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Old Apr 21, 2015, 04:09 PM
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Help!
Using a patch with a cloverleaf?

Hello,
Can I use a 900MHz patch antenna to receive video when I have a Left-Hand polarised 900MHz (cloverleaf) antenna transmitting video?
Thanks .
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Old Apr 21, 2015, 05:18 PM
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Yes; as long as the patch is also LHCP.
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Old Apr 21, 2015, 07:00 PM
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Wait...what?
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Quote:
Originally Posted by bigbird327 View Post
Yes; as long as the patch is also LHCP.
Not entirely true, if you use a linear patch antenna it has no polarization, it's linear.
There will be a 3db loss but other wise it will work fine.

Cheers,
Geoff
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Old Apr 22, 2015, 03:09 AM
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Can I get a circular polarised patch antenna?
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Old Apr 22, 2015, 03:23 AM
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How far does it go?
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yes, but a helical is better
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Old Apr 22, 2015, 10:40 AM
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Wait, so having circular TX and helical RX is better than having them both circular?
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Old Apr 22, 2015, 10:55 AM
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Quote:
Originally Posted by Im_not_Honeydew View Post
Wait, so having circular TX and helical RX is better than having them both circular?
Helical is Curcular polarization.
Having circular polarization on both ends is better than only one end, but still you can combine linear polarization with circular.
3db loss theoretically is half the range.
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Old Apr 22, 2015, 11:02 AM
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Quote:
Originally Posted by Im_not_Honeydew View Post
Wait, so having circular TX and helical RX is better than having them both circular?
Helical antennas are circularly polarized, just like your cloverleaf antenna is. The helical antennas typically have more gain than the patch antennas so you can get more range.

If you watch this video it will help clear up a lot of the antenna mystery:

FPV Antennas 101 - Polarization, Diversity & Gain Patterns (27 min 56 sec)
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Old Apr 22, 2015, 11:03 AM
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Quote:
Originally Posted by schumixmd View Post
Helical is Curcular polarization.
Having circular polarization on both ends is better than only one end, but still you can combine linear polarization with circular.
3db loss theoretically is half the range.
No, 3dB loss is half the power. 6dB loss is half the range.
The problem with mixing CP and linear antennas is that you lose all the multi-path rejection
benefits you normally get by combining CP antennas.
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Old Apr 22, 2015, 11:32 AM
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Originally Posted by Daemon View Post
No, 3dB loss is half the power. 6dB loss is half the range.
The problem with mixing CP and linear antennas is that you lose all the multi-path rejection
benefits you normally get by combining CP antennas.
Right Daemon, my mistake, thanks for correction.
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Old Apr 22, 2015, 01:03 PM
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Well, I've found a circular polarsied patch antenna, but it is 8dB compared to the 5dB of my current video RX cloverleaf. Is this increase worth the multipath rejection as Daemon said?
P.S. the video cleared some stuff up, thanks!
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Old Apr 22, 2015, 11:22 PM
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Cloverleaf should be 1.25dbic, not 5dbic.

In general, I find that if you mount a linear patch about 4" off the ground and use the stock antenna (not a cloverleaf) video works pretty well. However, using a cloverleaf on transmitter and receiver works even better in most cases.

-Alex
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Old Apr 23, 2015, 02:01 PM
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Is using a cloverleaf for video TX and helical for RX better than cloverleaf for both? Or, as you said in a previous post, a skew wheel for TX would work better than a cloverleaf when you're using a helical for RX?
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Old Apr 23, 2015, 10:12 PM
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Quote:
Originally Posted by Im_not_Honeydew View Post
Is using a cloverleaf for video TX and helical for RX better than cloverleaf for both? Or, as you said in a previous post, a skew wheel for TX would work better than a cloverleaf when you're using a helical for RX?
With a helical, any CP TX antenna will do. Skew wheel, cloverleaf, it really doesn't matter mch. just don't mix and match linear and circular. While it works, it is just not very efficient.

-Alex
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Old Apr 24, 2015, 12:16 PM
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Alright, I'll stick with my 900MHz cloverleaf for TX and attempt to make a 900MHz helical. Thanks guys!
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