First Drift Scan from my 2.4m Dish with Airspy Mini and VIRGO

[Ayushman Tripathi]

Hi!

Here's the H-line data I captured from my 2.4m dish station in a 21-hour drift scan. I've attached an interactive 3D HTML plot you can rotate, zoom, and hover to see RA, Dec, frequency, and Doppler velocity for each point, along with plot images.

You can see the RA progression in the plot corresponding to each hydrogen peak as the Milky Way drifted through the beam.

There's little to no RFI in the raw data now. I'll do longer observations soon and share the results.

I'll optimize the data processing and plotting in the coming days.

System details:

• Hardware: Airspy Mini

• Software: VIRGO-based script

• Feed: Cantenna with SAWbird H1 LNA

• System: Raspberry Pi 500, fully remote operation

•   Dish: Fixed pointing for now

3D HTML URL:   https://www.icloud.com/iclouddrive/078xlIb4HBU2AQ_MYqDiosd3Q#hline%5F3d%5Finteractive



Thanks

[Alex P]

Hello Ayushman,

Good Work !

Can you acquire a 24 hr slice at either Dec +20 dg or Dec +40 dg ?

These are some of the brightest regions of the MW.

Thanks,

Alex

[Ayushman Tripathi]

Hi Alex,

Thank you! Yes, I'll do 24/7 drift scans since the dish is fixed pointing and I'm obtaining the data remotely. I can visit once every ~2 months to adjust the pointing. The good thing is there's not even a single RFI spike visible in the raw data as I turned off even any light bulbs. 

I'll also create a Zenodo page so the data is properly archived and verifiable if I find anything unusual.

Thanks.

[b alex pettit jr]

Ayushman,

Why are you taking 24/7 scans of the same region ?

What changes from day to day ?

Do you have a better plot of this.

There seems to be an unusual pattern in the background .

Alex

[Ayushman Tripathi]

Hi Alex,

Stacking multiple days should improve SNR, and it also helps with transient detection since any unusual signals would stand out. Real astronomical signals should repeat, while RFI won’t.

I visit the site every 2 months, so I’ll change the pointing to a different declination on my next visit. My long-term goal is to set up 3-4 dishes of 2m or larger for SETI observations. A motorized remote control mount would be nice, but for a dish this size I’d need to build one myself. By the way I think for smaller dishes like DD and WiFi dish Discovery Drive motorized mount should be available soon as per the discovery dish web page,

Regarding the better plot, yes, I captured the data but haven’t processed it yet. I’ll process yesterday’s data soon and share. Did you get a chance to look at the 3D HTML plot?

Thanks.

On 11 Feb 2026, at 06:27, 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



Ayushman,

Why are you taking 24/7 scans of the same region ?

What changes from day to day ?

Do you have a better plot of this.

There seems to be an unusual pattern in the background .

<1770771252570blob.jpg>

Alex

On Tuesday, February 10, 2026 at 07:16:52 PM EST, Ayushman Tripathi <ayushmantr...@gmail.com> wrote:

Hi Alex,

Thank you! Yes, I'll do 24/7 drift scans since the dish is fixed pointing and I'm obtaining the data remotely. I can visit once every ~2 months to adjust the pointing. The good thing is there's not even a single RFI spike visible in the raw data as I turned off even any light bulbs. 

I'll also create a Zenodo page so the data is properly archived and verifiable if I find anything unusual.

Thanks.

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[Ayushman Tripathi]

Also, could you please point out which part you’re referring to ? 

And It might be a data processing artifact, I’ll be improving the processing soon.

Here’s the link of discovery drive: https://www.rtl-sdr.com/discovery-drive-an-affordable-antenna-rotator-crowd-funding-pre-launch-page-now-active/comment-page-1/

[Stephen Arbogast]

Congratulations  Ayushman, I  can tell  you are  are  excited. The  journey is just  beginning.

I  too  am waiting  for the Kraken RF   motor drive  for  my  discovery dish.

I am just  wondering   if  multiple  measurements  separated by days  would  be helpful since our  earth moves around the sun or  maybe  the differences would  be  insignificant...     any thoughts?

Stephen

[b alex pettit jr]

Hi Ayushman,

I looked at the 3D plot, but at that angle, it is difficult to eval the actual data ..

That is why I prefer the Z axis orientation.

" Also, could you please point out which part you’re referring to ? "

THIS

'Stacking' multiple days/weeks of signals will require LSR correction. Is that enabled in your software ?

Alex

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

On Tuesday, February 10, 2026 at 09:59:04 PM EST, Ayushman Tripathi <ayushmantr...@gmail.com> wrote:

Hi Alex,

Stacking multiple days should improve SNR, and it also helps with transient detection since any unusual signals would stand out. Real astronomical signals should repeat, while RFI won’t.

