Some comments after watching last RTOP

[Stephen Arbogast]

I  would  like  to  make   some  comments  concerning   Discovery Dish   and  Pablo's experience   with  it.    I  too  have been using the  Discovery Dish with  Hydrogen  line  feed  for   some  time  now     and even  though it   is  70  cm  it  works!

1.  Maybe SARA should   consider recommending it   instead of   the  current     dish in a box  for  beginners?

2. Pablo   seems  very  interested in an  array of  dishes..   so  am  I.   But   first    I  would  recommend   to  watch   Marcus Leech's  video's  on YouTube    baa_seminar  it  is  very  good He   addresses the  problems  and  challenges.

I  finally   figured   out  some things   to reduce RFI   from my  Dell monitor  and   my   Orange  Pi  5   Plus  ..  aluminum  foil  on back of  my  Del   monitor  and  turning  my  Orange Pi 5 Plus  at  45  degrees  to my   dish  ....  results using  baa_seminar   with   one  dish.....

[Alex P]

Stephen,

How about doing an eval of the Discovery Dish 's Performance

Use SDR# > IFavg to save a few hour duration 5 min/average drift scan set through of a bright MW H1 region ...

Currently, the easy one is  Dec +20  @ RA 06:15   (  ~ 11:00 AM Local Times )

Copy/paste the IFavg *.txt files into the Excel Template and post the highest ..  ( to be attached.) 

         SDR# > IFavg > Excel

This is a simplified one frame process similar to the HLine3D code, 

     and creates a 'standardized' plot of HLine vs ColdSky in dB

Alex

[b alex pettit jr]

Excel Template Attached 

[b alex pettit jr]

THIS would  be an interesting study :

Add a window screen extender to change the dish from its stock f/D = 0.35  to  f/D = 0.25.

This should improve both the S/N  &  reduce RFI  as it will better shield the dipole feed from Ground Noise & Local RF Emitters.

scales = increments of  10 cm

[tedcl...@gmail.com]

GNU Training Seminar Unpacking the mysteries of GNU Radio
RAG Zoom Sep 18, 2021
Marcus Leech;  a leading authority on GNU for Radio Astronomers.
https://www.youtube.com/watch?v=2awvu_p2-yE

GNU II Training seminar - Unpacking more mysteries of GNU Radio
RAG Zoom Jan 15 2022
Marcus Leach  - Canadian Centre for Experimental Radio Astronomy
https://www.youtube.com/watch?v=_3vkEIYs7gk

      and the code is on github:
      https://github.com/ccera-astro/baa_seminar
...

On Tuesday, August 5, 2025 at 9:47:35 PM UTC-6 Stephen Arbogast wrote:

...

2. Pablo   seems  very  interested in an  array of  dishes..   so  am  I.   But   first    I  would  recommend   to  watch   Marcus Leech's  video's  on YouTube    baa_seminar  it  is  very  good He   addresses the  problems  and  challenges.

...

 

[Stephen Arbogast]

Alex  P.

Yes this  would  be  an interesting  study...   I'm   caught up in a  fascination  with  GNU Radio  Companion and  how  we can optimize  our  data  collection    both  hardware   and  software.    I have  been working   with  both

hard ware  and software    for  many years.    At the moment   I am working   on a GNU  radio  flow    graph  as possible   front  end replacement for  Python..   at suggestion   from  Ted  Cline.  I am  studying   Marcus  Leech's   baa_seminar  software .. I  think  it is the  right  approach   to use   GNU Radio  for    front  end data  gathering...   I am not   an  expert   but  do  have  some  experience in  digital  signal processing.....   GNU  radio  has   built  in    multi-thread management  and    ring  buffer  management.  Then   any one    can use  whatever  they prefer  for back end processing....  the  gathered   data    such as ezRA....  cool  stuff. 

Yes, as  Marcus   Leech said   there is a  large  learning  curve...  but  it  is  well worth it.

Thoughts?   Any  one  else  working  on  this?

