What is SINAD?
 

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 Thu, 13 Oct 2005 17:27:14 -0700, crb wrote:

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?

Thats about it.

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.

I wrote a handy little calculator for converting rx senstivity
metrics, it is at http://www.vk1od.net/sc/RxSensitivityCalc.htm . The
conversions assume that the signal distortion component of the
Noise+Distortion is zero, in other words that the demodulation and
amplification process is linear.

SINAD is used widely to express the sensitivity of AM, FM and SSB
receivers. It is a much better method of measuring FM receivers than
the older "quieting" measurement.

Owen
--

Does anyone happen to know where there is a circuit diagram for a home
brew SINAD meter ?

Owen Duffy wrote:
On Thu, 13 Oct 2005 17:27:14 -0700, crb wrote:


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?


Thats about it.

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.

I wrote a handy little calculator for converting rx senstivity
metrics, it is at http://www.vk1od.net/sc/RxSensitivityCalc.htm . The
conversions assume that the signal distortion component of the
Noise+Distortion is zero, in other words that the demodulation and
amplification process is linear.

SINAD is used widely to express the sensitivity of AM, FM and SSB
receivers. It is a much better method of measuring FM receivers than
the older "quieting" measurement.

Owen
--

On Fri, 14 Oct 2005 01:03:00 GMT, David wrote:

Does anyone happen to know where there is a circuit diagram for a home
brew SINAD meter ?

You should also consider searching the net for software that will use
the PC sound card to make a SINAD measurement.

Owen
--

"David" wrote in message
...
Does anyone happen to know where there is a circuit diagram for a home
brew SINAD meter ?


While not homebrew , here is where you can find a manual and schematic for a
sinad meter.

http://www.repeater-builder.com/other-mfrs/sinadd.pdf

Thanks, that's what I was after.

Ralph Mowery wrote:
"David" wrote in message
...

Does anyone happen to know where there is a circuit diagram for a home
brew SINAD meter ?



While not homebrew , here is where you can find a manual and schematic for a
sinad meter.

http://www.repeater-builder.com/other-mfrs/sinadd.pdf

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 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
--

I use Baudline (http://www.baudline.com - Linux) for doing measurements
like that. Works well.

One should calibrate the soundcard first though.

There are a host of others..

Cheers Bob VK2YQA

Owen Duffy wrote:

On Fri, 14 Oct 2005 01:03:00 GMT, David wrote:


Does anyone happen to know where there is a circuit diagram for a home
brew SINAD meter ?


You should also consider searching the net for software that will use
the PC sound card to make a SINAD measurement.

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

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
--

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

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 13:08:22 -0500, "Steve Nosko"
wrote:


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.

It was a shabby description in my first post Steve, I wrote filtered
instead of unfiltered, had the "wrt", terms back to front at the and,
as you quoted signal to (N+D) when it is the total to (N+D). Wasn't
really worth 2/10, was it! I re-read it when I came back to add some
detail re a software approach and redrafted it.

My recollection was then when the scheme was introduced, one used a
Distortion Analyser, and I can't remember the early HP instrument, the
HP334A I mentioned in my follow up was a newer one. They are tedious,
whereas the R1013 or Sinadder or much more convenient, and the
integrated ones (like in the R2000) are much better.

Once you sort the issues of getting audio samples to a PC sound card
without hum and clipping, that approach can work well, and Spectrum
Lab works well... just it is a multipurpose tool for a simple job.
There are probably other software tools that are more targetted and
simpler to use.


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

Yes, but I don't believe most of the instruments acutally incorporate
a true RMS meter. I set about measuring the difference about six
months ago when I was doing calibration / validation measurements for
FSM (http://www.vk1od.net/fsm/) using custom software against the
R1013, and R2000, and a couple of HP334As. The error in using a
rectifier-average responding meter (as is typically done) is small
relative to the variance of such readings because of the variance of
the noise component.


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.

Yes, I didn't mention that the 1KHz tone needs to be relatively low
distortion. For measuring 12dB SINAD, the demand is not onerous, but
it is important. The frequency of the tone is important as the notches
in semi automatic instruments are typically +/10Hz or so, so one needs
to verify that the SSG modulation oscillator is close enough. More
importantly when testing an SSB receiver (where you use a CW carrier),
that the carrier is kept "on frequency" for a 1KHz beat note.

