Re: [Discuss-gnuradio] Questions

[David Brodrick]

Eric,

> The GUI stuff is generally pretty crufty right now.  Most of our
> effort of late has been in the ATSC receiver.  The GUI stuff will get
> an overhaul once that ATSC receiver is stable.

Perhaps we can ensure my work is complimentary to your plans.

My immediate interest is software correlators for radio interferometry.
I have written c++ implementations of this already but feel the useful
parts of the software should be integrated/reimplemented with a more
general library, so I was quite excited when google told me about
gnuradio!

I have built some simple interferometers using two direct conversion
receiver kits slaved to a common LO (20-30MHz). I presently use the
sound card for an ADC.

The software needs to do something like: perform a cross correlation of
the audio streams from the two receivers, average for some integration
period, take an FFT of the lag spectra to obtain the cross power
spectra, identify spectral channels of (dis)interest, and take vector
averages of the good channels. Down the track I may want quadrature
filters, phase rotation and other things. The process probably wants
time stamps and other header information passed around somehow.

If I enumerate some of my fledgling ideas for gnuradio integration
perhaps you could offer advice so that my work can fit with the
project's larger goals:

*Real cross correlator (guts implemented in MMX). Input: 2 time domain
signals. Output: 1 lag spectra. I see there are several correlating
modules already, but these do not seem sufficiently general to achieve
my goals.

*FFT module: input: numbers, output: FFT of input

*Maybe an Integrator, which takes lag or frequency domain input and
averages with some time constant.

*Maybe a Windowing class (if there isn't already) which applies a
tapered window to its input data. Perhaps this only needs to be internal
to the FFT module.

*AudioSource/AudioSink: I need to enable two audio input streams using
the stereo line-in channels (if requested at runtime) and implement a
AudioDevice base class for AudioSource and AudioSink so that the full
duplex cap of most devices can be exploited. This would be valuable for
most people without specialised conversion hardware (eg 99% of hams).

*I have been looking to reuse code from third party GPL QT libraries as
a versatile 2D/3D plotting class. This might end up as some kind of
general purpose base display class. What are your plans for the GUI?

*If I want to utilise existing libraries (eg for neural nets) how should
I manage that? Assume the system already has the library installed?

*I have frequency control of my DDS local oscillator. Does system
control have any place in gnuradio or should I keep such things at the
application level or in an alternate library such as hamlib?

Sorry for being a bit long, I want to get it right.

  Dave