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Rx/Tx antennas


Michael P Clark

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A fellow mixer and I was discussing Rx/Tx antennas and orientation. How it's best to have the receiver antennas in the same direction as the transmit antenna for best possible signal. So I looked at his bag, and all of his receiver antennas are bent over due to whatever cause(packing, transport, etc). I know you've seen it, mine did that also. They never keep their shape. Some end up bent together, some splayed apart. Some practical horizontal with enough usage. So I thought I'd bring up the remote audio whip antennas that don't bend. He scoffed, saying way expel more money when it doesn't matter. So I brought up our previous talk about orientation, and pointed out that his antennas were basically flat horizontal(at the ends). His rebuttal was that HAM radio antennas are sometimes placed through trees and up walls at many different angles. So it's not the orientation that matters, but the length! I agree with the length part but orientation should matter. Any thought's? Besides the obvious, and unintended phallic references:)

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I know it's not the be all/end all of information, but a quick search on wikipedia resulted in this:

<i>The "polarization" of an antenna is the orientation of the electric field (E-plane) of the radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation. It has nothing in common with antenna directionality terms: "horizontal", "vertical" and "circular". Thus, a simple straight wire antenna will have one polarization when mounted vertically, and a different polarization when mounted horizontally.</i>

So apparently, it does matter. I have had drop outs cured by repositioning my radio packs, but it's usually only on a long distance transmission that this happens. Higher TX power will also help with this, but there are few choices when it comes to anything over 100mw. I've considered trying to mount my LP antennae on my versa-flex harness, but that raises all kinds of questions in it's own right. I already get enough questions about the gear in the bag, without having aerials sticking up above my head!

Tom

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Lectro's Larry Fisher, the wireless guru supreme, has addressed this over on RAMPS.  The short answer is that in a location (such as interiors) where there is a lot of multipath (the signal bounces all over the place) it doesn't matter as much.  But, where the terrain is clear, and especially at longer distances, orientation makes a big difference -- both should be polarized the same.

I work inside and at close distances a lot, so in my bag, on each diversity pair, I have one vertical and one horizontal.  I can easily remove the elbows on the horizontal ones when necessary.

More critical is not desensitizing your receivers with a transmitter that is too near them.

John Blankenship, CAS

Indianapolis (Home of the Super Bowl Champions!)

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Thanks Tom!

Thanks John! Didn't think about running each antenna in different polarities. I'll have to try that if I run into problems in the future. But my bag looks cleaner with straighter antennas:)

Thanks for the leg work Darren, I guess I should've checked there, also. I knew about that link, but forgot.

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