SIDI, Simple digital interferometer for amateur radioastronomy

Sidi Article on EUCARA 2014

for amateur astronomers, simlicity, cost and easy building is essential. Marko - S57UUU designed this device to participate the ERAC (European Radio Astronomy Club)  project aiming to build an amateur VLBI system called ALLBIN. First incarnation of sidi was in 2007, built with TV tuners and connected to the pc on parallel port. Later, USB2 interface was built and bandwidth increased to more than 10MHz. More on project can be found on Marko's page.

On satturday, 8th of March 2014 Marko finished his SIDI 1.2 and has brought it to my place for real-life test, where we set up the antennas to try the transit interferometry.

We used natural slope on the East side, where we hung the antenna to the road fence, the other is on the wheels on the WW2 German Flak.

First attempts of recording the Orion radio sources failed, detailed inspection of the hardware in the following days has shown that transport and inactivity has caused some wires to get loose ;) Marko wrote a bunch of useful software, but we were still not able to detect if both channels are working. For the next version, a signal detector and simple spectrum analyzer for both tuners would be a good idea.

On march 18. 2014 in the evening i managed to fix loose wires in the SIDI, with promising first results. With 30m baseline and two SBFA s53mv 23cm antennas, pointing to south on 1575 GPS frequency, first fringes showed up. After this, the 3m parabolic dishes, pointing exactly to south and 40 deg. of elevation the fringes on GPS band became smooth and clear.


First GPS fringe, 30m baseline, 1575 MHz

25m baseline, 2 x 50cm SBFA antenna


GPS fringes, 3m dish 42m baseline

45m baseline, 2 x 3m parabolic antenna


Encouraged by successful start, i left SIDI running and recording on 1420 MHz over the night. A nice surprise came in the morning, when by coincidence very clear fringes appeared, and stellarium told me, antennas are pointing towards Aquila constellation (somewhere near 18h50 min,  -5 deg).


First fringes from the faint radio source (18h49min, -5deg) near Aquila constellation.

After checking with VizieR site, this is most probably the GM44  at 18 47 38.02    -01 55 32.7 (RA2000, DE2000).

Next day, Orion nebula was recorded with integration of 16M samples. Arrival, maximum and decline are shown in the screenshots.

Orion arrival

More images in galery

In the next days, we started to list the sources recorded, list can be found Radio sources recorded with SIDI.


To do:

- Time scale on graph, slider in time axis

- Radio source power measurement detector