Agilent App Note says:

Tangential sensitivity is the lowest input signal power level for which the
detector will have an 8 dB signal-to-noise ratio at the output of a test
video amplifier.

http://www.home.agilent.com/upload/c...orOverview.pdf

Bill W0IYH

"W3JDR" wrote in message
news:UUo3h.2525$qJ6.2375@trndny07...
So it's not a "mathematical fact" in the sense that any of us can look it
up and see how it was derived, it's your recollection of something you
heard and vaguely remember convincing yourself it could be true, right?

While we're at it, what's the significance of your reference to "8.5 db
( tangential sensitivity)"?

Joe
W3JDR





"AndyS" wrote in message
oups.com...

W3JDR wrote:


Can you point us to a reference document that explains this
"mathematical
fact"?.

Joe
W3JDR

Andy writes:

No. It was about 25 years ago when I was designing the TI2100 FM
Marine
Transceiver for Texas Intruments, which was my last commercial Fm
unit. ( Some two meter stuff since then as home projects, tho )

It was info gleaned from several technical papers and I don't for
the
life of me remember which ones. I got a limiter and noise source
and checked it in the lab, at the time, and it seemed consistent.
I don't remember exactly, but I think I combined noise with a
signal and amplified the hell out of it, and then put in an
attenuator to get it back down and measured the S/n in a receiver.
Then I put a limiter in between the amp and the attenuator, and
decreased the atten to get the same level into the receiver, and
measured the S/N again. While I didn't get exactly 5.6 db, I
remember it was close enough to believe that the mathematical
derivation was confirmed ( in my mind ) and that my measurement
error was probly due to my own imprecision in the experiment..
Anyway, I moved on..... and it settled the question on whether
hard limiting "improves" things.....



Sorry, but that's just one of the numbers that stay with a guy, like
-174 dbm (God's noise) , and 8.5 db ( tangential sensitivity), and
10Log(bw), and 3.14..... Heck, I forget my phone number from time
to time, but numbers that I have used for most of my life stay with
me.....

And, being in the profession, I have, at some time or another,
verified
them myself in the lab when the opportunity permitted.. I take that
back.... I have never verified PI....... I hope I haven't been too
gullible..... :)))

So, I regret not having the mental acuity any more to jot down some
derivations for you. But , if they are not correct, there's a lot of
products
on the market which I built whose development was a wild fluke....

If you want to pursue it yourself, I would suggest a few texts that
have guided me... Skolnik's Radar Handbook ( the smal one, not
the BIG one --- I call it " small Skolnik" ) has a LOT of tech info
that
is presented in a level only slightly greater than the ARRL handbook.
Also "Principles of FM" -- damn, I don't remember the author.....but
how many could there be ? :)))) I might have it in my workshop.
If I run across it I'll post it here.

Well, good luck. Some knowledge can be passed on as a proven
fact and one needs look no farther..... like PI, for instance... Other
is in conflict with what someone thinks to be "how things work", and
doubt
is in the air.... No matter -- I was the same way, when I had the
energy to pursue it.....

Good on ya' , mate,

Andy W4OAH in Eureka, Texas

William E. Sabin wrote:
Agilent App Note says:

Tangential sensitivity is the lowest input signal power level for which the
detector will have an 8 dB signal-to-noise ratio at the output of a test
video amplifier.

http://www.home.agilent.com/upload/c...orOverview.pdf

Bill W0IYH


Andy writes:

I used 8.5 db, tho , as you know, it has a LOT to do with who is
making the measurement and positioning the pulse on the scope....
I'm not sure that I am proficient enough to position an 8db pedestal
to within a half db accuracy...... Agilent probly used a math
derivation.
I have seen it called out at several numbers, tho 8.5 is the one I
always used....

I will probly start using 8 db if the Agilent App note says so since
there is always somebody wanting to get a "reference", and it's
much easier to just give them the App Note source than try to
explain....
Once they actually see the scope presentation, they will understand
the problem...
Andy in Eureka

W3JDR wrote:
So it's not a "mathematical fact" in the sense that any of us can look it up
and see how it was derived, it's your recollection of something you heard
and vaguely remember convincing yourself it could be true, right?


Andy replies:
That's right. But just because I don't remember how to derive it,
or can
give you the name of the paper that I read 25-30 years ago, it doesn't
mean it's wrong. So I would suggest you do your own research....

Whether it is true, or not true, IS a mathematical fact, and if you
are
capable of understanding the math proof, you are probably also
capable of proving or disproving it yourself on paper. Me, hell , I
always
had a good lab where I could try things out if I had doubt.....

It is probly easier, if you have access to a good lab, to rig up an
experiment to find out..... That way you wouldn't have to bother with
newsgroups to learn about this stuff.....

