectrum Lab
does it, its free, but it is such a flexible / general tool, it may be
a bit daunting to get it working. The SpectrumLab menu "Quick Settings
/ Rx Equipment Tests / SINAD test" is a quick path to setup... but it
is still a quite complex package. A whole lot better than the style of
a HP334A though! SL is at http://www.qsl.net/dl4yhf/spectra1.html .

Owen
--
Good info, Owen. I think the EIA test procedures really have FM or AM in
mind, rather than SSB or, what is exactly the same for SINAD purposes,
CW. The 60% figure just doesn't apply to SSB or CW. You would simply use
an unmodulated signal generator with the frequency offset to produce a 1
kHz tone in the receiver's audio output, preferrably centered in the
receiver's passband. Then a measure of rms af voltage at the receiver's
output with and without the 1 kHz filter would be made.

We don't hear much about SINAD testing procedures for SSB and CW. Even
the ARRL's test procedure manual glosses over the procedure for other
than FM.

Chuck
NT3G

SINAD measurements were cooked up because the audio quality of an FM
receiver depends both on the demodulator and on the noise
characteristics of it's front end. Just having a noise figure for an FM
receiver is pretty useless. Keep in mind that an FM receiver is usually
rated as "X dB SINAD for y microvolts input".

For SSB and CW, on the other hand, the noise is purely additive so all
you need to know is the receiver noise figure. Once you know that
(assuming that it's not a really strange radio) you know everything
about it's performance. Given the noise figure in dB you can easily
calculate the 12dB SINAD should you be so inclined, as well as any other
signal vs. noise figure you should want. You have a good reason to
believe that the noise is white so you can even take an SSB receiver and
calculate the noise figure of the thing after you tack on an audio
bandpass filter for CW. This is _not_ the kind of thing you could do
with FM.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com