[b alex pettit jr]

The reason I recommend SDR# > IFavg is that I have drift scan data sets using such from a dozen or more RT systems against which to compare the Discovery D.

Using other software = results which can not be correlated.

Alex

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

[Stephen Arbogast]

Yes,  I agree.....   I  am  familiar  with that  on  windows.   I have some  recordings  around  here  some where on my  windows  machine... using the   same  software.

This   is  a  problem  in   our  community.. how  do  we compare results  if we   we all  use  different   software  not    calibrated  to  the  same    standard  if  there is a  standard.  The   sky   changes ..    what is the  standard?

[b alex pettit jr]

 For the past many years and way before ezRA,  SDR#>IFavg Has Been the calibrated standard 

   against which  I can compare my results and that of others who use the same.

I found a drift scan fileset from 10Sept 2021.

It can be processed via HL3D and am confident its scaling ===  that of what I capture today. 

I wrote a software pkg in Matlab, and then converted the basics of that (with large bit of help) into Java.

                                          Matlab

I have a collection of > 100 drift scans spanning 5 years  from my configs and that of several others.

So, for my purposes of antenna development, SDR#>IFavg is the 'standard' for HLine data acq .

    Alex Pettit

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

[Marcus D. Leech]

On 2025-08-09 06:09, 'b alex pettit jr' via Society of Amateur Radio Astronomers wrote:

 For the past many years and way before ezRA,  SDR#>IFavg Has Been the calibrated standard 

   against which  I can compare my results and that of others who use the same.

You keep using that phrase "calibrated".  Against what?  Unless you calibrate your instrument against a known laboratory calibration standard
  then it is *un-calibrated*.  No amount of reading the data sheets of a radios components and then doing a simple mathematical derivation
  based on the "typical values" from the data-sheet causes your device to be "calibrated".

Please explain what you mean by "calibrated" in this context, because I'm pretty sure that you aren't using it in the same sense that the
  rest of the world uses it.

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[b alex pettit jr]

not necessarily the World ... but not in K Noise Temp 

For antenna testing purposes: 

1) Having the data plotted in dB referenced to the Cold_Sky Background 

2) Verify the dB units reflect the correct change in signal level   .

Alex P

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

[Marcus D. Leech]

On 2025-08-09 09:23, 'b alex pettit jr' via Society of Amateur Radio Astronomers wrote:

not necessarily the World ... but not in K Noise Temp 

For antenna testing purposes: 

1) Having the data plotted in dB referenced to the Cold_Sky Background 

2) Verify the dB units reflect the correct change in signal level   .

The only way that "dB units" would NOT reflect the correct change in signal level would be if:

  (A) The hardware is being used in a non-linear operating range
  (B) Somehow the math libraries (the same ones that everyone uses), despite having *decades* of rigorous use in
        scientific circles, were somehow *broken*.

Unless you can show that somehow SDR#/IFAvg have implementations of basic operations like FFT, multiply and log10 that  are demonstrably
  superior in significant ways, then ANY DSP chain that does this stuff will produce comparable results, given the same hardware inputs.

Yes, I "get" that you like SDR#/IFAvg, as do many other people.  Many other people choose different pathways for their hobby, and Gnu Radio is
  part of that for them.

The question of "how do we directly compare our data" is orthogonal to the question of "which software should we choose".   Professionals have had this
  problem as well.  Particularly in the field of pulsars, where every observatory "rolled their own" in terms of both equipment and data formats.  To a certain
  extent this is solved now with FITS and PSRFITS.

Alex P

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

On Saturday, August 9, 2025 at 09:14:03 AM EDT, Marcus D. Leech <patchv...@gmail.com> wrote:

On 2025-08-09 06:09, 'b alex pettit jr' via Society of Amateur Radio Astronomers wrote:

Please explain what you mean by "calibrated" in this context, because I'm pretty sure that you aren't using it in the same sense that the
  rest of the world uses it.

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[b alex pettit jr]

I am referring to the plots which scale the data in "Relative RMS Power" or "RMS relative to Maximum" or thereabouts.