Owen
--

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

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
--

Richard,

I understand the historical difficulties of making accurate RMS
measurements, however I didn't know the original post only solicited ways to
make the measurement with "current generation of commercial surplus
equipment ". My intention was to point out some measurement nuances that
might not be obvious at first glance.

Recently, it has become quite easy to do true RMS measurement at audio
frequencies using DSP techniques. In fact at audio you can even do an
accurate RMS measurement in DSP using a PIC microcontroller to sample the
signal and perform the calculations.


Joe
W3JDR


"Richard Clark" wrote in message
...
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

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.

On Sat, 15 Oct 2005 00:40:34 GMT, "W3JDR" wrote:

I understand the historical difficulties of making accurate RMS
measurements, however I didn't know the original post only solicited ways to
make the measurement with "current generation of commercial surplus
equipment ".

Hi Joe,

That was interjected by me, knowing the market of the past several
years being flooded after trunk systems began replacing older service.

My intention was to point out some measurement nuances that
might not be obvious at first glance.

Useful information, that.

Recently, it has become quite easy to do true RMS measurement at audio
frequencies using DSP techniques. In fact at audio you can even do an
accurate RMS measurement in DSP using a PIC microcontroller to sample the
signal and perform the calculations.

Yes, the miracle of Moore's law. 20 years ago I was with HP, here, to
help them introduce their 100KHz real-time dual channel audio spectrum
analyzer. That was a tremendous effort with a million lines of Pascal
code and 5 years in the making when most HP instrumentation hit the
market in 18 months from inception.

I got to know the range of FFTs under some of the most brilliant minds
on the topic. One, Nick Pendergrass, went on to teach at an eastern
university.

Today, it is an underclass topic, probably occupying no more than 6
weeks of instruction coupled to other interests. Still and all, I see
considerable errors of omission in the discussion. Such errors often
make the difference in delivering a serviceable performance compared
to that which is 100 times better (actually a million times, but few
could get their imagination around a number that big so I understate
it).

73's
Richard Clark, KB7QHC

What is SINAD?
 

"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

What is SINAD?
 

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

What is SINAD?
 

On Sat, 15 Oct 2005 00:40:34 GMT, "W3JDR" wrote:


Recently, it has become quite easy to do true RMS measurement at audio
frequencies using DSP techniques. In fact at audio you can even do an
accurate RMS measurement in DSP using a PIC microcontroller to sample the
signal and perform the calculations.

I mentioned in an earlier post that I had done some comparisons of
true RMS response based SINAD measurements and average responding
meters.

I have just rerun the test.

I have a receiver with 2400Hz wide IF , fed with SSG and connected to
a HP334A Distorion Analyser. I have adjusted the SSG for 12dB
indicated SINAD on the HP334A.

The HP334A's meter is boldly labelled RMS, but it is an average
responding meter scaled for RMS with a sine wave.

I measured the output from the HP334A using a no-name true RMS
voltmeter that covers the audio frequencies involved (trap there...
some dont make it past power frequencies), and measured SINAD of
11.3dB.

I connected the HP334A output to a PC running FSM and measured the
following figures for Vtotal and Vfiltered

total filtered
V Average 2708 679
V RMS 2753 763
V Peak 4287 2302

(The three detectors in FSM are all calibrated to read the same on a
sine wave.)

The FSM measurements indicate a SINAD of 11.1dB RMS responding and
12dB average responding.

Overall, the two / three methods are reasonably consistent indicating
around 12dB SINAD using an average response meter, and around 11.2 dB
using RMS responding meters.

That suggests to me that using an average responding instrument may
overestimate the SINAD by a little less than a dB. However, given the
statistical variance of the noise, I would not be fretting about it,
especially on an FM rx where it might only need a smaller change in
C/N for that SINAD change.

I connected the rx to a Motorola R1013A which indicated 12dB SINAD (it
is most unlikely to have an RMS responding ALC and meter).

Owen
--

What is SINAD?
 

On Mon, 17 Oct 2005 00:05:18 GMT, Owen Duffy wrote:

This is seriously bad, replying to one's own post... but.

It occurs to me a quick test to reveal whether a SINAD meter is RMS
responding or average responding is to test it with a 1KHz square
wave. I am not suggesting this as a cal procedure, just a test that is
more sensitive to the meter response than noise testing.

