Are these interference fringes?

66 views
Skip to first unread message

andrew....@googlemail.com

unread,
Oct 15, 2025, 4:39:52 PMOct 15
to sara...@googlegroups.com

Anthony

unread,
Oct 15, 2025, 8:45:31 PMOct 15
to Society of Amateur Radio Astronomers
Are you using an amateur radio astronomy interferometer?

Fringes look similar to this, Taurus A:






--
--
You received this message because you are subscribed to the Google
Groups "Society of Amateur Radio Astronomers" group.
To post to this group, send email to sara...@googlegroups.com
To unsubscribe from this group, send email to
sara-list-...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sara-list?hl=en
---
You received this message because you are subscribed to the Google Groups "Society of Amateur Radio Astronomers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sara-list+...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/sara-list/000201dc3e13%24d52896a0%247f79c3e0%24%40googlemail.com.

Mike Otte

unread,
Oct 15, 2025, 9:20:41 PMOct 15
to sara...@googlegroups.com
Your showing spectrum.   Fringes would be power over time.

Mike

--
--
You received this message because you are subscribed to the Google
Groups "Society of Amateur Radio Astronomers" group.
To post to this group, send email to sara...@googlegroups.com
To unsubscribe from this group, send email to
sara-list-...@googlegroups.com
For more options, visit this group at
http://groups.google.com/group/sara-list?hl=en
---
You received this message because you are subscribed to the Google Groups "Society of Amateur Radio Astronomers" group.
To unsubscribe from this group and stop receiving emails from it, send an email to sara-list+...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/sara-list/000201dc3e13%24d52896a0%247f79c3e0%24%40googlemail.com.


--
Mike Otte W9YS

Eduard Mol

unread,
Oct 16, 2025, 1:33:01 AMOct 16
to sara...@googlegroups.com
Hi Andy,
What sort of setup are you using? I see your horizontal axis in your plot is frequency, not time like in Anthony’s plot, is that correct? Interference fringes would occur over time as the source drifts overhead, you would see the background go up and down just like in Anthony’s plot. 

By the way, that interferogram looks really good Anthony, seems like you finally have your interferometer working well! 


Op wo 15 okt 2025 om 22:39 schreef andrew.thornett via Society of Amateur Radio Astronomers <sara...@googlegroups.com>
--

andrew....@googlemail.com

unread,
Oct 16, 2025, 7:22:08 AMOct 16
to sara...@googlegroups.com

Thanks everyone for feedback on my trace – I realise now not interference trace as does not show power over time but rather shows frequency. Learning every day!

Andy

Anthony

unread,
Oct 17, 2025, 8:06:42 PM (14 days ago) Oct 17
to Society of Amateur Radio Astronomers
Yes, that is correct Eduard. Working on detecting fringes from 3C452, but lots of trees and foilage. Hopefully the leaves will drop soon for the season.

Eduard Mol

unread,
Oct 18, 2025, 4:17:00 AM (13 days ago) Oct 18
to sara...@googlegroups.com
Hi Anthony, 
That seems like a faint target- it barely shows up on the Dwingeloo 820MHz images in Aladin Sky Atlas! 
Currently I am doing driftscans of some of the “classical” radio sources like Cassiopeia A and Taurus A. With a single dish it’s possible, but interferometry shows these sources much better. Too bad that it requires another 3 metre dish :-)



Op za 18 okt 2025 om 02:06 schreef Anthony <itpart...@gmail.com>

Anthony

unread,
Oct 18, 2025, 4:48:20 AM (13 days ago) Oct 18
to Society of Amateur Radio Astronomers
Hi Eduard,

I’ve recorded what appears to be a weak or marginal fringe detection from 3C 452, which is near the lower sensitivity limit of my 2-element interferometer (~15–16 Jy).

 The correlated signal is faint but exhibits structure consistent with a low-amplitude fringe as the source crosses the edge of the primary beam. 