[fasleitung3]

As the earth moves around the sun and as a smaller contribution the earth rotates, there is a doppler shift which varies over time. The variation over just a few days may be not too significant but if you are talking about longer time frames this becomes important.

The solution to this is to correct all measurements for this and relate velocities to the local standard of rest. I highly recommend to do this in any case.

I wrote an article about this in the July/August 2021 issue of the SARA journal. For your convenience, I have attached this article here.

Best regards,

Wolfgang

[b alex pettit jr]

Thanks Wolfgang.

 this is a link to a VLSR Calculator 

http://f4klo.ampr.org/vlsrKLO.php

Alex

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

[b alex pettit jr]

This gives an idea of the VLSR error / day 

The VLSR curve shifts with respect to the MW as the Earth rotates about the Sun 

                Alex  P

[Ayushman Tripathi]

Hi Stephen,

Thanks! Yes, it'll help a lot for DD and WiFi dishes, as we can remotely control them then.

[Ayushman Tripathi]

Hi Alex,

Yes, that background jump in that RA slice, was not in yesterday's data, but it was in the 9th Feb data.  It might be something specific to that observation.
I'll try to find the reason why it appeared in that plot but not in yesterday's. I'll also reprocess the 9th Feb data to make sure something didn't get messed up in the script.

Yes, VIRGO supports VLSR, there's a vlsr=True parameter in the plot function that displays the graph in the VLSR frame of reference. I tried it last month and will try it again soon.
I've attached yesterday's plots and also the 3D HTML that you can rotate and check.


3D LIVE HTML: https://www.icloud.com/iclouddrive/0f4xYAqp0Xkwf6xu4eDn7l2MQ#hline%5F3d%5Finteractive_2

[b alex pettit jr]

Hi Ayushman,

What causes this  pattern in the plots ?

If you want to find low level signals, these could be a problem

[Ayushman Tripathi]

Hi Alex,

Those appear to be 3D rendering artifacts from matplotlib's 3D rendering. I'm working on fixing that.

Interestingly, when I plot the same data using Plotly (WebGL-based), those tiny squares don't appear.

Thanks.

You can find the whole 3D Plot attached here:  https://www.icloud.com/iclouddrive/0f4xYAqp0Xkwf6xu4eDn7l2MQ#hline%5F3d%5Finteractive_2

[b alex pettit jr]

Hi Ayushman,

This Looks Good !!!

Make sure any AGC option on the SDR is Disabled ( automatic gain control )

The dark region ( shown in box ) looks like a decreased gain due to the H signal  .. maybe ?

[Peet Denny]

Awesome stuff, Ayushman. Very beautiful.

What explains the sinusoidal distribution of *frequency* in this plot?

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[Alex P]

On Thursday, February 12, 2026 at 10:15:10 AM UTC-5 Peet Denny wrote:Awesome stuff, Ayushman. Very beautiful.

[Ayushman Tripathi]

Hi Alex,

Yes, looks like it. I'll make sure the AGC stays off, it should be off already, but I'll double-check.

Thanks.

[Ayushman Tripathi]

Hi Peet,

Thank You. Yes, as Alex mentioned, the plot is still in the topocentric frame. I’ll apply the VLSR correction and compare the result.

On Thursday, February 12, 2026 at 10:15:10 AM UTC-5 Peet Denny wrote:

[Stephen Arbogast]

Wolfgang,

Thank you for  your  article.  

[Ayushman Tripathi]

Hi Alex,

The artifact that appeared similar to automatic gain control (AGC) effect from the SDR was actually caused by the baseline correction. I’ve corrected it and will share a few days of VLSR-corrected averaged data soon.

I’ll also upload the data to GitHub weekly.

Also next month I’ll move my DD feed to the same remote location where the 2.4 m dish is installed, and use a 1.5 m solid dish instead of the WiFi dish as that place doesn't have RFI problem.

Thanks

[b alex pettit jr]

Hi Ayushman,

My correction technique is not always Perfect either  :)

Regards,

Alex

[Ayushman Tripathi]

Hi,

This is 96 hours of hydrogen line data from my 2.4 m dish. I applied VLSR correction and then stacked the data by averaging observations at matching sky positions.

I’ve also attached an interactive 3D plot of the VLSR-corrected stack, which you can rotate and explore.

A plot below is the continuous observation without VLSR correction.

This is an initial version, and I will try to improve it further.

3D interactive plot: https://www.icloud.com/iclouddrive/0bdHs69Kk3-MVOrhd-6YUm8Ww#hline%5Fstacked

Thanks.

[b alex pettit jr]

Hello Ayushman,

That is excellent data ...  You are now achieving HLine plots of high quality.

Congrats :)

Alex

[Ayushman Tripathi]

Hi Alex,

Thank you. I’ll share the whole week's data by the weekend.

I’m currently working on a mechanism to remotely control the azimuth of the dish as well.

