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From: osr on 21 Mar 2010 11:16
NO issues with demodulation in a lab in the states if you do NOT
redistribute or discuss the demodulated content.

Since you do not have a target system in mind, at this time I would
strongly suggest a copy of the ARRL spread spectrum handbook, and
build some of the experiments in it, as most of the parts are still
available and some of the spread spectrum sources detectors can be
built for less then 50$.

IFs for most FH/DS radios are 70 to 200 Mhz. If you look at the
stats for the various IEEE 802.11 standards you can get a idea of
the bandwidths involved. A issue might be that modern radios might
have the IF contained on chip, you might need to find some older ebay
stuff, for example early Telxon data links, to find discrete IFs, or
chipsets that use external SAW filters.

If all your looking for is the carrier spikes, a spec an with a
minimum bandwidth of 10-20 kilohertz is probably just fine and you
probably could get away with 100 khz.

Steve

From: osr on 21 Mar 2010 11:18
here, This is outdated, but it is a good start

http://www.sss-mag.com/ss.html

You might want to see what you cna find on the old Harris PRISM
chipset

Steve

From: Tim Wescott on 21 Mar 2010 15:56
Tim Bently wrote:
> As part of a university course we are interested in monitoring and
> identifying FHSS signals within the commercial broadcast frequency
> spectrum. Please excuse a few questions.
>
> In technical terms, how does a spectrum analyzer lock onto a signal
> that constantly frequency hops?

It doesn't. Is that too technical?

> Can this still be achieved if the frequency divisions and timing are
> random?

It can't be achieved at all with a spectrum analyzer.

> What is the best type of spectrum analyzer for this purpose? Are any
> special options needed?

_If_ there is a plug-in or option for the spectrum analyzer that is
_specifically_ designed for the _specific_ spread spectrum service in
question then that would certainly make it possible. But then the
instrument would be a lot more than a "Spectrum Analyzer", and it's
operation would be explained in it's operating manual.

> Are there any technical guides available online that deal specifcally
> with this type of application?

Dunno -- you're asking a spectrum analyzer to be a very different
critter than it is now.

> Once again, sorry for the several questions. I don't know how else to
> ask.
>
> Thank you for any advice.

You need to build or find a receiver for the specific spread spectrum
service that you're trying to monitor. Then you need to decide what
'spectrum' you want to measure -- the spectrum as emitted from the
transmitter? The spectrum after despreading? What?

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
From: osr on 21 Mar 2010 16:17
For the record, in the near field, you can see a FH or DS signal, on
the spect an display. You just cant demodulate it, and only a crude
analysis can be performed. Which is what I suspect your instructor is
trying to teach you.

Steve
From: Tim Wescott on 21 Mar 2010 16:29
osr(a)uakron.edu wrote:
> For the record, in the near field, you can see a FH or DS signal, on
> the spect an display. You just cant demodulate it, and only a crude
> analysis can be performed. Which is what I suspect your instructor is
> trying to teach you.
>
> Steve

(Context please, this is a USENET newsgroup, even if you're using Google).

Possibly. A spread spectrum signal, properly done, could be secreted
inside the 'normal' FM band and wouldn't even show up above all the
'real' FM activity, yet would still show up just fine after being
correctly despread and demodulated.

You'd have no chance of seeing it with an antenna stuck onto the
analyzer -- you'd only be able to see it if you could tap straight off
the transmitter.

--
Tim Wescott
Control system and signal processing consulting
www.wescottdesign.com
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