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" nss@mwt.net To: "Gary "Joe" Mayfield" gary_mayfield@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
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