IIRC, the Taylor series coefficients for a square wave a all even
harmonics are 0, the others are 4/pi/n.

So, theoretically:
- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;
- an ideal RMS responding meter should read
(1-(2^-0.5*4/PI())^2)^0.5*100% which is 43.5% or 7.23dB.

Does the maths make sense?

I observe that my R1013A indicates 9dB on a good square wave, and the
HP334A around 35% (9.1dB)... so another indication that they are
average responding. I expect the readings a little low because neither
instrument has infinite bandwidth.

Owen
--

What is SINAD?
 

On Mon, 17 Oct 2005 03:09:11 GMT, Owen Duffy wrote:


So, theoretically:
- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;

I think this is close to the right answer, but for the wrong reason. I
think it needs to be evaluated iteratively, and I get an answer closer
to 34.3% or 9.3dB.

Owen
--

What is SINAD?
 

Hello Owen,

Seems both average-responding and trms meters use rectifiers, so a
square wave input with perfect symmetry should result in BOTH meters
reading the same: an amount equal to the peak square wave voltage. Am I
confused on this?

Chuck

Owen Duffy wrote:
On Mon, 17 Oct 2005 03:09:11 GMT, Owen Duffy wrote:



So, theoretically:
- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;


I think this is close to the right answer, but for the wrong reason. I
think it needs to be evaluated iteratively, and I get an answer closer
to 34.3% or 9.3dB.

Owen
--

What is SINAD?
 

"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

What is SINAD?
 

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

Owen, (& crb)
Your words are contrary to the way we measured it (Motorola). ...

It was a shabby description in my first post Steve, ...with considerable
clarification...

Yes, I didn't mention that the 1KHz tone needs to be relatively low
distortion. ...
frequency of the tone is important as the notches
in semi automatic instruments are typically +/10Hz or so, ...
Owen


Not only that, but 1kHz is important because it is the standard and
usiang another freq, say 2kHz puts is on another part of the de-emphasis
curve and numbers'll change.
73, Steve, K,9.D;C'I

What is SINAD? Qiock test
 

"Owen Duffy" wrote in message
...
On Mon, 17 Oct 2005 00:05:18 GMT, Owen Duffy wrote:

This is seriously bad, replying to one's own post... but.

It occurs to me a quick test to reveal whether a SINAD meter is RMS
responding or average responding is to test it with a 1KHz square
wave. I am not suggesting this as a cal procedure, just a test that is
more sensitive to the meter response than noise testing.

IIRC, the Taylor series coefficients for a square wave a all even
harmonics are 0, the others are 4/pi/n.

So, theoretically:
- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;
- an ideal RMS responding meter should read
(1-(2^-0.5*4/PI())^2)^0.5*100% which is 43.5% or 7.23dB.

Does the maths make sense?



Wait a minute here. You're percents and dB is confusing.

I don't know about the 1-2/pi. It's been about a year or so since I went
through all this for that QST article using a serise resistor in the power
line to figure out power supply (and rig) power consumption - unfortunately
ignoring the pulsed nature of capacitor input power supply current,
BUT...

I don't remember the analytical expressions for these quantities. I'll use
the common numbers...

For the meter that responds to average (63% peak - I think this is 2/pi) ,
but shows RMS which is .707 of peak (1/root2), the ratio for average input
to reading = 0.707/.63 . For this I get 2/(2* root2)

Average of a square wave is equal to the peak.

So a 1 volt (pk) square wave should measure 1.11 Volts on one of these (sine
average responding, RMS displaying) meters and 1V on an rms meter.

I think I did that right?

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

What is SINAD?
 

Nope. See my previous post.


A square wave has an average equal to the RMS equal to the peak. It's just
like DC.

The "older types" RESPOND to average of a SINE (63% of peak) but display the
value for the RMS (71% of peak), so they have a 1.11 correction factor to
get from average to RMS.

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


"chuck" wrote in message
ink.net...
Hello Owen,

Seems both average-responding and trms meters use rectifiers, so a
square wave input with perfect symmetry should result in BOTH meters
reading the same: an amount equal to the peak square wave voltage. Am I
confused on this?

Chuck

Owen Duffy wrote:
On Mon, 17 Oct 2005 03:09:11 GMT, Owen Duffy wrote:



So, theoretically:
- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;


I think this is close to the right answer, but for the wrong reason. I
think it needs to be evaluated iteratively, and I get an answer closer
to 34.3% or 9.3dB.