I would encourage you to try. If you come up with a good answer you
can be proud of, post it back here for us all to see. I am sure many
people here would be interested , since lots of time is often wasted
coming up with circuits whose purpose is doomed from the start....
such as using "hard limiters" to improve the SNR........

As far as the "tangential sensitivity", you can probly do a google
search and learn all about it.... If you haven't run into it yet, you
probably don't deal with OOK pulses like radar and stuff. There's no
shame in that.....

:)))) Andy in Eureka, Texas W4OAH

Andy writes

Well, I saved you some time by googling it myself. It took about 10
seconds
to be able to cut and paste the definition I have been talking
about....

Note that in this paper it says TSS is eight db +/- one db ....
and depends on several system factors, including the
actual detector used... From experience, the detector type,
and the absolute signal level it is detecting, is a BIG DEAL.
It needs to operate in the "perfect diode" region . Doing the
detection in the square law region buggers up the measurement.

That +/- one db is due to the accuracy that one operator can set up
the
scope versus the next operator that comes along. I use 8.5 db, and
I DARE anyone to set the same measurement up 10 times in a row and
get the same answer to less than +/- one db.

Agilent probly uses a math derivation to get 8 db to accomplish
some specific criteria, and did not specify a detector type, hence
it is a "mathematically perfect " answer. Furthermore, they use a
different
definition, but ORIGINALLY it was bases on the FIRST SENTENCE in
the cut and paste below...

The Agilent App Note that Bill Sabin refers to also came up on the
first page of hits, and you can go read it for yourself.

I hope this satisfies your curiousity. I had nothing better to do
today..... Now, I'm outta beer, and Jeff Foxworthy is on TV,
so 73s

Andy W40AH


***********CUT AND PASTE FROM GOOGLE HIT *************************

TANGENTIAL SENSITIVITY
Tangential sensitivity (TSS) is the point where thetop of the noise
level with no signal applied is level with thebottom of the noise level
on a pulse as shown in Figure 6.

Itcan be determined in the laboratory by varying the amplitudeof the
input pulse until the stated criterion is reached, or byvarious
approximation formulas.The signal power is nominally 8±1 dB above
thenoise level at the TSS point. TSS depends on the RFbandwidth, the
video bandwidth, the noise figure, and the detector characteristic.

TSS is generally a characteristic associated with receivers (or RWRs),
however the TSS does not necessarilyprovide a criterion for properly
setting the detection threshold. If the threshold is set to TSS, then
the false alarm rate israther high.

Radars do not operate at TSS. Most require a more positive S/N for
track ( 10 dB) to reduce false detectionon noise spikes.
SENSITIVITY CONCLUSION
When all factors effecting system sensitivity are considered, the
designer has little flexibility in the choice ofreceiver parameters.
Rather, the performance requirements dictate the limit of sensitivity
which can be implemented by theEW receiver.1. Minimum Signal-to-Noise
Ratio (S/N) - Set by the accuracy which you want to measure signal
parameters and by thefalse alarm requirements.2. Total Receiver Noise
Figure (NF) - Set by available technology and system constraints for RF
front end performance.3. Equivalent Noise Bandwidth (B ) - Set by
minimum pulse width or maximum modulation bandwidth needed
toNaccomplish the system requirements. A choice which is available to
the designer is the relationship of pre- (B ) and post-IFdetection (B )
bandwidth. The most affordable approach is to set the post-detection
filter equal to the reciprocal of theVminimum pulse width, then choose
the pre-detection passband to be as wide as the background interference
environmentwill allow. Recent studies suggest that pre-detection
bandwidths in excess of 100 MHz will allow significant loss of
signalsdue to "pulse-on-pulse" conditions. 4. Antenna Gain (G) - Set by
the needed instantaneous FOV needed to support the system time to
intercept requirements.

*****************END OF CUT AND PASTE
***********************************

There are so many variables and approximations involved that it would seem
difficult to be very precise about 8.0 or 8.5 dB S/N ratio or some other
number. The decision probably involves the type of signal involved. 8.0 dB
in one application gives the minimum acceptible performance for one kind of
signal. A more critical system might want more than 8.0 dB to achieve a
better bit error rate, for example.

Bill W0IYH

"AndyS" wrote in message
oups.com...

William E. Sabin wrote:
Agilent App Note says:

Tangential sensitivity is the lowest input signal power level for which
the
detector will have an 8 dB signal-to-noise ratio at the output of a test
video amplifier.

http://www.home.agilent.com/upload/c...orOverview.pdf

Bill W0IYH


Andy writes:

I used 8.5 db, tho , as you know, it has a LOT to do with who is
making the measurement and positioning the pulse on the scope....
I'm not sure that I am proficient enough to position an 8db pedestal
to within a half db accuracy...... Agilent probly used a math
derivation.
I have seen it called out at several numbers, tho 8.5 is the one I
always used....