These can't be used to eval the Hardware

Alex

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

[b alex pettit jr]

As ROM as it may be, this has shown the SDR#>IFavg process is "reasonably"  linear and properly scaled over the range of normal HLine acquisition.

[Marcus D. Leech]

On 2025-08-09 10:10, 'b alex pettit jr' via Society of Amateur Radio Astronomers wrote:

I am referring to the plots which scale the data in "Relative RMS Power" or "RMS relative to Maximum" or thereabouts.

These can't be used to eval the Hardware

Alex

If your hardware + DSP produces an H1 signal from some fixed location that is 2dB off the notional noise-floor, and some other
  hardware + DSP produces and H1 signal that is also 2dB off their noise-floor, then they are comparable.

The ONLY way to get absolute measurements is with a calibration standard.  There is no essential change in the *information content*
  whether you subtract-out the cold-sky measurement in "real time", or "post facto".  Precisely the same information is conveyed.

Speaking only for BAA_Seminar, it does have a background-subtraction option.  So if you line it up on some "empty" part of the sky,
  let it chew for a bit, and then enable the "Apply Background Subtration" control, it will subtract out its background estimate prior
  to display.    Due to inherent systemic gain drift, I find this is usually only "valid" for shorter periods.   It has been on my "list" to
  allow a background estimate to be loaded in from an external file.  But again, deployed-system gain drift (and even filter shape drift)
  makes this something that requires constant attention.

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[Marcus D. Leech]

On 2025-08-09 10:22, 'b alex pettit jr' via Society of Amateur Radio Astronomers wrote:

As ROM as it may be, this has shown the SDR#>IFavg process is "reasonably"  linear and properly scaled over the range of normal HLine acquisition.

If there's software out there that cannot faithfully reproduce attenuation steps given linearly-operating hardware, then it is broken, or has an
 inadvertent bug.

I'm not aware of any, but I haven't personally evaluated other folks software in this space.  I CAN state that Gnu Radio implementations of
  FFT and log10 have been rigorously 'shaken out' in the last 20 years or so, and indeed, the underlying FFTW3 implementation of FFT has an
  even longer (30+ years) history.

On Saturday, August 9, 2025 at 10:10:09 AM EDT, 'b alex pettit jr' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

I am referring to the plots which scale the data in "Relative RMS Power" or "RMS relative to Maximum" or thereabouts.

These can't be used to eval the Hardware

Alex

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

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[b alex pettit jr]

Hi Marcus

1) " I'm not aware of any, but I haven't personally evaluated other folks software in this space."

Nor have I seen a verification of this .

2) The post test HLine3D code allow the user to identify "cold sky" regions and

specify low and high % of the freq range for frame by frame 2 pt  mx+b background normalization. 

( It averages 20 FFT values around the selected % , finds the lowest of the data set,  and adjust all to that )

Regards,

Alex P

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

[Stephen Arbogast]

I have been exploring  this  stuff  for  several  years now  and  in my opinion  there are  a lot  of good  software packages  for   evaluating  the  data  that  we collect..  this  is not  the  problem.  The  problem  is  we are   struggling  to  collect  the best data that  we  can  for  our  existing   software...in the  amateur   space.. using  hardware within  our  budget  constraints.

???

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[Stephen Arbogast]

Let's  consider   the  real problem we are  facing....  noise...  It is  the real  problem...   here  is   a tutorial  I  found  helpful.......   https://github.com/spatialaudio/digital-signal-processing-lecture

Our  struggle  is  Physics  and    budgets....

[Stephen Arbogast]

I once  stopped   a  fist  fight  between  two  software developers   over who had the   best software....     think  about it....

[b alex pettit jr]

1) Improve your hardware to optimize the received signal strength

2) Acquire averages of sufficiently long duration to provide good statistical convergence of the low signal levels above the system/sky noise.

