Still not sure what it is.

I know I do a test at work where I put in a 3 KHz deviated, 1 KHz tone
into the FM receiver
port while probing an audio point going to the SINAD port on the test
equipment.
Increasing the input level makes for a larger SINAD value (which makes
sense)
Looking for at least 12 dB SINAD.
What is so special about 12?

Can't get my mind around it. Is the test tone 12 dB stronger than noise
+ distortion?

Is the the input value in dBm on the test equipment the sensitivity of
the receiver at 12 dB SINAD.
The 'at 12 dB SINAD' still gets me.

It is probably a good enough ratio to express the lower limit of
usable sensitivity for telephony applications.

If you mean why isn't it 11 or 13dB, it may hark back to the early
instruments that were intended for measuring THD and were scaled in %
distortion. 12dB SINAD corresponds to 25% distortion on such an
instrument.

Owen
--

After 36+years in the radcoms industry as a technician I have seen the
move from S/N to SINAD at first hand.

SINAD has been around throughout my career but it is really on in the
last 20 years that it has become most prevalent. The only reason that
I can think that this has become so is the improvement in technology
in the production of semiconductors and the consequent reduction in
their noise levels, and the much wider use of FETs in front ends,
which has resulted in S/N becoming an unrealistic measurement, the
noise floor now being so low. Add to this the now commonplace use of
SMD - which itself is 'quieter' - and improved circuit design, and the
distortion in the modulation becomes of significantly greater
importance.

Having said that 10% distortion was the norm when I started, whereas
2% or even less is today's standard, such are the improvements in that
side of transmission, hence SINAD is probably now the only viable
measurement.

Think of it like this: in the mid 70's most receivers would do 12dB
S/N for around 0.6uV for 60% system modulation on a 12.5KHz channel
spacing; today it is not uncommon to see 12dB SINAD (let alone S/N!)
at not much above 0.2uV, and if you look at equipments of far eastern
origin which may not have such good parameters (selectivity, adjacent
channel rejection, etc) as UK/European designed units it can be 3dB
better than that! Perhaps that's why you see a lot of oriental mobiles
and portables but most associated base stations, especially those used
on communal sites, are designed or made elsewhere (UK, USA, Germany,
and New Zealand to mention but a few.)

Why 12dB? My two penn'uth is that the human ear is very tolerant of
even harmonic distortion, especially 2nd which would predominate in
the audio chain due to filtration, so someone somewhere defined 12dB
(or about 25% distortion) as the maximum tolerable level for usable
speech.


--
Woody

harrogate2 at ntlworld dot com

In article , crb wrote:

Is the the input value in dBm on the test equipment the sensitivity of
the receiver at 12 dB SINAD.
The 'at 12 dB SINAD' still gets me.

CRB-

Years ago sensitivity might have been measured using a "20 dB quieting"
method. You would inject an unmodulated carrier and increase its level
until the noise output of the receiver decreased to one tenth of the
no-signal value. This might work for tuning to improve that one
receiver's sensitivity, but it isn't the greatest for comparing different
receivers with different bandwidths.

Isn't SINAD an acronym for "Signal In the presence of Noise And
Distortion"? I don't fully understand how it works, but assume there is a
1 KHz filter feeding one channel that is compared to an un-filtered
channel.

What I want to know is how to build one. Does anyone know of any SINAD
construction articles?

73, Fred, K4DII

Hello Fred,

If you have a calibrated RF signal generator that provides 1 kHz
modulation and an rms voltmeter that covers communication audio
frequencies (say to 3 kHz), then the only thing you need to make SINAD
measurements is a 1 kHz notch filter. You can find schematics for that
in the ARRL handbook and elsewhere.

Good luck!

Chuck
NT3G

Fred McKenzie wrote:
In article , crb wrote:


Is the the input value in dBm on the test equipment the sensitivity of
the receiver at 12 dB SINAD.
The 'at 12 dB SINAD' still gets me.


CRB-

Years ago sensitivity might have been measured using a "20 dB quieting"
method. You would inject an unmodulated carrier and increase its level
until the noise output of the receiver decreased to one tenth of the
no-signal value. This might work for tuning to improve that one
receiver's sensitivity, but it isn't the greatest for comparing different
receivers with different bandwidths.

Isn't SINAD an acronym for "Signal In the presence of Noise And
Distortion"? I don't fully understand how it works, but assume there is a
1 KHz filter feeding one channel that is compared to an un-filtered
channel.

What I want to know is how to build one. Does anyone know of any SINAD
construction articles?

73, Fred, K4DII

Let me try my hand at this...

"crb" wrote in message ...
Still not sure what it is.

I know I do a test at work where I put in a 3 KHz deviated, 1 KHz tone
into the FM receiver port while probing an audio point going to the
SINAD port on the test equipment.
Increasing the input level makes for a larger SINAD value (which makes
sense) Looking for at least 12 dB SINAD.
What is so special about 12?

Can't get my mind around it. Is the test tone 12 dB stronger than noise
+ distortion?


That's the simplest way to look at it. The desired signal (tone) is
(approximately) 12 dB above the junk.


Is the the input value in dBm on the test equipment the sensitivity of
the receiver at 12 dB SINAD.

Yep. That's it! The INPUT level, which gives this special output
condition, IS the sensitivity.


When measuring sensitivity, you need some kind of a reference point and the
signal to noise ratio at the receiver output (after a fashion) is what is
used here. . If I recall correctly, way back, AM receiver sensitivity was
the input signal (with some standard modulation) which produced the rater
power output (audio) with the volume cranked all the way up.

"Fred McKenzie" wrote in message
...
In article , crb wrote:


Years ago sensitivity might have been measured using a "20 dB quieting"
method. You would inject an unmodulated carrier and increase its level
until the noise output of the receiver decreased to one tenth of the
no-signal value. [...snip...]

Isn't SINAD an acronym for "Signal In the presence of Noise And
Distortion"? I don't fully understand how it works, but assume there is a
1 KHz filter feeding one channel that is compared to an un-filtered
channel.
What I want to know is how to build one. Does anyone know of any SINAD
construction articles?
73, Fred, K4DII

I for got about the 20 dBQ method. That's another reference for
sensitivity on FM receivers.

That's right Fred. It's explained up thread, but basically it is the ratio
of the un-notched audio to the notched audio. The "audio" is the result a
1kHz FM modulation at 60% of rated system deviation. Originally, for 5kc
ssytems dev., the 3kc deviation was 3.3kc. WHY is this at around 2/3
maximum? Well, in a well designed Tx, the deviation will get up to this
level before the deviation limiting clipper starts to clip and cause
distortion.

73, Steve

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