I will probly start using 8 db if the Agilent App note says so since
there is always somebody wanting to get a "reference", and it's
much easier to just give them the App Note source than try to
explain....
Once they actually see the scope presentation, they will understand
the problem...
Andy in Eureka

William E. Sabin wrote:
There are so many variables and approximations involved that it would seem
difficult to be very precise about 8.0 or 8.5 dB S/N ratio or some other
number. The decision probably involves the type of signal involved. 8.0 dB
in one application gives the minimum acceptible performance for one kind of
signal. A more critical system might want more than 8.0 dB to achieve a
better bit error rate, for example.

Bill W0IYH

Andy comments:

Yeah, .... the way I used it was to adjust the level to tangential,
then increase
the signal level with an attenuator to get the S/n I wanted,,,,,

You know how hard it is to put together the stuff to measure the
S/N of a pulsed signal ? Well, by setting it up to get 'tangential"
then
messing with the attenuators to get what I wanted, I could, with
reasonable
accuracy, set up a measurement for 13 o 14 db S/n , or whatever, to
take
the Pfa measurement....

( Those are the S/N levels that reasonable Pfa and Pd numbers occur )


Remember, Tangential Sensitivity was defined 50 years before
Agilent
was in existence... Maybe more....... It allowed a person with a scope
to
make reasonably accurate measurements, and refine their systems to take
advantage of it, 50 years before the simulators, and math, dealt
conclusively
with the issue. Hewlitt was using light bulbs to make audio
oscillators when
RADAR engineers were finding German airplanes....

If my use of the HISTORICAL term has confused these kids that just
got
their BSEE,...... I don't really care....

Why do we respond to these kids ? Probably because we both are
retired and bored.....If they want to prove we are stupid, ...
hell,.... it's
OK with me..... I admit readily to having only a fraction of the math
ability
that I would need to understand all of the things I know to be true...
..... Including Pi.............

Andy in Eureka, W4OAH, over-the-hill on Lake Richland-Chambers

) writes:
I have been looking into gizmos that improve CW copy. Most are audio
tone detectors that ignore short impulse noise bursts and then
regenerate the CW with a keyed tone oscillator. There are several of
these designs around and they are all well and good, but I stumbled
across something different and was wondering if any of you have had
personal experience with it?

An October 1971 article in Ham Radio magazine (pg 17) titled
"high-performance CW processor for communications receivers",
"Frequency modulating the telegraphy signals in your receiver provides
an interesting and profitable addition to conventional receiver
design".

I finally dug out the article. I haven't a clue to its worth, but
I don't recall that sort of scenario coming up in other places (while
the one about good filtering and using a detected voltage to key an
audio oscillator came up a number of times), which may mean nobody
found it useful, or nobody else could be bothered replicating the circuitry.
What you want to do is check a few issues later, to see if there were
any letters related to it in the "Comments" section.

It's interesting that the November 1971 issue of Ham Radio had an article
entitled "Weak Signal Reception in CW Receivers", which used nothing
cutting edge but was a summation of various things one could do to improve
reception.

Go back a few years, and you'd see an article or two about "under the noise"
CW reception, which of course amounted to PLLs driving some indicator, but
at the time were pretty out of the ordinary since IC phase locked loops
hadn't arrived.

I suspect to evaluate this, one really needs to dig through the magazines
and look at all the schemes. Ham Radio seemed to have a fair number in
the first decade or so. Something about that article you reference reminds
me of something in an article about a Hallicrafter's diversity receiver,
I forget the issue but it likely was in one of the annual October (or was
it November?) receiver issues. About '74 or '75, someone named Hilbert
had some scheme that involved active audio filters, but there was more
to it than I can think of at the moment. (I seem to recall there was
some "stereo" effect, in that different signals were fed to each ear,
which in itself may be worth pursuing. Use one of those schemes with
the detectors to key the audio oscillator, but also include some of
the signal from the receiver output, so you get the noise and the actual
signal in it.) Wait, I think it must have been "Hildreth", who also
wrote this article you reference. In which case, you can look up
what he did later; did he see some fault in this system, or did he
just realize it was easier to implement something at audio?

Someone mentioned in this thread something that hinted at Coherent
CW, which sync'd up the time and frequency at both ends to allow
for good filters and fairly deep in the noise CW reception. If you
know when and where to look, then it's easier to gather whether there's
a signal there or not.