                    =      Unfiltered 300 Seconds

> There are Many more variables to Stable Hydrogen Line Radio Astronomy Data Acquisition than " Noise"  alone

                        Prof Pettit

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

On Sunday, August 10, 2025 at 11:06:56 PM EDT, 'Stephen Arbogast' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Let's  consider   the  real problem we are  facing....  noise...  It is  the real  problem...  ...............

[Stephen Arbogast]

I  am here  to  enjoy  my hobby.    I love learning  about the   Universe .. So    I  don't   have the  perfect   hardware    and software but I  am  close within my  budget ..    RTL-SDR     and AirSpyR2..  I have been  trying   many  software packages.       I  prefer   the  software    written by   Marcus  Leech...  GNU Radio  ...This  is my   choice  but  may not  be   the best    for novices   just starting  out..     requires    some   knowledge of  building     the ra_funcs lib and installing and some   experience   with  digital  signal  processing    So  I would   suggest  for  a  Novice   start with  ezRA.      When you  are ready   this is a very good way to learn digital signal processing...   https://github.com/spatialaudio/digital-signal-processing-lecture

Stephen

[cretaceou...@gmail.com]

Folks:

This link …

<https://www.wdtv.com/2025/08/06/green-bank-observatory-allows-wifi-their-quiet-zone-first-time/?fbclid=IwQ0xDSwMAswVjbGNrAwCzAGV4dG4DYWVtAjExAAEewCEuTTHaQGSMSRvCKl1xqdtgiBsSNYeJ_djA4RxSd5CqHGw-vNSksZ0WHOU_aem_tO_CJmICayTf2mtwOILTxQ>

leads to a story about the radio quiet zone around Green Bank WV.

I will admit that this is the first I have heard about this "new source
of" QRM near the telescope.

Clear skies and gentle breezes,
tdj

--
Take care,
Tom Jacobs

Wilmington, North Carolina
mailto:cretaceou...@gmail.com
KD4BFQ


He that knows not and knows that
he knows not is a child, teach him.

He that knows not and knows not that
he knows not is a fool, shun him.
He that knows and knows not that
he knows is asleep, wake him.
He that knows and knows that
he knows is a teacher, follow him.
-- Persian Proverb

[Jim Brown]

I met the RFI guy at Green Bank. His job was to go find sources and stop them. In a few cases they made Faraday cages for microwave ovens. In one instance he tracked it down to an electric blanket a woman had put in her dogs doghouse.
JB



Sent from my iPhone

> On Aug 11, 2025, at 9:38 AM, cretaceou...@gmail.com wrote:
>
> Folks:

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[Pablo Lewin]

Hi Stephen and all 

Thanks for the thoughtful and in-depth discussion — it's really fascinating and inspiring to see the expertise here.

Just to clarify my goal wasn’t to weigh in on the technical merits of SDR# vs GNU Radio or calibration standards. I'm definitely not an expert in signal processing or radio astronomy software — I'm more of a curious tinkerer.

What I am hoping to explore is whether there's a path for us “amateur amateurs” to build a kind of grassroots community around the Discovery Dish, maybe even scaling up to dozens or hundreds of users across the U.S. and globally. Then — and this is just a speculative idea — we could pool data after the fact (not in real-time) and see if it’s even theoretically possible to do some form of delayed/interpolated interferometry. I know that kind of synchronization is a huge technical lift in live systems, but maybe some simplified version could be done post-capture?

Anyway, here’s a little video I put together showing two Discovery Dishes in action — one tuned to the hydrogen line with an LNA, and the other receiving satellite weather images from GOES-18. It’s running on a 12-year-old Windows 10 laptop — just having fun and learning as I go.

https://www.youtube.com/watch?v=2boPw22RoUo

Appreciate all the insights shared here and looking forward to learning more from everyone!

Best,

Pablo WA6RSV

[Marcus D. Leech]

On 2025-08-12 13:28, Pablo Lewin wrote:

Hi Stephen and all 

Thanks for the thoughtful and in-depth discussion — it's really fascinating and inspiring to see the expertise here.

Just to clarify my goal wasn’t to weigh in on the technical merits of SDR# vs GNU Radio or calibration standards. I'm definitely not an expert in signal processing or radio astronomy software — I'm more of a curious tinkerer.

