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From: Tim Bently on 20 Mar 2010 21:11
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?

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

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

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

Once again, sorry for the several questions. I don't know how else to
ask.

Thank you for any advice.

Tim Bently
From: osr on 20 Mar 2010 22:18
Timing is derived from the spec an's own clock system. It does not
"cooperate" with the TX, unless you obtain one designed for radio
servicing that can demodulate a given application. Odds are for a
educational project at the undergraduate level you would not need a
demodulating capable unit. If you get access to a modern lab grade
one, will not drift any where near enough to cause you any issues. In
fact, for the most part, it will be more stable the then spread
spectrum transmitter is. You need to give us more data as to the
frequency band and radio service you wish to look at, as with what you
have said we could specify anything from a modified TV tuner hooked
to a ramp generator and oscilloscope to a 40,000$ instrument.. You
might wish to get on interlibrary loan a copy of the ARRL Spread
Spectrum Handbook, which is outdated but very useful from a beginning
point of view.

I'm assuming you mean at 88-108 Mhz FM, or are your looking at
Digital Radio Mondial ? Or the UK/EU service at 200-300 Mhz?

Without knowing the target application, It is impossible to suggest a
unit without knowing frequency band, desired bandwidth, and noise
floor/sensitivity issues for the instrument.


Start with this:

http://www.home.agilent.com/agilent/redirector.jspx?action=ref&cname=AGILENT_EDITORIAL&ckey=459602&lc=eng&cc=US&nfr=-536902453.0.00

And This:

http://www.tek.com/Measurement/App_Notes/XYZs/

And look at home made systems here:

http://www.qsl.net/n9zia/wireless/pdf/9808035.pdf

and here:

http://homepages.wmich.edu/~cotton/SA1.html

and here:

http://www.scottyspectrumanalyzer.com/

I'm not sending you to the home-made systems to suggest you build one,
I'm sending you there to learn how a simple single stage
superheterodyne SA works...

Steve







From: mpm on 20 Mar 2010 23:35
On Mar 20, 9:18 pm, o...(a)uakron.edu wrote:
> Timing is derived from the spec an's own clock system.  It does not
> "cooperate" with the TX, unless you obtain one designed for radio
> servicing that can demodulate a given application.  Odds are for a
> educational project at the undergraduate level you would not need a
> demodulating capable unit.   If you get access to a modern lab grade
> one, will not drift any where near enough to cause you any issues. In
> fact, for the most part, it will be more stable the then spread
> spectrum transmitter is.  You need to give us more data as to the
> frequency band and radio service you wish to look at, as with what you
> have said we could specify anything from a  modified TV tuner hooked
> to a ramp generator and oscilloscope to a 40,000$ instrument..   You
> might wish to get on interlibrary loan a copy of the ARRL Spread
> Spectrum Handbook, which is outdated but very useful from a beginning
> point of view.
>
> I'm assuming you mean at  88-108 Mhz FM, or are your looking at
> Digital Radio Mondial ?  Or the UK/EU service at 200-300 Mhz?
>
> Without knowing the target application, It is impossible to suggest a
> unit without knowing frequency band, desired bandwidth, and noise
> floor/sensitivity issues for the instrument.
>
> Start with this:
>
> http://www.home.agilent.com/agilent/redirector.jspx?action=ref&cname=....
>
> And This:
>
> http://www.tek.com/Measurement/App_Notes/XYZs/
>
> And look at home made systems here:
>
> http://www.qsl.net/n9zia/wireless/pdf/9808035.pdf
>
> and here:
>
> http://homepages.wmich.edu/~cotton/SA1.html
>
> and here:
>
> http://www.scottyspectrumanalyzer.com/
>
> I'm not sending you to the home-made systems to suggest you build one,
> I'm sending you there to learn how a simple single stage
> superheterodyne SA works...
>
> Steve

I'm not aware of any FHSS in the Commerical Broadcast Band (US: 88-108
MHz) ?
Except possibly for very low power Part-15 emissions.
-mpm
From: Tim Bently on 21 Mar 2010 00:25
On Sat, 20 Mar 2010 19:18:13 -0700 (PDT), osr(a)uakron.edu wrote:

>Without knowing the target application, It is impossible to suggest a
>unit without knowing frequency band, desired bandwidth, and noise
>floor/sensitivity issues for the instrument.
>

Thank you for your informative reply. There is no particular band of
interest, as such.

The idea was simply to "sniff" around the radio and IF broadcast bands
and demonstrate objectively how it is utilized by FHSS.

IOW to find FHSS "hidden" information content and folllow it as it
shifts from carrier to carrier, noting the spread, time intervals,
etc.

If the modulating signal could also be demodulated/isolated, that
would be a plus. Now that I think of it, I am wondering to what extent
this is actually possible given privacy issues with telecoms.

Of course, it would be desirable to demonstrate this over as wide a
bandwidth as possible, but without making the exercise inordinately
difficult.

Any further suggestions along these lines would be much appreciated.

Tim Bently
From: Mark on 21 Mar 2010 09:13
On Mar 21, 12:25 am, timben...(a)peromax.com (Tim Bently) wrote:
> On Sat, 20 Mar 2010 19:18:13 -0700 (PDT), o...(a)uakron.edu wrote:
> >Without knowing the target application, It is impossible to suggest a
> >unit without knowing frequency band, desired bandwidth, and noise
> >floor/sensitivity issues for the instrument.
>
> Thank you for your informative reply. There is no particular band of
> interest, as such.
>
> The idea was simply to "sniff" around the radio and IF broadcast bands
> and demonstrate objectively how it is utilized by FHSS.
>
> IOW to find FHSS "hidden" information content and folllow it as it
> shifts from carrier to carrier, noting the spread, time intervals,
> etc.
>
> If the modulating signal could also be demodulated/isolated, that
> would be a plus. Now that I think of it, I am wondering to what extent
> this is actually possible given privacy issues with telecoms.
>
> Of course, it would be desirable to demonstrate this over as wide a
> bandwidth as possible, but without making the exercise inordinately
> difficult.
>
> Any further suggestions along these lines would be much appreciated.
>
> Tim Bently

without knowledge of the hopping, it is very difficult for a standard
swept spectrum analyzer to follow a FHSS signal, finding this out
first hand may be the point of the exercise that you were assigned.

There are analyzers called "real time spectrum analyzers" that
basically record a range of frequencies and can analyze them after the
fact. With one of these you can start to analyze an unknown FHSS
signal.

Mark
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