....I agree with Gus. And the difference is 20-30 dB depending upon the construction, reflections, lobes of antennas and other complex parameters.
In general a Cross-Yagi which appears a very good circularity, then rising easily to 30 dB between RHCP-LHCP.
Tim, also keep in mind, by using CP the fading is much less and never the signal has too much "deep" . Having in mind that the LEOs changing quite often the polarization, I believe the switching between RHCP-LHCP is mandatory, if always you looking for good RX-TX conditions . A mere example was the last pass of AO-7 over my QTH . During the ascending orbit it was 5 S-units without preamp and almost close to TCA the signal dropped down to Zero (Q5). By changing my antenna to the opposite polarization, it was again 5 S-units. That is a great difference on receiving.
So, If you want just to play with LEOs and you are not looking for the optimum, you can do it by using stable polarization. However it's compromise and manytimes you will wonder why the satellite is too weak and some other times "booming".
73, Mak SV1BSX
----- Original Message ----- From: "Angus" angus@young5769.freeserve.co.uk To: AMSAT-BB@amsat.org Sent: Friday, September 19, 2008 5:29 PM Subject: [amsat-bb] Re: Polarity questions
if the satellite is running RHCP and you have LHCP the VHF/UHF Manual handbook says 20 -30dB which is a lot! having spent ages getting a homebrew polarity control box to work just right, I can honestly say it was well worth the effort! regards Gus M0IKB ----- Original Message ----- From: "Tim Tapio" tim@timtapio.com To: amsat-bb@amsat.org Sent: Friday, September 19, 2008 1:58 PM Subject: [amsat-bb] Polarity questions
Hi,
How much signal reduction is there as the result of having the wrong circular polarization? I'm looking at M2 circular antennas for the 70cm downlink, it's another $200 for the switching to change polarity (woo hoo).
73 de Tim, K4SHF
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