What I am hoping to explore is whether there's a path for us “amateur amateurs” to build a kind of grassroots community around the Discovery Dish, maybe even scaling up to dozens or hundreds of users across the U.S. and globally. Then — and this is just a speculative idea — we could pool data after the fact (not in real-time) and see if it’s even theoretically possible to do some form of delayed/interpolated interferometry. I know that kind of synchronization is a huge technical lift in live systems, but maybe some simplified version could be done post-capture?

Not in a way that produces interferometry data.  What you *can* do is do simple post-detection "stacking" of results, and the SNR of those results improve with the square-root
  of the number of observations.   Since these dishes are so darned small, you won't see much improvement over simply having a single larger dish until you have really a lot
  of participants.

But interferometry requires not only time-synch of the recorded data (the easy part), it also requires mutual phase coherence of the receivers over useful time-scales.   If the receivers
  weren't meaningfully coherent when the recordings were made, no amount of post-recording "futzing about" can make fringes pop out of the data.  It might be tempting to do
  intensity interferometry, where data streams are correlated after the detector stage, and it doesn't require phase-coherence.  The issue with *THAT* is that the resulting
  "fringe" amplitudes diminish rapidly with the length of the baseline.  There's no "VLBI Intensity Interferometry" for this reason.  After Jennison and friends invented
  intensity interferometry, events overtook their results, as coherent receiver setups became possible, and phase-coherent interferometry produced vastly better scientific results.

Anyway, here’s a little video I put together showing two Discovery Dishes in action — one tuned to the hydrogen line with an LNA, and the other receiving satellite weather images from GOES-18. It’s running on a 12-year-old Windows 10 laptop — just having fun and learning as I go.

https://www.youtube.com/watch?v=2boPw22RoUo

Appreciate all the insights shared here and looking forward to learning more from everyone!

Best,

Pablo WA6RSV

On Tuesday, August 5, 2025 at 8:47:35 PM UTC-7 Stephen Arbogast wrote:

I  would  like  to  make   some  comments  concerning   Discovery Dish   and  Pablo's experience   with  it.    I  too  have been using the  Discovery Dish with  Hydrogen  line  feed  for   some  time  now     and even  though it   is  70  cm  it  works!

1.  Maybe SARA should   consider recommending it   instead of   the  current     dish in a box  for  beginners?

2. Pablo   seems  very  interested in an  array of  dishes..   so  am  I.   But   first    I  would  recommend   to  watch   Marcus Leech's  video's  on YouTube    baa_seminar  it  is  very  good He   addresses the  problems  and  challenges.

I  finally   figured   out  some things   to reduce RFI   from my  Dell monitor  and   my   Orange  Pi  5   Plus  ..  aluminum  foil  on back of  my  Del   monitor  and  turning  my  Orange Pi 5 Plus  at  45  degrees  to my   dish  ....  results using  baa_seminar   with   one  dish.....

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[Pablo Lewin]

Hi Marcus,

Thanks so much for that clear and detailed explanation — that really helped put things in perspective.

Given what you said about the limitations of post-detection correlation and the challenges of achieving mutual phase coherence, I now see that true interferometry — in the classical sense — is likely off the table for a decentralized, low-budget amateur network like what I had in mind.

That said, I’m still curious: if we did manage to organize a distributed network of, say, hundreds of these small Discovery Dishes, each contributing time-synchronized (but not phase-coherent) data, what could we realistically hope to detect or improve on?

Would pooling results — even if limited to stacking or averaging intensities — help in detecting very faint or transient sources like pulsars, assuming enough averaging and consistent data formatting? Or are we still fundamentally limited by the small effective aperture and the lack of coherence?

Appreciate any further insights — I’m just trying to get a clearer picture of where the real boundary lines are for collaborative amateur work in this space.

