Re: [Discuss-gnuradio] Radio Astronomy Spectrum Averaging interface; Osmosdr issue?

[Balthasar Indermuehle]

Hi Glen,

Looks like an interesting project! A couple of clarification questions:

Your aliased signal is the dark blue line that’s tracing the black and green lines except for (what you think is) the aliased HI signal at ~-75 km/s?

Have you double checked using known terrestrial emitters (or a satellite beacon if the antenna isn’t easily steered to horizon elevations) whether this isn’t simply a tuning issue? Also, when all else is solved, you may want to revert the X axis to increasing velocity left to right, and also double check you got your Vlsr calculations correct - the Perseus arm in common literature is thought to have HI and 12CO tracer velocities of -20 to -60 km/s (which would render your blue line the more credible one, of the x scale is indeed calculated correctly!)

I’ll take a look at your blocks later today.

Cheers

- Balthasar

On Tue, 8 May 2018 at 07:25, Glen I Langston <address@hidden> wrote:

Hello

A group of us working with Gnuradio to build home radio telescopes has been working for

a few years with gnu radio.   The code for our observations was in a form that was 

“orphaned” with changes to gnu radio. 

The observing interface has been re-released (in an improved form) via git hub.  It can

be obtained with

git clone http://www.github.com/glangsto/gr-nsf

Despite lots of work, the result is only a few new blocks in a python sub-directory

and .xml files in the “grc” sub-directory for use with with gnuradio-companion (GRC).   

The examples directory contains the .grc files to be run to make observations.

The examples README.md has instructions.

The examples directory also has two .grc files that test the blocks and

show now problems on either Ubuntu or Mac OS.

We find an issue for this code an Ubuntu, that is not present for Mac operations.

Using exactly the same code on Ubuntu shows the problem, while the mac code does not.

We guess the problem is in some way associated with our use of the Osmosdr block

and an AIRSPY mini.

The problem is that the spectrum has a weak alias relative to the center of the band pass.  

We’re hoping someone might have a suggestion on how to mitigate this problem on Ubuntu.

An example spectrum showing the interface and the problem is attached.

For Radio astronomy the galactic hydrogen signal is near 1420.4 MHz == 0 velocity.   The alias signal is “folded”

to the lower half of the band.  The green curve show the problem on Ubuntu.  The baby blue and red

signals were taken with the Mac and have no alias.  The hot load (red) was also taken with the Mac

Thanks in advance for any suggestions!

Regards

Glen

An Astronomically motivated figure is also shown 

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