To improve sensitivity, I’m making fine adjustments to dish elevation and carefully managing total power and RF gain settings to maximize system response.

 I may need to do some post-processing and stacking, but I’m definitely picking up a weak correlated signal, after multiple nights of observations. I’ll post results once I have something more conclusive to share.

With winter approaching and the foliage thinning out, I’ll have a much better chance of detecting weaker sources. I’ve noticed in past seasons that my system performs significantly better during the winter months when there’s less signal attenuation and scattering from leaves.

James Abshier

unread,
Oct 18, 2025, 1:15:53 PM (13 days ago) Oct 18
to sara...@googlegroups.com

Hi Eduard and Anthony

About 10 years ago I collected fringes from 3C452. It is a rather weak source (11 Jy) compared with Cygnus A. The attached plot shows fringes from a single scan (Bottom Plot), a 12-scan average (Middle Plot) and the 12-scan average low-pass filtered (Top Plot). The system used was a phase switched interferometer with 2x3 meter antennas. Bandwidth was 4 MHz and integration time was 10 seconds.

Jim Abshier

3C452_12scan.jpg

Eduard Mol

unread,
Oct 18, 2025, 2:05:38 PM (13 days ago) Oct 18
to sara...@googlegroups.com
Hi James, 

That’s an impressive detection! I am surprised this can be done with an amateur setup. 

Anthony, have you tried running an FFT over the interferometer recordings? That’s a trick the team at Astropeiler used to detect faint sources at 11 GHz with their 2X 1.2 metre interferometer, see also 



Op za 18 okt 2025 om 19:15 schreef James Abshier <abs...@ameritech.net>

Anthony

unread,
Oct 18, 2025, 2:41:00 PM (13 days ago) Oct 18
to sara...@googlegroups.com

Hi Jim,

That’s great news, and it’s very encouraging to see your plots! I’ve been working on detecting 3C 452 with my own 2-element interferometer, and I’m fairly confident that my system is picking up very faint or marginal fringe structure from the source as well. It’s exciting to see others have successfully detected it, especially given how weak the signal is compared to Cygnus A.

I’m currently using a 4 MHz bandwidth with an Ettus B210 as the receiver front end. The system chain includes Kuhn 142 LNAs and AGO cavity bandpass filters with approximately 1.0 dB insertion loss. I’m running the RF gain at around 60–68 dB to maximize the system response for such a faint source. 

So far, the system remains stable and within linear range, with no signs of clipping. However, I’m still evaluating whether it’s safe and beneficial to push the B210 RF gain up to 70 dB. Marcus Leech may know the answer, as I believe he still provides community support on the B210.

Best,
Anthony


Anthony

unread,
Oct 18, 2025, 5:25:11 PM (13 days ago) Oct 18
to sara...@googlegroups.com

Hi Eduard,

Thanks for pointing me to the Astropeiler method, it's a fantastic reference. I’ve been running my own pipeline built around BAA Seminar output and a custom Python workflow (tp-analysis_v25b.py).

In my most recent observation of 3C 452 on October 14, 2025 (plot attached), the FFT of Corr(I) shows a clear dominant frequency at 0.0169 Hz (SNR ≈ 100), and the fringe envelope has a coherent shape through the transit window. It’s not proof yet, but it’s solid evidence of a weak fringe from 3C 452, right at the edge of my system’s sensitivity.

I’m also expanding my Python script to automatically process and stack multiple TP CSVs from BAA Seminar, to collect more data and stack multiple nights to tighten things up by improving SNR and phase coherence. 

Most likely I will borrow a few ideas from Astropeiler later, but this current approach already gives me a good handle on the signal.

Best,
Anthony


To view this discussion visit https://groups.google.com/d/msgid/sara-list/CAFcm1Q5%3D9150k5fXnqFHj9v1uH_kqtLtQMy501sOHkN%2Bby7OVg%40mail.gmail.com.
3C452.png
Reply all
Reply to author
Forward
0 new messages