On Fri, 14 Oct 2005 10:50:03 -0700, Tim Wescott
wrote:


bandpass filter for CW. This is _not_ the kind of thing you could do
with FM.

Indeed Tim. The complications as I see it in predicting the SINAD for
FM when you know the receiver NF is that most narrow band
communications applications of FM are closer to PM because of the
pre-emphasis characteristic.

FM + 6dB/octave preemphasis over the entire modulation passband is PM.
(PM is where the modulation index (dev/fm) is independent of fm (the
modulating frequency)).

However, the receivers in my experience are over de-emphasised (at the
top end) presumably to get better SINAD. In fact, I think
specifications of the de-emphasis curve are commonly stated along the
lines of +1 to -3dB of -6dB demphasis relative to 1Khz over 300 to
3000Hz. This accomodates a over de-emphasis at the high end for little
loss in intelligibility and a dB or so improvement in sensitivity
figures.

Filter / demodulators and CTCSS IM also contribute to distortion
products significantly.

The result of demod distortion, PM with a slope across the passband,
and uncertain high pass filtering to accomodate CTCSS makes prediction
of S/N out from C/N in a bit of a guess in FM comms receivers, not
nearly as accurate as you suggest for linear receivers.

Owen
--

Originally, two way shops set FM rigs up for 20 dB quieting, on a volt
meter (crank up the signal until the AUDIO VOLTAGE, UNMODULATED, was
1/10th the voltage of a no signal audio output . Tho, for the most
part, this works well, there are constraints on sensitivity, because of
bandwidth concerns, and , as bandwidth is halved, the signal improvement
is 6 dB (quadrupled). Sinad is Signal/Noise /signal/(noise+distortion)
and in fact, in recent times , devices that will measure it are built
into many pieces of test equipment (IFR meters comes to mind), also
look for an outfit called "SINADDER" . The main thing is that it adds
a "Bandwidth" component to the sensitivity equasion. It is measured
with a 1 KHz tone, at (in FM), 3 KHz deviation- and the smaller the
signal that is detectable , with this constraint, the more sensitive
the reciever is considered to be! This also works at SSB/AM. Tho, it
is true that this measures Sensitivity, it includes a BANDWIDTH
component, that a (noise figure/ quieting) would NOT consider (at least
fully!) Hopefully, this is helpful-- Jim NN7K


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.

"chuck" wrote in message
ink.net...
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.

The old Canadian Department of Communications Document RSS 125 Issue 1,
Released August 1st, 1976, precisely describes the method of SINAD
measurements for SSB equipment. In the past 25 years or so, HP's distortion
analyzers (such as the HP8903B) were used for this measurement. In the late
60s and early 70s I have seen Heathkit distortion analyzers used for SINAD
measurements. The latest versions of RSS125 seem to be more in line with
FCC standards, where receiver specifications are not required for
certification purposes (See
http://www.agiletestgroup.com/ICCertifications.html).

73,

Frank

Thanks for the info, Frank.

Actually, the RSS125 on the site doesn't contain the procedure, but
RSS181, also available at that site, does.

FWIW, the procedure is basically what has been discussed, except that
the signal generator output to be recorded as the receiver's sensitivity
is that level which produces a 12 dB SINAD at 50% of rated audio output!
Probably a more realistic test than allowing the AF stage to operate at
a low-distortion level of something like 1% of rated output.

73,

Chuck
NT3G


Frank wrote:


The old Canadian Department of Communications Document RSS 125 Issue 1,
Released August 1st, 1976, precisely describes the method of SINAD
measurements for SSB equipment. In the past 25 years or so, HP's distortion
analyzers (such as the HP8903B) were used for this measurement. In the late
60s and early 70s I have seen Heathkit distortion analyzers used for SINAD
measurements. The latest versions of RSS125 seem to be more in line with
FCC standards, where receiver specifications are not required for
certification purposes (See
http://www.agiletestgroup.com/ICCertifications.html).

73,

Frank

It is the ratio of (Signal + Noise+Distortion) to (Noise+Distortion) as
measured at the receiver audio output. It is measured using an RMS-reading
AC voltmeter , typically with a 1Khz modulation tone on the signal applied
to the receiver under test.

First you measure the audio signal out of the receiver using the AC RMS
meter. Then you apply a notch filter at the modulation frequency and measure
the residual noise+distortion, again using the RMS AC voltmeter. SINAD is
the ratio of the two measurements.

Joe
W3JDR



"crb" wrote in message ...
Is it only valid for AM and FM measurements?

I know its receiver sensitivity.

Is it Signal divided by Noise with distortion??

12 dB SINAD means what? The signal is 12 dB greater than noise and
distortion or
is it more complicated than that?

Owen, (& crb)
Your words are contrary to the way we measured it (Motorola). You say
...."It is the ratio of signal to noise and distortion,..", but we measured
not just the signal, but everything for the "top" of the ratio (which is
used more like a reference as it is the more stable as signal level varies).
I believe your last line saying wrt to the filtered tone supports this. It
implies that the tone is (bandpass) filtered for one of the measurements and
we don't do that.

Joe's is a bit better of an explanation (the RMS meter and quantities
ratioed).

