First-time radio astronomer, looking for advice

[Robert Hamers]

I'm a total newbie at radio astronomy but have been doing astrophotography for years and have a strong background in electronics and some prior experience in radio and programming. I built a modest-size rectangular horn (~ 1 m x 0.8 m top dimension) and am using the Nooelec H1 Sawbird, Airspy R2, and a headless Raspberry Pi 5 (which I connect to via TigerVNC).   For software I'm using the gnuradio-companion, DSIPRA software (spectrometer_w_cal.grc) with the gr-osmocom radio block. I've gotten some decent first results (below) looking at the MW cutting through the south meridian, AM and PM.  (spectra are 2-minute averages) I'm pretty pleased with this as initial results, but have some issues and looking for help. 

1) I'm getting a lot of "spikes" noise in the spectra, which you can see below. The individual frequencies seem to be quite reproducible but intensities vary. I'm not sure if this is an issue in the electronics or what to do to get rid of it.  

2) Using the Gnuradio-companion and gr-osmocom radio block,  setting the RF, IF, and BB gain seems to be very irreproducible...sometimes it seems the gain "takes" and sometimes it doesn't.   I'm wondering if there is better/different software out there compatible with the Airspy R2 , ideally compatible with RPI/Raspbian, but generally open to all kinds of suggestions. 

 

[fasleitung3]

Hi Robert,

You are getting pretty good results, congratulations.

Your spikes in the spectrum are most likely caused by some interfering device in the vicinity. A typical offender are monitors. You could try relocating the monitor or if possible turn it off when taking data to try that. If that is not the cause, than look at other devices you have around, including the Pi. Keeping digital electronics away from the antenna as far as possible is a good thing to do.

As far as I know, spectrometer_w_cal.grc is an older version. You could try their newer version gr-radio_astro, https://github.com/WVURAIL/gr-radio_astro. Maybe that cures your problem.

Other than that, you may want to look at some other software which supports the Airspy and will most likely run on a Pi 5:

Virgo: https://github.com/0xCoto/Virgo

RadioPy: https://github.com/byggemandboesen/RadioPy

Spectro_radiometer https://github.com/ccera-astro/spectro_radiometer

You may also want to check whether the parameters for the gain you are using are all in the permissible range. I could imagine that if that is not the case, the setting may just be ignored.

Best regarsd,

Wolfgang

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[Robert Hamers]

Thank you, Wolfgang- this is all quite helpful !

best wishes,

Bob Hamers

[Alex P]

Hello Robert,

Here is info on software easy to use and from which you can obtain good results ..

( It does require MS Win 7,10,11 )

The processing sequence is  AirSpy SDR# > IFavg > HLine3D > Rinearn (graphics )

https://github.com/AP-HLine-3D/HLine3D

Regards,

Alex Pettit

[b alex pettit jr]

The processing sequence is  AirSpy SDR# > IFavg > HLine3D > Rinearn (graphics )

https://github.com/AP-HLine-3D/HLine3D

Regards,

Alex Pettit

[Ayushman Tripathi]

Hi Robert,

I'm also running a fully remote & automated system using a Raspberry Pi 500. I wrote a script, later converted to a systemd service, which runs continuous observation loops, each loop is 24 hours of 5-minute integrations. It uses VIRGO software and an Airspy SDR. The system automatically records both raw and calibrated data on the Pi.

On my main PC, a second script handles everything else, reprocessing with VIRGO, baseline correction, and plotting. It supports multiple plot types, including 3D VLSR-corrected stacked plots, etc.

The whole pipeline is largely automatic once running. It's not perfect and it has bugs for sure, which is why I haven't published it on GitHub. But if you're interested, I'm happy to share both scripts on GitHub public repo.

The attached plots are from this same pipeline.

Thanks

[Robert Hamers]

Thanks for the helpful comments !  I've tried the IFAvg plug-in for SDR# and that is definitely an improvement over what I was using previously.  I"m still open to any additional suggesions and would like to try the software from Ayushman as well. 

[b alex pettit jr]

Robert, 

If you have SDR# & IFavg installed and can save *.txt files, HL3D is a near trivial operation to remove offset drift and

calibrate the HLine data files in dB normalized to Cold Sky. There are stepbystep instructions for using Rinearn to create some nice plota.

HL3D

Find the Data Files load & click Ok

Hit  PROCESS.

The results are written into  data subdirectory 

Load them into either Excel or Rinearn for plotting

( Rinearn 2D )

Raw Data

Drift  ( Sun drifted into side lobe of antenna @ ~19-23 hrs  )

Corrected, Normalized,  dB Scaled Data 2D

above data w/ Rinearn 3D

Alex Pettit

GitHub - AP-HLine-3D/HLine3D: Beginners Low Cost 21cm Radio Telescope Project b.alex.pettit.jr.