Owen
--

What is SINAD?
 

On Mon, 17 Oct 2005 16:39:25 GMT, chuck wrote:

Hello Owen,

Seems both average-responding and trms meters use rectifiers, so a
square wave input with perfect symmetry should result in BOTH meters
reading the same: an amount equal to the peak square wave voltage. Am I
confused on this?

Leaving aside the rectifier point which is arguable:

If we accept that the RMS responding instrument reads correctly on all
types of waveforms, the issue is with the average responding
instrument.

The average responding instrument is (usually) calibrated for the form
factor of a sine wave, and its scaling in RMS is only valid for
waveforms with the same form factor.

There are two cases to consider, the square wave, and the square wave
with the fundamental removed. The form factor of both are different to
the form factor of a sine wave, and more importantly to each other, so
the average responding meter does not provide an accurate ratio of the
(true) power of each wave.

Does that make sense?

Owen
--

What is SINAD?
 

"chuck" wrote in message
link.net...
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

Thanks Chuck, forgot all about RSS 181, even though I have type approval
tested countless SSB transceivers to that specification. Interesting that
it has not been updated since 1971. Note that he sensitivity is defined as
that input that will produce 12 dB SINAD or that input which will produce at
least 50% of the rated audio output. The fact is that most of the testing
that I did was measured at full audio output, just below the threshold of
audio clipping. I do not recall any unit where the receiver gain was a
factor in sensitivity. Also note they still refer to "A3j", and not J3E,
etc. All these old specifications are based on tube designs. With TDA2002
type audio chips, you could typically get 5W out at 1% distortion. It was
so easy to drop in an extra IF stage if you could not meet the 50% min audio
output at threshold sensitivity.

73,

Frank

What is SINAD?
 

You're correct, of course, Steve. I was thinking the average-responding
meter was calibrated to display average levels, but it is not: it is
calibrated to give the rms value of a true sine wave with that average
value. So the only way to measure the average value of a non-sinusoidal
ac signal is to use an average-responding meter and correct the
displayed reading as you have noted. Not relevant to the SINAD
discussion but interesting.

Thanks for the clarification.

Chuck

Steve Nosko wrote:
Nope. See my previous post.


A square wave has an average equal to the RMS equal to the peak. It's just
like DC.

The "older types" RESPOND to average of a SINE (63% of peak) but display the
value for the RMS (71% of peak), so they have a 1.11 correction factor to
get from average to RMS.

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


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

Hello Owen,

Seems both average-responding and trms meters use rectifiers, so a
square wave input with perfect symmetry should result in BOTH meters
reading the same: an amount equal to the peak square wave voltage. Am I
confused on this?

Chuck

Owen Duffy wrote:

On Mon, 17 Oct 2005 03:09:11 GMT, Owen Duffy wrote:




So, theoretically:
- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;


I think this is close to the right answer, but for the wrong reason. I
think it needs to be evaluated iteratively, and I get an answer closer
to 34.3% or 9.3dB.

Owen
--

What is SINAD? Qiock test
 

On Mon, 17 Oct 2005 14:01:41 -0500, "Steve Nosko"
wrote:


"Owen Duffy" wrote in message
.. .
On Mon, 17 Oct 2005 00:05:18 GMT, Owen Duffy wrote:


- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;

In another post ) I have
identified that that expression is wrong.

The correct ratios are closer to 34.3% or 9.3dB.


Wait a minute here. You're percents and dB is confusing.

Many Distortion analysers are calibrated in % where the % figure is a
voltage ratio.


I don't know about the 1-2/pi. It's been about a year or so since I went

It is wrong, see above.

through all this for that QST article using a serise resistor in the power
line to figure out power supply (and rig) power consumption - unfortunately
ignoring the pulsed nature of capacitor input power supply current,
BUT...

I don't remember the analytical expressions for these quantities. I'll use
the common numbers...

For the meter that responds to average (63% peak - I think this is 2/pi) ,
but shows RMS which is .707 of peak (1/root2), the ratio for average input
to reading = 0.707/.63 . For this I get 2/(2* root2)

Average of a square wave is equal to the peak.

So a 1 volt (pk) square wave should measure 1.11 Volts on one of these (sine
average responding, RMS displaying) meters and 1V on an rms meter.

