Radio observation in hydrogen line (1420MHz)

Trying to work out why my 1420MHz AD8302-based radio interferometer does not work

Unfortunately, I still can’t get my 1420MHz interferometer to work.

Have received 2 excellent pieces of advice from Jan Lustrip and Mike Otte, pasted below – today I have made first step in following their process to get to the bottom of the problem – without changing any other aspect of my system, I handheld each aerial (Nooelec mesh 60x100cm 1420MHz dish) by its supporting stalk and pointed it at the the sun whilst leaving the other aerial pointed at open sky. The scan results from this test are shown below Jan’s and Mike’s advice.


I do not see any fringes…

To make sure all is working do a solar drift scan with each antenna and check that they show the same Sun transit hump. Use the VM output for this. If you do not see any sun transit on any of the antennas then something is wrong in your setup somewhere. If you see nice solar transit then your sensitivity is good., then the fault must be in your AD8302 chip in the Phase VP part, in which case try to replace the AD8302 to confirm.



The Sun is a very strong source but surprisingly not real strong at the hydrogen frequency. The Nooelec SAWbird H1 filter is the only real “tuning”, but they are 50+ Mhz wide so you should have lots of signal. With a meter hooked to the magnitude output (VMax) of the AD8302, you should be able to sweep the antenna back and forth through the Sun and see it go up and down in value. You don’t have to wait for noon. For the Sun I do not think you need 3 serial SAWbirds on the antenna. One should be enough. See if the white light is “on” on the saw bird   and the red light  is “on” on the ad8302. Check every connection by taking them apart and inspecting  for  missing pin, lose parts. Use the meter and check for shorts and opens and that no pieces missing. You have lots of connections , check them all.  Get a buddy to look at it ,  check the “in’s” and “out’s” are on the right side. “Divide and Conquer!”, Good Luck!


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