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ob1

Patch antenna question

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Hi...I have been looking at lots of forums (RCU, RCG, RC-CAM, etc) and reviewing posts about wireless aerial video components, including the "patch" antenna, which seems to be very popular. I have some older 2.4 equipment (+/- 3 yrs) that came with a "whip" rx antenna that is about 8" tall curly wire with magnetic base. It appears this is omni-directional and does not work well (lots of drop-outs) even in a relatively remote and flat area without any obstacles. So I am thinking about getting one of the 4.5"x4.5" 8dbi patch antennas that are comercially available through several wireless hobby sites as well as internet-based electronics vendors.

I have done quite a bit of reading about the electircal and RF properties of the patch-style antennas, and feel like I have a resonably good understanding of how/why they work (but not expert by any stretch). However I do not really understand why some of the "circular polarized" patch antennas are "left polarized" versus "right polarized". What does the "circular" distinction provide in the way of benefits, and what does the "left" and "right" distinction mean technically? And what does it all mean to me in terms of use in the RC wireless video hobby?

Also does anyone have any suggestions about their choices of internet-based electronics suppliers as to good quality and fair price for this style of antenna?....thx

ob1

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What does the "circular" distinction provide in the way of benefits, and what does the "left" and "right" distinction mean technically?

Some installations need the signal rejection they offer. If the polarizations don't match (left hand would need to be complimented with right hand polarization) then a -20dB attenuation will be imposed. That helps kill unexpected signals.

And what does it all mean to me in terms of use in the RC wireless video hobby?

If your video Tx's antenna is Linear polarized and the Rx is Circular (either left or right), then the RF losses due to polarization alignment can be minimized. Theoretically, instead of a max -20dB loss, you would see a fraction of that. There is a penalty of -3dB when pairing a linear antenna with a circular polarized one. But, that is about as bad as it will get when it comes to the expected polarization issues. This combo has advantages and disadvantages, and as they say, YMMV.

Be sure you can trust your antenna vendor. Some have been known to claimed circular polarization out of wishful thinking rather than proven measurement.

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Thanks for the response, and let me try to clarify what I am looking for a little better.

My airborne tx is "linear polarized" (i think) in the vertical direction....i.e. antenna points "down" from under-belly mounting. On the rx it appears i should use a patch-style antenna instead of the whip that came with the rx. I am trying to decide what kind of patch to buy. Should it be "linear" polarized?...."circular" polarized?....if circular, should it be LHCP? or RHCP? or does it even matter that much or at all?

thx...

ob1

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Should it be "linear" polarized?...."circular" polarized?....if circular, should it be LHCP? or RHCP?
It can be linear or circular. The properties of linear vs polarized are as summarized above. LHCP and RHCP are meaningless if your Tx antenna is linear polarized and the patch is circular.

My fatherly advice (which will no doubt conflicts with other fatherly advice givers) is: If you fly in casual sport fashion during video sessions, then a good linear patch antenna will work great. Otherwise, spend more money and go with a quality circular patch.

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...Otherwise, spend more money and go with a quality circular patch.

OK....thx for the responses....you've convinced me to go "circular patch". You also indicated that I should beware of which vendors are "trusted".....so do you have any suggestions for which vendor and/or circular patch model I should aim for ?...thx

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