By looking at the various schemes people have come up with, one
can get a better idea of each one's worth better than looking
at each one by itself.

Some of the schemes likely panned out to be duds. Others required
too much circuitry, at least at the time of the articles, so nobody
wanted to replicate them. And then likely they've been forgotten,
because otherwise more recent technology advances make the past easier
(look at how phasing SSB returned to some level of popularity when
ICs and digital audio came along). Others, like Coherent CW had
the disadvantage that they were a whole system, rather than a
processor, so you needed matching stations at both ends in order
for it all to work.

You can at least look over the cumulative index of Ham Radio magazine,
since someone has put it (or at least some version of it) online
at http://webhome.idirect.com/~griffith/hrindex.htm

Ham Radio seemed to be the place to look for that sort of out of
the ordinary schemes.

The idea is to sample the last IF of a receiver after as much IF
filtering as you can muster, and then using this as the RF input to a
FM modulator. The RF/IF is modulated at the audio frequency you like to
hear while copying CW. The next step is to frequency multiply the FM
modulated signal to increase the bandwidth and up the modulation index.
The following step is to treat it like any normal FM receiver IF and
run it through a limiter stripping off any amplitude information. The
last step is to put the signal into a normal FM discriminator to
recover the modulating tone you used.

What this is supposed to do is reduce or eliminate QRN (not QRM) from
the CW signal making a "quiet" background to copy the CW.

It gets the on/off of the keying, but yes it limits the signals. So
widely varying signals will be at about the same level (though that
may not always be a feature), and any QRN will be limited too.

In thinking about it, I'm not so sure it's all that distant from the
schemes that detect the CW and use that to key an audio oscillator. The
bulk of the circuitry is not there to improve the CW reception, but
to get that needed FM signal, with the incoming CW signal as
the "carrier".

Again, the more I think about it the more I think his later audio based
schemes may implement a similar concept.

Michael VE2BVW

"AndyS" wrote:

My ear copy can still pick those out, and many of the "processors"
can't deal with noisy sigs in that region. They tend to fall apart
when anything below tangential sensitivity is received.

Andy W4OAH in Eureka, Texas

Leif Asbrink, SM5BSZ, has some remarkable plots of moonbounce using
25W emitted from single 10 element yagi:

http://www.nitehawk.com/sm5bsz/kk7ka/kk7ka.htm

He gives his personal experience listening to weak Morse code he

http://www.nitehawk.com/sm5bsz/weakcom.htm

His entire site is packed with very useful information on receiving
weak signals, including his Linrad setup:

http://www.nitehawk.com/sm5bsz/weakcom.htm

Well worth exploring if you haven't had the chance.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automat...pler/intro.htm

About tone detection in noise with biaural hearing:
In an ancient magazine article (If I recall correctly it was "dubus") there
was a scientific reference mentioned. The signal must be delayed AND a
difference in power level feeding it to the ears. They mentioned it is
possible to get 3dB improvement with this methode.

Of course, detecting "submarine" is a good search for Google I think. They
do worn stereo head phones.

Signal detection in general is how the processing is done:
- online or offline. Offline gives the added benefit of knowing all the
signal in advance.
- bit-speed needed (Here the brain is bounded to limits)
- power level achievable (over background)
You can't beat the modern detection systems doing DSP algorithms.

- Henry

Mike Monett wrote:
"AndyS" wrote:

My ear copy can still pick those out, and many of the "processors"
can't deal with noisy sigs in that region. They tend to fall apart
when anything below tangential sensitivity is received.

Andy W4OAH in Eureka, Texas

Leif Asbrink, SM5BSZ, has some remarkable plots of moonbounce using
25W emitted from single 10 element yagi:

http://www.nitehawk.com/sm5bsz/kk7ka/kk7ka.htm

He gives his personal experience listening to weak Morse code he

http://www.nitehawk.com/sm5bsz/weakcom.htm

His entire site is packed with very useful information on receiving
weak signals, including his Linrad setup:

http://www.nitehawk.com/sm5bsz/weakcom.htm

Well worth exploring if you haven't had the chance.

Regards,

Mike Monett

Antiviral, Antibacterial Silver Solution:
http://silversol.freewebpage.org/index.htm
SPICE Analysis of Crystal Oscillators:
http://silversol.freewebpage.org/spice/xtal/clapp.htm
Noise-Rejecting Wideband Sampler:
http://www3.sympatico.ca/add.automat...pler/intro.htm



Andy comments:\

Mike,
The comments you have attributed to me in the above post
are in error. You mistakenly copied another's comments and
put my name in front of it....... Not a problem for me,but
I get into enough trouble on my own without having to catch
any hell for other people... (grin)

Andy W4OAH