I think I did that right?

The problem is that while the RMS meter provides a true power
indication on the square wave, and the filtered square wave (ie
without fundamental), the average responding meter does not give an
accurate power ratio because the form factors (RMS/AVG) of the two
waveforms is different.

Owen
--

What is SINAD?
 

On Mon, 17 Oct 2005 05:09:06 GMT, Owen Duffy wrote:

On Mon, 17 Oct 2005 03:09:11 GMT, Owen Duffy wrote:


So, theoretically:
- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;

I think this is close to the right answer, but for the wrong reason. I
think it needs to be evaluated iteratively, and I get an answer closer
to 34.3% or 9.3dB.

An analytical approach to solution of the problem.

A unit height square wave has a fundamental component of amplitude
4/pi.

To find the area under the filtered curve, I think we are looking for
the integral from 0 to pi/2 of absolute(1-4/pi*sin(theta))). I will
divide the integral at theta=asin(pi/4) to deal with the absolute
function since the problem function is positive from 0 to asin(pi/4)
and negative from asin(pi/4) to pi/2.

Here is some Perl to evaluate the ratio:

#find the zero crossing point
$theta=asin($pi/4);
#find the area under the curve
$area=$theta-4/$pi*(-cos($theta)+cos(0)); #first part
$area+=4/$pi*(-cos($pi/2)+cos($theta))-($pi/2-$theta); #second part
#divide by area under unit square wave
$ratio=$area/($pi/2);
print "Average response ratio is $ratio \n";

And the answer is 0.3430678471... or 9.3dB. It is about 9.4dB if you
only consider the harmonics up to 50KHz.

One of you mathematical whizzes might know a better way to put this!

Owen
--

What is SINAD?
 

Owen,

[[[ while I suspect the difference is so small that it makes little
difference in the receiver sensitivity number arrived at, I proceed
anyway. ]]


From your last two posts, it appears you/we have vastly different
interpretations of what the question was. You talk about removing the
fundamental from the square wave and this puzzles me. I do not believe the
intent was to measure SINAD using a square wave modulation. Therefore
removing its fundamental and measuring its RMS does not fit the situation.


My understanding of the issue was measuring SINAD with the older
"Average-measuring-, RMS-reading" type (call it the "AVG-Type") of meter vs,
a "true RMS" reading meter.

While I did talk about measuring a square wave with the "AVG_Type" meter,
that was a digression only ment to show (what I think is) the difference for
the previously proposed reference measurement. Namely try simply measuring
a square wave for comparing the two meter readings, not SINAD measurements.
I did this to show a calculation of how the two meters would read knowing
the average and RMS values of _some_ waveform. I was thinking that I could
do this for the two SINAD waveforms, but as you see here, I gave up...

Back to SINAD.
Therefore, the issue I was addressing was the following:
(for the normal SINAD technique, 1 kHz sine wave tone):
A- Assume the RMS meter gives the "correct" reading.
B- What does the "AVG_Type" show on the display/scale?

So, B has two parts.

1- What does the "AVG-Type" read for the un-notched signal, and
2- What does the "AVG-Type" show for the notched signal.

1- As a first approximation, lets say the un notched reading is dominated by
the sine wave. With this assumption, they both read the same. To refine
this estimate, I am unable to assess, easily, the effect of the noise on
either measurement except that the True RMS mwter will give an indication of
the total tone and noise power (actually Erms^2). As a first approximation,
we could say that the "AVG-Type" reads the average of the sine plus the
average of the noise voltages...and my estimation powers peter-out right
there.
2- What does the "AVG_Type" read on the noise (notched signal)... yep, peter
once again.

Therefo

GOTO [[ my statement in brackets above ]]



Then there's the pronunciation. Some say "sin' add" and some say "sign'
add". We said SIN add.

Nice exercise, time for me to move on to other things.

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


"Owen Duffy" wrote in message
...
On Mon, 17 Oct 2005 05:09:06 GMT, Owen Duffy wrote:

On Mon, 17 Oct 2005 03:09:11 GMT, Owen Duffy wrote:


So, theoretically:
- an ideal average responding meter should read (1-2/pi)% which is
36.3% or 8.8dB on an perfect square wave;

I think this is close to the right answer, but for the wrong reason. I
think it needs to be evaluated iteratively, and I get an answer closer
to 34.3% or 9.3dB.

