Amateur Radio Astronomy

Hydrogen Line Radio Astronomy


In 1945, H C van de Hulst, a Dutchman, first suggested that the 21cm line of atomic hydrogen might be detectable in interstellar space.

However it wasn't until 1951 that H I Ewen working on his doctorate under his supervisor E M Purcell first detected it at Harvard University using a 1.3m by 17m aperture horn antenna some 3.2m long with the best superhet receiver available at the time.

Today, with very low noise amplifiers and USB software defined radios coupled with modern digital encoding and processing algorithms, detection and measurement of galactic hydrogen is possible with very modest means.

This web site describes a basic SDR receiver costing under 200 with scope to extend and improve measurement detail. Analysis software is also linked.

The plot above was derived using home-made software program RAFFT.EXE on a 100 second data file recorded using a 22 element hand-built Yagi antenna with the receiver system shown.
The central spike is a dc offset and VCO noise feature and can be compensated.
It is noted a few spurious points occur at 1419.4, 1420.5 and 1420.8 again probably associated with the SDR.
The receiver has not been frequency calibrated but the hydrogen line components are clearly obvious and compare favourably to that collected by more complex systems.
The ordinate is the result of taking the ratio of signal record to matched load input record.
Further details are in the white papers listed below.


Hydrogen Line Equipment White Papers

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