GitHub - AP-HLine-3D/HLine3D: Beginners Low Cost 21cm Radio Telescope Pr... Beginners Low Cost 21cm Radio Telescope Project b.alex.pettit.jr. - AP-HLine-3D/HLine3D

[b alex pettit jr]

Another plug for  SDR# > IFavg > HL3D : The data is Calibrated and Scaled in engineering units.

Meaning :  You can compare changes in your hardware setup and compare the performance of your system against others.

I have data sets from the US & Europe on systems from simple 1m antennas to a 

          12m radio telescope in Neu Golm, Germany.

Alex Pettit

========================================

On Wednesday, March 4, 2026 at 01:17:57 PM EST, Robert Hamers <rjha...@gmail.com> wrote:

[b alex pettit jr]

Robert, 

If you have or can record a set of IFavg data files, send them to me.

I'll Process them via HL3D & Plot w/ Rinearn .

Alex

On Wednesday, March 4, 2026 at 01:17:57 PM EST, Robert Hamers <rjha...@gmail.com> wrote:

[Robert Hamers]

Hi-

Thanks for the offer! I have rather limited visibility from my home so I”ve been just doing short spectra (~ 2 min) as the MW crosses the south meridian and different elevations in the evening and then again in the morning.  So not enough to make a 2D map.  There is another location I can move to that will give me broader visibility but I want to have everything else optimized before doing that.  But that’s my goal!  

So far the IFAvg plugin is working well.  It sometimes crashes inexplicably when I choose 1024 or 2048 FFT length,  but if it doesn’t crash immediately it seems to be stable afterwards… I’ll probably try another set of meridian-crossing data files later this evening and tomorrow, weather permitting…

Thanks again for your help and offer!

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[b alex pettit jr]

" Thanks for the offer! I have rather limited visibility from my home so I”ve been just doing short spectra (~ 2 min) as the MW crosses the south meridian and different elevations "

That's how a drift scan it done : Set the dish pointed along your Meridian at some Elevation & Let the Sky Drift By .. for 24 hrs or so

Earth's Rotation provides the RA axis ..

I typically acquire 5 min samples w/ 512 FFT freqs.

Watch this perhaps ?

Alex Pettit: Galactic Hydrogen 1.42 GHz RF Emission Radio Astronomy for $300

Alex Pettit: Galactic Hydrogen 1.42 GHz RF Emission Radio Astronomy for ...

Alex

[b alex pettit jr]

This is a good chart to use for finding bright areas of the MW H Line

( Dec+20 & Dec+40 are the best if you can see them with your antenna )

Set up your system for 2min or 4min samples & let it run for 24 hrs ..   Send me the 360 or 720 set of spectra

( A pre-test IFavg background correction will remove the gain vs freq curve of the LNA/SDR )

Alex

[Ayushman Tripathi]

Hi Robert,

I uploaded both scripts to GitHub https://github.com/ayushman-t/h-line-observer I'd suggest trying h_quick first to make sure everything works before going automated.

I cleaned up the paths and settings that were specific to my Pi and made them a bit more flexible, there may still be some bugs.

h_quick.py — a simple manual testing tool. Just run it, pick a calibration from the menu (or record a new one), then choose single observation or continuous loop. Good for checking everything works before going fully automated. Both scripts will also generate 5-minute plots using the default VIRGO output which should be fine for a quick test.

h_observer.py — the main automated script. Run it once with --install to set up, then --config to pick your SDR and output folder, record a calibration pointing at cold sky, and then start the systemd service. From that point it runs 24/7 on its own, creates a new folder each day and resumes automatically after a power cut.

I'll upload the pipeline script that handles the combined plotting and analysis of the full 24-hour loops soon.

If you face any issues, I'll be happy to help.

Thanks

[Robert Hamers]

Thanks!

Are there any prerequisites beyond ones I might already have (e.g.,  python 3.9,  numpy,  astropy ) ?

bob

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[Ayushman Tripathi]

Hi Robert,

For the prerequisites, just GNU Radio and VIRGO. 

Installing VIRGO automatically includes numpy, matplotlib and astropy, so no additional packages needed beyond what you already have.

For installation: https://virgo.readthedocs.io/en/latest/installation.html

Thanks​.

Sent from my iPhone

On 5 Mar 2026, at 20:04, Robert Hamers <rjha...@gmail.com> wrote:



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