Radio observation in hydrogen line (1420MHz)

First light on additive interferometer

Experiencing difficulties with my multiplying interferometer (which means it doesn’t work yet!), I am trying a simpler additive interferometer using 2 x Nooelec 1.4GHz dishes, SAWBird+ H1M LNAs at dishes, 5m coax, and 2nd hand mini-PC from ebay (rest from Amazon – just the mini-PC from ebay).

For addition, I am trying a power combiner.

In my kit, I had an appropriate mini-keyboard and screen which works with the mini-PC!

You will notice I initially put the 2 aerials behind each other, then realised should be side-by-side – in my garden 5m about max distance I can have between antenna.

The plot on ezRA’s ezCol collecting software shows a hydrogen peak (this was in back-to-back configuration) – at this point the laptop I was using died and I have not yet tried the mini-PC.

So I have yet to find out what this kit is capable of delivering…..or not!!


4 thoughts on “First light on additive interferometer

  • Michael L Otte

    Certainly the first chance of success is drift scanning the Sun. My first summing interferometer was summed in a “sma tee” and it fed power out to the two Sawbirds too. Yes, you want the dishes on an E-W line. Nothing is as critical as these SARA guys imply. You’ll get fringes even if the antennas aren’t precisely E-W, even if your coaxes aren’t the same length.

    Remember now you are not looking at Hydrogen clouds 1420.406Mhz so another frequency above or below that would work. Also the Sun will give you a strong interference pattern even if it is 30+ degrees near the source you are looking for.

    Interferometry is for positional location of sources not power or spectrum.

    • Thanks Michael – just the advice I need! Brilliant!

      • Melvyn Jones

        Hi Andy,
        I have never built an interferometer but thinking about you system this is how it should work.
        I assume you are trying to see the sun here with the aerials pointing due south so as above you need them on an E-W baseline, ie one aerial by the tree at the bottom of the garden and one by the steps. As the sun tracks across the aerial’s field of view the distance to the two aerials will change, giving a maximum when their outputs are in phase and a minimum when out of phase. So you get a maximum at the output of the combiner at each wavelength difference in the distance .
        I think then you will see repeated peaks at a spacing of sin-1(wavelength/baseline) ie at 21cm and a 5m baseline you would see them at 2.4 degree movement of the sun. This is roughly at 10 minute intervals. Therefore to see the fringes you need to integrate over repeated 2 minute periods then plot the amplitude of each so getting 5 samples per cycle peak-trough-peak.
        This is a very simplified explanation but may be enough to get you started. If anyone disagrees please add to this but I think it is correct.

        • Thanks Melvin for your comments. This is my understanding too. I am using Ted Cline’s marvellous ezRA suite of software in Python – he has walked this path before me and successfully obtained fringes on the Sun with small aerials and I note a recent SARA video where 2 x cantennas successfully were used to get fringes, although that was also using LimeSDR software defined radio to integrate.
          Hopefully will work for me too!


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