From the very beginning my goal was to get performance of offset antenna (in my case it was 1,8m Prodelin) better by making it work as a Gregory-type (with ellipsoidal sub-reflector). I've read that Gregory-type systems perform better than offset antennas as they use more effectively surface of main dish and also exclude X-pol. So, I got sub-reflector from factory made Gregory and made proper mechanical fittings. Of course, to make conclusions on which setup is working better we need to do some comparison-tests. For tests I took several LNBs:
- Inverto Black Ultra (white label, some people say that there is difference between performance of IBU with white and red label);
- IBU red label;
- IBU red label adopted by one company for antennas with 70* illumination angle;
- IBU red label 90* illumination;
- Gold LNB adopted to work with original Prodelin feedhorn;
- Invacom single attached to Gregory feedhorn;
- Octagon twin attached to Gregory feedhorn;
- IBU red attached to Gregory feedhorn;
I measured signal levels on all available in my area frequencies from Eutelsat @ 28,2*E (could be any) and put data in spreadsheet. I've got 58 transponders. Then I calculated average signal level.
So, after all this I can say that Gregory systems performing better than usual offset dish. And, secondly, by attaching sub-reflector to offset antenna is possible to get better performance of system. It is like you change 1,8m antenna to 2 meter.
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