A meter, a pure 1kHz tone modulated signal generator and a 1kHz notch is all
that is needed. What happens if you don't have a "real" RMS meter? I don't
know.

73, Steve, ,K.9;D'C'I



"W3JDR" wrote in message
news:ljM3f.39197$q81.11651@trnddc06...
It is the ratio of (Signal + Noise+Distortion) to (Noise+Distortion) as
measured at the receiver audio output. It is measured using an RMS-reading
AC voltmeter , typically with a 1Khz modulation tone on the signal applied
to the receiver under test.

First you measure the audio signal out of the receiver using the AC RMS
meter. Then you apply a notch filter at the modulation frequency and
measure
the residual noise+distortion, again using the RMS AC voltmeter. SINAD is
the ratio of the two measurements.

Joe
W3JDR



"crb" wrote in message
...
Is it only valid for AM and FM measurements?

I know its receiver sensitivity.

Is it Signal divided by Noise with distortion??

12 dB SINAD means what? The signal is 12 dB greater than noise and
distortion or
is it more complicated than that?

On Fri, 14 Oct 2005 13:08:22 -0500, "Steve Nosko"
wrote:

A meter, a pure 1kHz tone modulated signal generator and a 1kHz notch is all
that is needed. What happens if you don't have a "real" RMS meter? I don't
know.

Hi Steve,

You don't need a "real" RMS meter. The expressed requirement for a
pure 1kHz tone provides the necessary sine wave shape such that it
simply becomes a matter of scale calibration. If you had said a
square wave 1KHz tone (nothing pure about that), then you would have
to dig deep for a "real" RMS meter. That too, could be scaled, but I
wouldn't count on it because it would be a rare amplifier chain that
could faithfully keep it square - and the notch would inject it into
the measurement as distortion and noise.

73's
Richard Clark, KB7QHC

Richard,
What you said is largely accurate, however at low S/N ratios, or where the
distortion becomes comparable to the signal level, the reading of the
composite signal (signal+noise+distortion) with anything other than an RMS
meter could produce erroneous results.

Joe
W3JDR

"Richard Clark" wrote in message
...
On Fri, 14 Oct 2005 13:08:22 -0500, "Steve Nosko"
wrote:

A meter, a pure 1kHz tone modulated signal generator and a 1kHz notch is
all
that is needed. What happens if you don't have a "real" RMS meter? I
don't
know.

Hi Steve,

You don't need a "real" RMS meter. The expressed requirement for a
pure 1kHz tone provides the necessary sine wave shape such that it
simply becomes a matter of scale calibration. If you had said a
square wave 1KHz tone (nothing pure about that), then you would have
to dig deep for a "real" RMS meter. That too, could be scaled, but I
wouldn't count on it because it would be a rare amplifier chain that
could faithfully keep it square - and the notch would inject it into
the measurement as distortion and noise.

73's
Richard Clark, KB7QHC

On Fri, 14 Oct 2005 20:28:17 GMT, "W3JDR" wrote:

Richard,
What you said is largely accurate, however at low S/N ratios, or where the
distortion becomes comparable to the signal level, the reading of the
composite signal (signal+noise+distortion) with anything other than an RMS
meter could produce erroneous results.

Hi Joe,

In the practical world of SINAD (having tuned a number of GE and
Motorolas), one is not very interested in how poor your set is, but
rather meeting a service standard (that 12 dB which is as arbitrary as
any).

I doubt if many of the current generation of commercial surplus
equipment comes with a stock tester employing what would have been an
expensive converter chip to insure RMS measurements. I come by that
assessment by noting those I used employed standard meter movements.
The first RMS meters I calibrated in the mid 70s came from Fluke (just
up the highway), and the components of that circuit were scrubbed of
all identification numbers or cast in epoxy. Such was the cachet of
being hi-priced, and having others try to break into the market with
knock-offs.

My Radio Shack multimeter makes that claim (ca 1995) and if memory
serves, that Micronta's "True RMS" was barely capable of poor voice
grade bandwidth. This was 20 years after Fluke, costing about as much
(economic inflation), and not performing as well (technical
deflation).

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Fri, 14 Oct 2005 13:08:22 -0500, "Steve Nosko"
wrote:

A meter, a pure 1kHz tone modulated signal generator and a 1kHz notch is
all
that is needed. What happens if you don't have a "real" RMS meter? I
don't
know.

Hi Steve,

You don't need a "real" RMS meter. The expressed requirement for a
pure 1kHz tone provides the necessary sine wave shape such that it
simply becomes a matter of scale calibration. If you had said a
square wave 1KHz tone (nothing pure about that), then you would have
to dig deep for a "real" RMS meter. That too, could be scaled, but I
wouldn't count on it because it would be a rare amplifier chain that
could faithfully keep it square - and the notch would inject it into
the measurement as distortion and noise.

73's


Hi Richard,

I don'r know about that. For the un-notched signal, yes, where the
dominant component is the sine wave. However, not knowing how a non-RMS
meter may respond to the notched-out (predomanantly noise) signal, I'd thing
there is a possible cause for error compared to an RMS meter.
73, Steve, K,9.D;C'I