An analytical approach to solution of the problem.

A unit height square wave has a fundamental component of amplitude
4/pi.

To find the area under the filtered curve, I think we are looking for
the integral from 0 to pi/2 of absolute(1-4/pi*sin(theta))). I will
divide the integral at theta=asin(pi/4) to deal with the absolute
function since the problem function is positive from 0 to asin(pi/4)
and negative from asin(pi/4) to pi/2.

Here is some Perl to evaluate the ratio:

#find the zero crossing point
$theta=asin($pi/4);
#find the area under the curve
$area=$theta-4/$pi*(-cos($theta)+cos(0)); #first part
$area+=4/$pi*(-cos($pi/2)+cos($theta))-($pi/2-$theta); #second part
#divide by area under unit square wave
$ratio=$area/($pi/2);
print "Average response ratio is $ratio \n";

And the answer is 0.3430678471... or 9.3dB. It is about 9.4dB if you
only consider the harmonics up to 50KHz.

One of you mathematical whizzes might know a better way to put this!

Owen
--

What is SINAD?
 

On Tue, 18 Oct 2005 10:37:15 -0500, "Steve Nosko"
wrote:

Owen,


From your last two posts, it appears you/we have vastly different
interpretations of what the question was. You talk about removing the
fundamental from the square wave and this puzzles me. I do not believe the
intent was to measure SINAD using a square wave modulation. Therefore
removing its fundamental and measuring its RMS does not fit the situation.


Some discussion arose about the extent of errors when using an aveage
responding meter to measure SINAD (compared to a true RMS meter).

My experimental evidence is that when measuring SINAD on a 2.4KHz wide
receiver at SINAD=12dB, the error is less than 1dB. Of course, it will
be less for higher SINAD ratios, and worse for lower ones.

I offered that a simple test of whether a SINAD meter was average
responding or true RMS responding, was to measure the SINAD of a good
square wave. The average responding meter will indicate about 9.3dB
whereas an RMS responding meter will indicate around 7.3dB.

I think we both understood that.


Back to SINAD.
Therefore, the issue I was addressing was the following:
(for the normal SINAD technique, 1 kHz sine wave tone):
A- Assume the RMS meter gives the "correct" reading.
B- What does the "AVG_Type" show on the display/scale?

So, B has two parts.

1- What does the "AVG-Type" read for the un-notched signal, and
2- What does the "AVG-Type" show for the notched signal.

1- As a first approximation, lets say the un notched reading is dominated by
the sine wave. With this assumption, they both read the same. To refine
this estimate, I am unable to assess, easily, the effect of the noise on
either measurement except that the True RMS mwter will give an indication of
the total tone and noise power (actually Erms^2). As a first approximation,
we could say that the "AVG-Type" reads the average of the sine plus the
average of the noise voltages...and my estimation powers peter-out right
there.
2- What does the "AVG_Type" read on the noise (notched signal)... yep, peter
once again.

As I stated above, and you stated, the comparison will depend on the
extent to which the sine wave dominates the total signal, and so will
depend on the SINAD being measured. I suggest that it will also depend
on the noise bandwidth.

Repeating, my experimental evidence is that when measuring SINAD on a
2.4KHz wide receiver at SINAD=12dB, the error is less than 1dB.

At the end of the day, it doesn't matter that much for normal
applications if the SINAD meter is average responding, they appear to
overestimate the SINAD, but by a very small amount.


Therefo

GOTO [[ my statement in brackets above ]]


You are trying to send Wes in a loop.

Then there's the pronunciation. Some say "sin' add" and some say "sign'
add". We said SIN add.

Dangerous territory, this could become an international incident when
you bring pronunciation into scope. There, and you all (mostly)
thought I didn't know how to spell... all those esses where they
should be zeds, no thats zees isn't it.

Owen
--

What is SINAD?
 

"Owen Duffy" wrote in message
...
On Tue, 18 Oct 2005 10:37:15 -0500, "Steve Nosko"
wrote:

[...]

I offered that a simple test of whether a SINAD meter was average
responding or true RMS responding, was to measure the SINAD of a good
square wave. The average responding meter will indicate about 9.3dB
whereas an RMS responding meter will indicate around 7.3dB.

I think we both understood that.

Nope, I missed that concept. Thanks for the clarify.