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


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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.

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