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