RE: [Discuss-gnuradio] gnuradio based spectrum analyzer

[John Ackermann N8UR]

OK -- I need to explain a bit more what I'm up to.  There's a ham radio 
operating event where a station (W1AW, the headquarters station of the US 
amateur radio organization) transmits a series of 60 second carriers on 
several frequency bands.  The challenge is to measure those signals with as 
much accuracy as possible.  The signal is not incredibly strong, and it's 
subject to the vagaries of propagation and interference from other sources 
(and things like power line noise, etc.).  My technique is to tune in the 
unknown signal and inject a known reference frequency a few tens of Hz 
away, and then measure the delta between the two in the audio passband -- 
this way any drift in the receiver is common mode and affects the two 
signals equally.

Last year I used the baudline spectrum analyzer software and it worked 
pretty well, but the maximum FFT size is 32768 which led to a couple of 
limitations.  I had to slow down the sample rate to 400/second to get a 0 
to 200Hz displayed bandwidth, which yielded a resolution of (I think) 
0.16Hz but required me to tune the notes to an awfully low frequency, which 
presents a few problems with the receiver interface.

For this year, I'm hoping to come up with something that will give me even 
better resolution but let me put the signals at a bit higher audio 
frequency for the measurement.

The waterfall display does a good job of letting you find the main signal 
against the noise, and also lets you track the propagation variations and 
pick the best spot in the history to do the measurement.

Hope this clarifies things.

John

--On Thursday, September 25, 2003 18:38:30 -0400 "Deary, Bryce D. (BDEARY)" 
<address@hidden> wrote:

> If you already have a reference, why not just mix the reference with the
> measured signal, low pass filter to 100Hz and run it into a counter?
>
> -----Original Message-----
> From: John R. Ackermann N8UR [mailto:address@hidden
> Sent: Thursday, September 25, 2003 2:20 PM
> To: address@hidden
> Subject: [Discuss-gnuradio] gnuradio based spectrum analyzer
>
>
> Hi --
>
> This is both a query for information, and a bit of begging for help.
>
> I want to put together a sound-card driven audio spectrum analyzer for a
> very specific purpose (measuring the frequency delta between two closely
> spaced RF carriers that have been brought down to audio via a receiver).
> I  would like to get resolution in the range of 0.01Hz over about a 100Hz
> display window centered at 800Hz or so (the precise center frequency
> isn't  a big issue).  I'd like a basic waterfall display and the ability
> to  measure the frequency delta between two points on the display.  I
> need to  display the data in near real time for tuning purposes, though I
> don't need  the full resolution in real time -- as long as I can capture
> the data  stream for later analysis with the deep FFT, 1Hz resolution in
> near real  time is good enough.  I don't need any other fancy features at
> all.
>
> My question is first, would gnuradio be a good candidate to do this?
>
> Second, as I've yet to actually *use* gnuradio for anything, would some
> kind soul here be willing to help me with development?  I need to have
> this  working by mid-November, and I'm starting from absolute ground zero
> in DSP  programming (and graphics programming, too).
>
> Thanks to anyone brave enough to help me out :-)
>
> John N8UR
> address@hidden
>
>
>
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