[b alex pettit jr]

Hello Ayushman,

Typically, for Drift Scans, the dish is always aligned N-S in Azimuth but adjusted in Elevation .

Can you change Elevation to get a sky slice @ Dec +20 Degrees ?

Alex

[Ayushman Tripathi]

Hi Alex,

Sure, I'll do that once I visit the site next.

Thanks.

Sent from my iPhone

On 20 Feb 2026, at 07:37, 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



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[b alex pettit jr]

Hello Ayushman,

Here is a plot from my 1.2m dish @ Dec + 20 Degrees

                                         VLSR Corrected     Y axis : +- 100 Km/Sec

Alex

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

On Thursday, February 19, 2026 at 10:30:38 PM EST, Ayushman Tripathi <ayushmantr...@gmail.com> wrote:

Hi Alex,

Sure, I'll do that once I visit the site next.

Thanks.

[Ayushman Tripathi]

Hi,

Attached is the last half of February data from my 2.4m dish. I've included both the VLSR-corrected stacked plot and a 12-day drift scan showing the full observation period.

I noticed an apparent frequency offset in the Feb 26 data, likely an LO drift, I will investigate this further.

I will visit the site later this month to adjust the dish pointing.

I've also uploaded the raw data to Zenodo, you can access it here: https://zenodo.org/records/18847536

Thanks

[b alex pettit jr]

              VERY IMPRESSIVE !!

You have consistent, clean RFI free data, and your VLSR correction is functioning well.

Congrats,

Alex P

[Ayushman Tripathi]

Hi Alex, Thank You.

Sent from my iPhone

On 3 Mar 2026, at 16:41, 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:



              VERY IMPRESSIVE !!

You have consistent, clean RFI free data, and your VLSR correction is functioning well.

Congrats,

Alex P

<1772536146062blob.jpg>

On Tuesday, March 3, 2026 at 05:55:28 AM EST, Ayushman Tripathi <ayushmantr...@gmail.com> wrote:

Hi,

Attached is the last half of February data from my 2.4m dish. I've included both the VLSR-corrected stacked plot and a 12-day drift scan showing the full observation period.

I noticed an apparent frequency offset in the Feb 26 data, likely an LO drift, I will investigate this further.

I will visit the site later this month to adjust the dish pointing.

I've also uploaded the raw data to Zenodo, you can access it here: https://zenodo.org/records/18847536

Thanks

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[Ayushman Tripathi]

  Hi Alex,
                                                                                                                                                                                       
  I'll be travelling to my 2.4m dish site tomorrow and will adjust the pointing, I'll change the elevation to get a sky slice at DEC +20° as you suggested. I'll share my last month's
  observation plots later this week.                                                                                                                                                    

  Thanks

[b alex pettit jr]

Hi Ayushman,

If +40deg Dec is visible from your location, it contains much more detail.

- Alex

[Ayushman Tripathi]

Hi, Alex. 

Thanks, I’ve now pointed the dish toward +40 dec, and I’m getting good results. I’ll share the latest observations with that DEC tomorrow. For now, I’ve attached some results from my March observations.

[Ayushman Tripathi]

Hi Alex,

Here's the data from the new pointing at DEC +40.

Thanks.

[Ayushman Tripathi]

Also, this is a Plotly HTML 3D plot at DEC +40

https://www.icloud.com/iclouddrive/01aWfgbDrS8F__iY7BNG3k8kA#april5%5F6%5F7%5Fstacked

[b alex pettit jr]

High Resolution Hline Details over a Very Flat Noise Floor . Excellent !

   What is causing the sharp steps in the peaks ?  

Thanks,

Alex

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

On Wednesday, April 8, 2026 at 02:37:55 PM EDT, Ayushman Tripathi <ayushmantr...@gmail.com> wrote:

Also, this is a Plotly HTML 3D plot at DEC +40

https://www.icloud.com/iclouddrive/01aWfgbDrS8F__iY7BNG3k8kA#april5%5F6%5F7%5Fstacked

On Monday, April 6, 2026 at 4:08:43 PM UTC-4 Ayushman Tripathi wrote:

Hi Alex,

Here's the data from the new pointing at DEC +40.

Thanks.

[Ayushman Tripathi]

Hi Alex,

It's most likely caused by the 5-minute observation interval, where the signal jumps a bit between consecutive observations as sources drift through the beam. The median filter VIRGO applies during processing also contributes a bit on top of that. I'm still investigating to see if there's anything else.

Thanks. 

