Small Radio Telescope
Ron Fleshman KB2VIV
A small satellite dish is being used as a small radio telescope operating in the 12 Ghz band. The dish, its LNB and a
simple total power detector and power supply are all that is being used at the present time. In radio astronomy, the
received signals are very weak. ; Because the dish is only 24 inches it can only detect strong signals like the sun or the
moon. Its size makes it a great teaching tool. It is portable and can be moved for demonstrations. It is an inexpensive
and easy way to discover Radio Astronomy.
C1-C4 .01mfd L1,L2 100 microhenery D1,D2 1N34 diodes R2; 10k linear pot C6,C7 .1mfd C5 R1 68k
The circuit shown above is the total power detector and AD converter for the telescope. The parts are available from
digikey. I had the old receiver so I could measure the power to the LNB, it was 20 volts, so I used a 20 volt supply. C1,C2 ,
and L1 keep the DC voltage out of the detector. D1, D2 form a square law detector. It produces a DC voltage proportional
to the total power received. Diodes D1 and D2 are critical to the sensitivity of the detector. Diodes with a low Vf such as
germanium or schottky are The best choice. Good microwave construction tech are a must. A constant diode temperature
is also important. A to D conversion is done using the maxium max187 chip. Its output goes to a DB25 connector and to
the parallel port of a computer. A logging program such as Radio Sky Pipe than records the results.
|Prototype of power feed and square law detector being assembled for testing