My Interfeometer sutup

[Jan Lustrup]

Here is a drawing of my Multiplying Interferometer setup for 21cm.

With just a single 2meter dish I could only detect less then a handful of radio sources…..but with this two dish multiplying interferometer setup I have detected 36 radio sources and counting! The weakest ones just below 10 Jansky @ 1425MHz.

One big problem with my small dishes is separating several sources that are close together and the fringes interact due to the broad main lobes.

 

Clear skies,

Jan Lustrup – LA3EQ

Norway

 

 

[ja...@ganssle.com]

Jan,

 

Very interesting! Any chance you could write this up for the SARA Journal?

 

Jack

N3ALO

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[Captain Anne Flint]

Nice drawing Jan! Wende 

On Nov 17, 2025, at 7:23 AM, 'Jan Lustrup' via Society of Amateur Radio Astronomers <sara...@googlegroups.com> wrote:

Here is a drawing of my Multiplying Interferometer setup for 21cm.

With just a single 2meter dish I could only detect less then a handful of radio sources…..but with this two dish multiplying interferometer setup I have detected 36 radio sources and counting! The weakest ones just below 10 Jansky @ 1425MHz.

One big problem with my small dishes is separating several sources that are close together and the fringes interact due to the broad main lobes.

 

Clear skies, 

Jan Lustrup – LA3EQ

Norway

 

<image001.jpg>

 

[Eduard Mol]

Nice work Jan! 

Seeing radio sources down to <10 Jy is really impressive!

Whenever I see these interferometer projects my hands are itching to build one myself… then I realise I already have too many other projects going on and lack the technical skills for such a complex build 😅

Op ma 17 nov 2025 om 14:23 schreef 'Jan Lustrup' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

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[James Abshier]

Jan - I have a couple of questions about your use of the AD8362 detector. Are you using one of those modules available through Amazon? My understanding of the AD8362 is that the output is normally logarithmic in power rather than linear in power. Although that would certainly work, it seems like the fringe signal gain would depend on system noise level and calibration could be problematical. If you are using one of those modules, does it allow you to get linear rather than log output?

Congratulations on detecting sources down to 10 Janskeys. I am still running my 1400 MHz phase switched interferometer. A few years ago I had to give up using one of my 3 meter dishes and substituted a smaller out-rigger dish. To partially compensate for the loss in sensitivity, I built a 25 MHz bandwidth receiver to replace the 4 MHz one that I had been using. I also started switching both antenna signals with quadrature phase switching signals. This approach doesn't improve sensitivity but it prevents switching signal ground currents from affecting synchronous detector output.

Jim Abshier

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[Anthony]

I can never get enough of admiring your interferometer, Jan! The configuration and setup look absolutely fantastic. 

Truly great work!  😄

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[Jan Lustrup]

Here are two weak Radio Galaxy sources detected on my 21cm interferometer.

The graph shows “3C111” that is a 15 Jansky source (@1420MHz) and “3C134” a 10 Jansky source (@1420MHz).

Going below 10 Jansky levels is possible, but you need a lot of averaging and good imagination!

Jan Lustrup LA3EQ

Norway

 

 

From: 'Jan Lustrup' via Society of Amateur Radio Astronomers [mailto:sara...@googlegroups.com]
Sent: mandag 17. november 2025 14:24
To: sara-list@googlegroups. com
Subject: [SARA] My Interfeometer sutup

 

Here is a drawing of my Multiplying Interferometer setup for 21cm.

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[wallacefj]

Impressive! Do you deconvolve your data or just seeking detection?

Thanks again for all the information!

Sent from my Verizon, Samsung Galaxy smartphone

To view this discussion visit https://groups.google.com/d/msgid/sara-list/003001dc5880%242b417300%2481c45900%24%40no.

[Jan Lustrup]

I just seek detection and confirmation by doing several observation runs , correlate fringe rate to known declination* & transit times and then add the data (Date and time, RA, Dec, elevation, fringe rate, fringe voltage, Flux  etc) to an excel logbook of  my detections.