[Ayushman Tripathi]

Also, here's the VLSR-corrected stacked 3D plot at DEC +40 DEG, interactive Plotly HTML. Thanks

https://www.icloud.com/iclouddrive/03fXnGanCGt5Lt_VVo7vt5yVQ#april5%5F6%5F7%5Fstacked%5Fvlsr

[b alex pettit jr]

From my 1.2m system

On Thursday, April 9, 2026 at 10:14:21 AM EDT, Ayushman Tripathi <ayushmantr...@gmail.com> wrote:

Hi Alex,

It's most likely caused by the 5-minute observation interval, where the signal jumps a bit between consecutive observations as sources drift through the beam. The median filter VIRGO applies during processing also contributes a bit on top of that. I'm still investigating to see if there's anything else.

Thanks. 

On Wednesday, April 8, 2026 at 2:48:18 PM UTC-4 b alex pettit jr wrote:

High Resolution Hline Details over a Very Flat Noise Floor . Excellent !

   What is causing the sharp steps in the peaks ?  

Thanks,

Alex

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

[Ayushman Tripathi]

Hi, Alex

Nice!

Yes, it looks similar in structure.

Thanks.

[b alex pettit jr]

Hello Ayushman,

What does your data look like from a full  Z axis ? 

Alex

[Ayushman Tripathi]

Hi, Alex

Here's the same data from the Z-axis view.

Thanks.

[b alex pettit jr]

Hi Ayushman,

I wonder if those 'vertical' sample-to-sample variations are associated with your implementation of Median Filtering ?

[Ayushman Tripathi]

Hi Alex,

It seems to be a mix of the observation-to-observation gain variation and some contribution from the median filter during processing. The variation seems to scale with signal strength. I am still investigating the issue and working on ways to improve it.

Thanks

[b alex pettit jr]

Here's an idea : Turn OFF any 'signal processing' that filters or modifies the data and record just the received signals for 6 (?) hours and plot ..

 that should help determine if it is an issue with the actual Received Signal or Processing ... it is Not 'real'.

[b alex pettit jr]

Do you employ any " Cold Sky Normalization "

I typically acquire 24 hr sessions

pick a freq that is beyond any H influence

scan through the data set a that freq ( +- 5 FFT bins ) and save each value.  ( and plot the results )

find the lowest and ( in the Power domain ) subtract from every other frame what is required to shift their value to that

( not same data set as above )

Raw Data Set                          Frame to Frame Drift @ selected Cold Sky Freq       Resultant CSN normalized Data

I then calculate a linear mX+b correction between the user specified CSN Low &  CSN high freq values and shift data accordingly

Alex

[b alex pettit jr]

Matlab Processing  ( Cold Sky Normalization ) &  Astronomy Art     @ 1:22 - 1:42 Hrs into presentation

RTOP Oct 2023: Masers, Interferometry and Hydrogen Observation Art

RTOP Oct 2023: Masers, Interferometry and Hydrogen Observation Art

[Ayushman Tripathi]

Hi Alex,

Thanks! I'll check that presentation.

The issue was with the baseline correction, which handled the two sides of the band asymmetrically and caused the artifacts. I've fixed it, and the plots are much cleaner now. Here's the updated version with the issue partially fixed.

And yes, I use cold sky calibration, a reference observation pointing away from the galactic plane, this option is present by default in Virgo.

I'll improve the baseline correction further this weekend and share the results.

[Mathew George]

Been trying to setup Virgo in UBuntu 24, but got stuck on virtual environment (for Virgo) and normal environment for GNU-Radio. Anyone who could advise how to work around this issue?

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___________________________

Mathew George, Ph.D.
Assistant Professor of Physics
Sacred Heart College (Autonomous), Thevara 

Kochi, India, 682 013
Mail: mathew...@shcollege.ac.in |
Web: https://mathewgeorge.shcollege.ac.in/ | https://matgeor.github.io/

[Ayushman Tripathi]

Hi Alex,

I improved the plotting a bit but ended up with some new artifacts while fixing the older ones :) I'll try fixing these later this week to get a cleaner baseline. Going to think of some new approaches.

Here are the improved ones I managed to get today.

Thanks.

[b alex pettit jr]

Hello Ayushman,

Looks Great .. I still get strange 'frames'  now and then also that I've never understood.

If it was Too Easy, this Hobby would be Boring 

Thanks,

Alex

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

On Sunday, April 12, 2026 at 07:02:35 PM EDT, Ayushman Tripathi <ayushmantr...@gmail.com> wrote:

Hi Alex,

I improved the plotting a bit but ended up with some new artifacts while fixing the older ones :) I'll try fixing these later this week to get a cleaner baseline. Going to think of some new approaches.

Here are the improved ones I managed to get today.

Thanks.

[Ayushman Tripathi]

Hi Mathew,

You can check the VIRGO installation steps documented here:

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

[Ayushman Tripathi]

Hi Alex,

Yes! :) If it was too easy, then no fun 🙂

Thanks!

Sent from my iPhone

On 14 Apr 2026, at 01:14, Ayushman Tripathi <ayushmantr...@gmail.com> wrote:



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