@H_Neil wrote:
First: this isn't completely done but it is working well enough to report on.
I made a helix antenna for L-band and mounted it in the outernet ku-band dish
Here are the main references used:
http://www.uhf-satcom.com/lband/
http://jcoppens.com/ant/helix/calc.en.php
http://www.rtl-sdr.com/building-a-l-band-helical-antenna-for-inmarsat/I was getting the outernet signal 2-4 decibels better than the patch antenna, generally. I wasn't being strict about the testing and was also swapping in different lengths of coax and checking differences between the E4000 and RTL-SDR, and I found out later there was something wrong with the CHIP I was using, so even with all of that messing around the helix-in-dish worked at least as good as the patch.
Notes:
-the outernet signal is RHCP (right hand circularly polarized) which gets reflected in the dish so the helix is LHCP-coax length made a difference. I ended with reusing the 25 ft coax running through the pipe by cutting it down to about 12 feet.
-the better focal point for the helix in the dish seems to be further out than where the LNB was (from just holding it in different positions) so I'm planning on (in a few weeks) extending the arm by about 6-8 inches and adjusting this tuning using SDR#
-I didn't move the dish from pointing at galaxy 19 (the ku-band satellite) to inmarsat since there is only 1 degree difference between them--97 vs 98. I figured if I could get a signal where it was I'd better not mess with it.
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