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