No, Cross polarization in the real world is 20 to 30 db loss. In the theoretical world it's infinite,
http://www.amsat.org/amsat/archive/amsat-bb/200101/msg01220.html Joe WB9SBD Jeff Yanko wrote: > Hi Joe and all, > > I doubt if the Arrow diplexer has 20dB of loss. If it did, we'd never > receive a signal! :) > > I believe somebody here on the -bb will be performing a test on the > Arrow diplexer using a vector/network analyzer. It will be > interesting to say the least. There were preliminary reports saying > the device had a loss anywhere from 2.65 to 2.80dB. That's close > enough to 3dB which is technically half power loss. Add the loss of a > short piece of coax and it will certainly be pushed over the 3dB line. > > If I recall correctly, cross polarity is also a 3dB loss. I have > noticed that when I rotate the antenna I might get a stronger downlink > but I never lose it when I rotate it back. Before, when I would do > that it would drop once I rotated in either direction from the peak > signal. Basically what is going on is the lossy device is removed and > replaced with a more efficient one, that extra net gain you just > boosted now shows how the system on the antenna side of the diplexer > is truly performing. > > I don't have an antenna analysis program to perform a test, but what > does a 7 element 440 yagi pattern look like and what is its overall gain? > > What we need to do is break down the antenna configuration into 3 > segments, see what their losses and gains are then combine them for > the overall figure. The 3 segment would be the antenna, the diplexer > and the coax. Each one will be tested individually to give an accurate > number for each. > > > 73, > > > Jeff WB3JFS > ----- Original Message ----- From: "Joe" <n...@mwt.net> > To: "Gary "Joe" Mayfield" <gary_mayfi...@hotmail.com> > Cc: "'AMSAT-BB'" <amsat-bb@amsat.org> > Sent: Friday, September 25, 2009 6:42 PM > Subject: [amsat-bb] Re: Arrow antenna reconfiguration results - UPDATE > > >> as in the texts below, there is something else going on here. >> >> That Diplexor can not be all that bad. two reasons. >> >> How many db down is the front to side of that antenna? >> >> and I can not imaging someone would sell a diplexor that has greater >> than 20 db of losses. >> >> because of the statement that how criticalpolarity was with the >> original, and now the antenna has to be nearly 90 degrees cross >> polarized to make it drop out uhh >> >> that close to 30 db, >> >> at least 20,, >> >> something else is going on here >> >> Gary "Joe" Mayfield wrote: >> >>>> >>>> Another issue I came across was how wide the beamwidth is of the Arrow >>>> Antenna between the Arrow diplexer and the new diplexer. I was >>>> wondering >>>> >>>> >>> if >>> >>> >>>> this was going to happen and it did. The reason that this happened >>>> was >>>> >>>> >>> with >>> >>> >>>> the old diplexer, the signal attenuated so much that you had to be >>>> pointed >>>> right smack dab on the bird, a few degrees off and you lost the >>>> signal. >>>> Now, with the new diplexer, you can point the beam in the general >>>> >>>> >>> direction >>> >>> >>>> and still copy the bird. In most cases I had to turn the beam 90 >>>> degrees >>>> before I completely lost the downlink! Twisting the antenna to make >>>> polarization changes makes absolutely no difference now. This also >>>> attributes to the fact that now I'm copying the entire pass without >>>> >>>> >>> dropouts >>> >>> >>>> or fades. Makes sense. What I've regained over the lossy diplexer >>>> makes >>>> >>>> >>> up >>> >>> >>>> for any polarization differences, etc. for a better copiable signal. >>>> >>>> Next weekend I will have to try more passes and get a feel of how much >>>> >>>> >>> this >>> >>> >>>> system has changed. >>>> >>>> >>>> 73, >>>> >>>> Jeff WB3JFS >>>> Las Vegas, NV >>>> DM26 >>>> >>>> >>>> >>>> >>>> >>>> >>>> _______________________________________________ >>>> Sent via amsat...@amsat.org. Opinions expressed are those of the >>>> author. >>>> Not an AMSAT-NA member? Join now to support the amateur satellite >>>> program! >>>> Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb >>>> >>>> >>>> >>> >>> _______________________________________________ >>> Sent via amsat...@amsat.org. Opinions expressed are those of the >>> author. >>> Not an AMSAT-NA member? 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