Then I try detecting weaker and weaker sources, by improving equipment etc.

This is a little like ham radio as we enjoying collecting QSL card confirmation reports from DX (distant locations) around the world.

 

* Comfirmation of a source declination by fringe rate is some times very challenging with small dish antennas.

Using small antenna dishes when sources are close together in the sky it get tricky. While two or more sources are simultaneously present within the antenna beams, they produce fringe oscillations with slightly different frequencies, resulting from differences in the source declinations. Maxima in the fringe amplitude, which occur when the fringe components happen to combine in phase, can mimic responses to other sources. Many sources are close together near the milky way center and telling them apart is not easy.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/LKSxvtWbrwwxNLKSzvemip.1763467551.19defe116147f6efed23c059576ea3b0.MISSINGID%40comcast.net.

[Jon Wallace]

Thanks again for all the additional information!

To view this discussion visit https://groups.google.com/d/msgid/sara-list/004c01dc5895%24e08b9e10%24a1a2da30%24%40no.

[Eduard Mol]

Hi Jan, have you tried running an FFT over the fringe data? That should give you an accurate measurement of the fringe period. Maybe you can use it to tell apart sources that overlap in the main beam but which have different declinations. The wonderful folks at Astropeiler also used this trick with their 2X1.2m Ku band interferometer, see also  

https://www.astropeiler.de/en/info-zum-2-x-12-meter-interferometer/

 and 

https://jufo.stmg.de/2014/Radiointerferometer/Radiointerferometer.pdf 

Op di 18 nov 2025 om 15:16 schreef 'Jan Lustrup' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

To view this discussion visit https://groups.google.com/d/msgid/sara-list/004c01dc5895%24e08b9e10%24a1a2da30%24%40no.

[kshoe...@aol.com]

Greetings,

Can you add Shoema...@gmail.com  to your mailing list?

Thank you

-Kevin

To view this discussion visit https://groups.google.com/d/msgid/sara-list/CAFcm1Q6zMcM0BDSshCjib%2B9kXdBrdF17__RoQBzdh3J2pottgw%40mail.gmail.com.

[edhar...@gmail.com]

Is this a secondary address for you?  If so, you can modify your Google profile.

 

If this is for someone else, please have them join the group through the normal join option.

 

(We have enough spammers and hackers that try to join or succeed and try to send trash that I hope you understand our skittish behavior at directly adding people to the group.)

 

Ed H.

Co-moderator

 

From: 'Jan Lustrup' via Society of Amateur Radio Astronomers [mailto:sara...@googlegroups.com]
Sent: mandag 17. november 2025 14:24
To: sara-list@googlegroups. com
Subject: [SARA] My Interfeometer sutup

 

Here is a drawing of my Multiplying Interferometer setup for 21cm.

With just a single 2meter dish I could only detect less then a handful of radio sources…..but with this two dish multiplying interferometer setup I have detected 36 radio sources and counting! The weakest ones just below 10 Jansky @ 1425MHz.

One big problem with my small dishes is separating several sources that are close together and the fringes interact due to the broad main lobes.

 

Clear skies,

Jan Lustrup – LA3EQ

Norway

 

To view this discussion visit https://groups.google.com/d/msgid/sara-list/1931197093.7292940.1763480148776%40mail.yahoo.com.

[Jan Lustrup]

Hi Eduard,

That sounds like a good idea….But how to make a FFT from the fringe data?

Maybe using Spectran, Argo or Speclab?

Jan

 

 

 

 A different problem when using small antenna dishes is when sources are close together in the sky. When two or more sources are simultaneously present within the antenna beams, they produce fringe oscillations with slightly different frequencies, resulting from differences in the source declinations. Maxima in the fringe amplitude, which occur when the fringe components happen to combine in phase, can mimic responses to other sources.

This is a serious problem because the beams of my interferometer antennas were too wide.

