2014-01-13 3 months ago
I had a look what software is available for predicting satellite passes in the ubuntu ham radio software repositories. PREDICT satellite tracking and orbital prediction program which does all the calculations given recent Keplerian elements which are available from sources like Keplerian elements at Amsat and Current NORAD Two-Line Element Sets at celestrak. Predict comes in two versions: predict in a version from May 2006 and predict-g1yyh. They look a bit different but the calculations are the same in the end. Important part (to me) is the software also does the calculations for doppler shift. Doppler shift does occur measurably in radio signals when the two stations have a high enough speed difference between them. Since amateur radio satellites are low earth orbit satellites, the speed is measured in kilometers per second and the shift is there and should be taken into account. Shifts in the 70cm band are high enough that you need to retune the radio. As visible in the screenshot predict does calculate the frequencies when the satellite is visible. gpredict which is totally not related to predict. In my opinion gpredict has a more modern interface (it's gtk+ based)
but it lacks support for doppler shift. This makes it somewhat less interesting for radio use.