Best,

Pablo Lewin WA6RSV

[fasleitung3]

Hi Pablo,

If one puts some numbers behind the collecting area of multiple Discovery Dishes the limitations of this approach become apparent:

At 70cm diamter the Discovery Dish has a collecting area of a bit over 0.38 square meters. A 3-m dish, which is still in the realm of possibility for amateurs, has about 18 times more collecting area. If one really wants to go beyond this like a 10-m equivalent, you already need ~ 200 Discovery Dishes. To have an equivalent collecting area to our 25-m dish you need 1275 Discovery Dishes.

I would assume that one runs very quickly into practical limitations to get so many parties interested, organized and coordinated over a sufficiently long period of time.

Combing the data from many small dishes will be fairly easy for tasks like collecting hydrogen spectra. In such a scenario, each site can collect data independently and later stacked in post processing. For pulsars, things get already quite complex: Absolute timing precision has to be around 1/10th of the pulse width to allow stacking of the data. Also, the spectral resolution from each instrument needs to be the same and preferably all should have the same bandwidth.

Best regards,

Wolfgang

[b alex pettit jr]

Hello Wolfgang,

From my experience  " getting so many parties interested " is the insurmountable issue.

Obviously more dishes would equate to simultaneous  averaging for improving the Quality of the data ( statistical convergence )

BUT How would you combine the data to increase the Angular Resolution as would be obtained with a larger diameter Dish ?

Regards,

  Alex Pettit

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[fasleitung3]

Am Mittwoch, den 13.08.2025, 09:24 +0000 schrieb 'b alex pettit jr' via
Society of Amateur Radio Astronomers:

>
> BUT How would you combine the data to increase the Angular Resolution
> as would be obtained with a larger diameter Dish ?
>
>

Obviously there is no improvment in angular resolution (unless you go
to VLBI schemes). So it is sensitivity only.

[b alex pettit jr]

Hi Wolfgang,

I anticipated this to be the case... just wanted to verify .

Cheers,

Alex

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[Pablo Lewin]

Hi Wolfgang,

Thank you for putting the numbers into perspective — that’s exactly the kind of practical framework I want to build on.

My thought isn’t to replace a 25-meter dish, but to figure out what can be done with an array of smaller, widely distributed amateur instruments. Even if each Discovery Dish has only ~0.38 m² collecting area, 10, 100, or 1,000 of them — while not VLBI-grade interferometry — could still open the door to:

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1. Hydrogen Line & Spectral Surveys

• As you mentioned, hydrogen spectra stacking is straightforward.

• An array like this could produce all-sky hydrogen maps updated frequently, useful for teaching, public outreach, and citizen science contributions to long-term monitoring.

• Distributed small dishes could monitor variations in neutral hydrogen emissions over months or years.

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2. Pulsar Timing Projects (with Some Standardization)

• With modest investment in GPS-disciplined oscillators and agreed-upon bandwidth settings, even small dishes could participate in a coordinated pulsar timing campaign.

• Instead of high-end professional precision, the aim could be to extend the time coverage — filling in observing gaps that professional observatories can’t cover.

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3. Transient Event Monitoring

• Small dishes can act as a global network of “alert ears” — detecting unusual signals or flux changes, then alerting larger facilities.

• This includes supernova radio afterglows, bright bursts from known pulsars, and potential SETI candidate re-detections.

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4. Educational Integration

• Schools, universities, and community clubs could “adopt a sky patch” and contribute data to a central repository.

• This transforms amateur radio astronomy from a spectator sport into hands-on participation, even for low-budget institutions.

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5. Long-term Monitoring

• A large, persistent network could track variable sources (AGN, flare stars, X-ray binary radio counterparts) at flux levels detectable with small apertures — especially if signals are integrated over long periods.

• The advantage here isn’t sheer sensitivity but continuous coverage across many longitudes.

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If the scope is clearly defined — hydrogen mapping, bright pulsar timing, transient alerts, education — the coordination challenges become manageable, and even 10 to 100 dishes could make meaningful, publishable contributions.

What do you think about developing a minimum technical spec (bandwidth, timing, calibration) so we can test a small pilot network before scaling up?

Best,
Pablo