 

 

From: sara...@googlegroups.com [mailto:sara...@googlegroups.com] On Behalf Of Eduard Mol
Sent: tirsdag 18. november 2025 15:51
To: sara...@googlegroups.com
Subject: Re: [SARA] My Interfeometer sutup

 

Hi Jan, have you tried running an FFT over the fringe data? That should give you an accurate measurement of the fringe period. Maybe you can use it to tell apart sources that overlap in the main beam but which have different declinations. The wonderful folks at Astropeiler also used this trick with their 2X1.2m Ku band interferometer, see also  

To view this discussion visit https://groups.google.com/d/msgid/sara-list/CAFcm1Q6zMcM0BDSshCjib%2B9kXdBrdF17__RoQBzdh3J2pottgw%40mail.gmail.com.

[Eduard Mol]

Hi Jan, if you have the fringe data saved for example in .csv format there sure is a way to do it with python (or any programming language of your choice for that matter), perhaps with the fftfreq function from Scipy for example?

I have also used Acycle (

https://github.com/mingsongli/acycle

) for FFT and wavelet analysis in the past. This programme was originally intended for analysing geological data to find Milankovitch cycles, but it can take any .csv data file as long as it has a time column (or distance) and a column representing some measured value. After all, an FFT is an FFT regardless of whether it is applied to oxygen isotope measurements or interferometer data ;-)

Maybe you can send me a sample file from your interferometer- if you have one- so I can try FFT analysis on it in Acycle?

Op di 18 nov 2025 om 17:15 schreef 'Jan Lustrup' via Society of Amateur Radio Astronomers <sara...@googlegroups.com>

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[James Abshier]

Jan ,

The attached image was produced from the fringe data shown in the plot by taking a running FFT over a width that is about the same as the extent of the fringes. Starting at some point before the fringes, define a window that is about the same extent as the fringes and take an FFT of the data in the window. Save the FFT data as a column vector for the image. Then shift the window to the next point (which could be several samples ahead) and take an FFT of fringe data in that window. This then becomes the next column of the image. Repeat this procedure to a point beyond the fringes and you will have produced an image with the data compressed in the vertical direction by the FFT and imaged in the horizontal direction at roughly the same resolution of your antenna beam. I think of it as a hybrid aperture synthesis imaging technique. The horizontal axis is right ascension and the vertical axis is declination. I am unaware of any "canned" software that is available for doing this, so you are on your own to code it.

I use octave to process fringe data, but python or anything that includes an FFT function would be appropriate.

Jim Abshier

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[James Morris]

Hi Jan,

Do you have documentation on the theory of operation of this setup? I can kind of figure it out but not fully.

To view this discussion visit https://groups.google.com/d/msgid/sara-list/003001dc5880%242b417300%2481c45900%24%40no.

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James Morris W7TXT

https://w7txt.net/

[Jan Lustrup]

Hi James…

No, I do not…But I can try to “walk you through” any part of the signal chain that is unclear without using heavy math if you want.

Jan

 

From: sara...@googlegroups.com [mailto:sara...@googlegroups.com] On Behalf Of James Morris
Sent: tirsdag 18. november 2025 21:37
To: sara...@googlegroups.com
Subject: Re: [SARA] My Interfeometer sutup

 

Hi Jan,

To view this discussion visit https://groups.google.com/d/msgid/sara-list/CAAJi5p46cEfW2PtHrhpbmySH2o95t8jXgCX-WWDZbRGew888GA%40mail.gmail.com.

[Jan Lustrup]

Instead of a Lock-Amplifier you could use this “Synchronous Demodulator” circuit that works just as well.

C1 is a low leakage unipol type. R1 may range from 470k to 25M depending on your baseline distance & RF frequency used.

 

 

 

From: 'Jan Lustrup' via Society of Amateur Radio Astronomers [mailto:sara...@googlegroups.com]
Sent: mandag 17. november 2025 14:24
To: sara-list@googlegroups. com
Subject: [SARA] My Interfeometer sutup

 

Here is a drawing of my Multiplying Interferometer setup for 21cm.

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