Ed astro

Yes it does. Putting RF absorbing material in front of the antenna or even using a dummy load will give al ot of thermal noise as well. I tried some of these methods out a few years ago, when I was doing my first hydrogen line observations. Even with the thermal noise they still work, because the thermal noise is broadband while the hydrogen line is not. However, the spectrum was not quite as flat as when frequency or position switching were used.

Hi Victor, When I do hydrogen line observations, I use the frequency switching method to get rid of the SDR artifacts. After taking a hydrogen line spectrum I shift the frequency by about 2 MHz to get a "dark" spectrum. The hydrogen line spectrum is then divided by the frequency switched spectrum. It is not an ideal method, but it works good enough for the hydrogen line because the hydrogen line is a relatively strong signal. There are also other methods of obtaining a dark spectrum, such as covering the antenna with RF absorbing material or pointing the antenna to the ground. Whatever method you choose, the spectrum will often have a residual slope. You can then fit a line through the parts of the spectrum which do not contain the hydrogen line signal, and divide the. Using an "empty" part of the sky is indeed not a very good method (at least not for hydrigen line), because the hydrogen line is literally everywhere. I think the "mask" in the Virgo code is used to define where the standard deviation of the noise in the spectrum (for calculating the signal to noise ratio) is calculated. This has to be done in the parts of the spectrum away from the hydrogen line, so the mask defines which parts of the spectrum should not contain any hydrogen line signal.

Well I have some experience with radio, I did my first detection of the hydrogen line two and a half years ago, in june 2018. It is always great to see more amateur astronomers working on radio astronomy/ hydrogen line detection.

Hi all, Thank you all very much for the warm welcome! That dish in my avatar is indeed my radio telescope. it is a 3 metre dish which was built in december 2017 for a high school project by me and two of my friends. My father, who is a radio amateur, helped us a lot with all the electronics. I definitely would like to visit Jodrell Bank at some point. I is a very historic site for radio astronomy.

Hi Victor, Nice result! Congratulations! The hydrogen line is at 1420.405752 MHz, and the main peak in your spectrum seems to be really close to that frequency. So I think the frequency offset is at most a few tens of KHz instead of 350-400 KHz Anyway, well done and keep up the good work. Best regards, Eduard

Hi all, I made my SGL account back in March but I have not really posted anything here until now. Today I finally decided to say hello. I do some visual observing and astrophotography from my light polluted backyard, but my main interest is in radio astronomy. After all, radio telescopes are not affected by clouds and light pollution! (There is of course radio interference- but that's another story...)