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Old Jun 18, 2013, 04:54 PM
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Antenna Mixing

hello everyone. I have flown fpv before with planes and quads. i took at break and now i am getting back into it. Im using a 900mhz 250mw video tx and i am mainly going to by flying about 1-2 miles away for me max. Got a twinstar 2 that will begin working on soon thats going to by my main aircraft. I was just wondering what type of antenna i should use. I know a little about them, but what i want to know is can i use a 900 mhz circular polarized antenna for the Rx and an Inverted V for the airplane? or is it better to use both circular antennas for both plane and rx, it just they seem kind of big to be sitting ontop of the airplane? thanks. I also have a 8dbi patch i had been using before with a 3dbi rubber duck on the airplane. thanks.
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Old Jun 18, 2013, 05:56 PM
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Originally Posted by navihawk View Post
hello everyone. I have flown fpv before with planes and quads. i took at break and now i am getting back into it. Im using a 900mhz 250mw video tx and i am mainly going to by flying about 1-2 miles away for me max. Got a twinstar 2 that will begin working on soon thats going to by my main aircraft. I was just wondering what type of antenna i should use. I know a little about them, but what i want to know is can i use a 900 mhz circular polarized antenna for the Rx and an Inverted V for the airplane? or is it better to use both circular antennas for both plane and rx, it just they seem kind of big to be sitting ontop of the airplane? thanks. I also have a 8dbi patch i had been using before with a 3dbi rubber duck on the airplane. thanks.
The Tx & Rx antenna types should match for the best result. Either two circular polarized or two linear. I run the 900 MHz with an Inverted V to a Biquad for longer range. The 5.8ghz gear are circular polarized, same with my 1280mhz stuff.
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Old Jun 19, 2013, 04:19 AM
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You can mix them with some loss. I use a inverted Vee on my Tx and a skew planner on the rx with 900mhz. I think 2 miles might be hard to get. I have 500mw and I dont think I have been 2 miles with the mix. I have a rca switch that I use to switch to a Biquad when the signal starts dropping.
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Old Jun 19, 2013, 12:17 PM
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Sorry i have a 500mw 900mhz tx, from all i have read that should be plenty of power for 2 miles. So i understand its best to use both same antennas. So i can use 2 inverted V one for the Tx and one for the Rx? or V doesnt work good on Rx?i figured my patch on the Rx and the V on the airplane would make a good combination?
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Old Jun 19, 2013, 12:50 PM
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hi

if you got linear ant on your plane,and circulair ant on your vrx
you last 3 db signal

linear works fine for 900 to 1300

2400 mhz and 5800 circulair works better

rob

but if your plane can have a circulair 900 to 1300 that,s works fine to they are big,that,s only problem
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Old Jun 19, 2013, 06:02 PM
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Originally Posted by navihawk View Post
Sorry i have a 500mw 900mhz tx, from all i have read that should be plenty of power for 2 miles. So i understand its best to use both same antennas. So i can use 2 inverted V one for the Tx and one for the Rx? or V doesnt work good on Rx?i figured my patch on the Rx and the V on the airplane would make a good combination?
Correct. Inverted Vee on the Tx and the patch for the Rx.
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Old Jun 19, 2013, 06:58 PM
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ok thanks a lot for the help guys
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Old Jun 19, 2013, 07:04 PM
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For whatever it's worth, the classic L-COM 8dB patch is not that great on 900Mhz.
The ground plane is just too small.
Inverted Vee on the plane and Biquad on the ground is a much better combo and
will reach out several miles.

As mentioned above, mixing linear and CP antennas will result in a straight up 3dB loss, which
is half the received power, or about 30% reduction in range which will make it hard
to get 2 miles on omnis alone.
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Old Jun 19, 2013, 07:40 PM
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ground plane? what does that mean? im thinking maybe switching to 1.3 those circular antennas are smaller.right?
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Old Apr 20, 2015, 10:45 AM
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When mixing linear and cp video antennas there is a 3 db loss, got it. However, might there be some other benefits to this setup? If I run a linear tx on 1.3 and a cp rx, might I have less dropouts to due a banking plane that puts the tx antenna out of polarisation with the rx antenna?

Thanks
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Old Apr 22, 2015, 02:20 PM
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Hmmm..interesting.... Im thinking, Gatling and Yagi on ground connected to Eagleeye and inverted V on plane.... Any thoughts? I have all the stuff, might worth testing
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Old Apr 22, 2015, 02:46 PM
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Well after testing I can report that linear on tx and circular on rx works fine. Range is reduced but its nice for close in flying because I dont have the polarization dropouts seen with linear linear. And I dont have to put my fragile and expensive and huge 1.3 cp antenna on small planes.
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Old Apr 22, 2015, 11:07 PM
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Hmmm..interesting.... Im thinking, Gatling and Yagi on ground connected to Eagleeye and inverted V on plane.... Any thoughts? I have all the stuff, might worth testing
Skip the Gatling unless you are putting circular on the airplane. If using linear either 2 yagis or two BiQuad antennas aimed a few degrees apart for good coverage will do well.

-Alex
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Old Apr 22, 2015, 11:08 PM
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Well after testing I can report that linear on tx and circular on rx works fine. Range is reduced but its nice for close in flying because I dont have the polarization dropouts seen with linear linear. And I dont have to put my fragile and expensive and huge 1.3 cp antenna on small planes.
The CP antenna shouldn't be fragile. Mine have been slammed into the Earth countless times. I just bend them back.

-Alex
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Old Apr 23, 2015, 03:06 AM
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Good to hear, I have bent mine back a few times and was worried it wouldn't take the continued abuse but now I will get back to slamming it into the ground

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The CP antenna shouldn't be fragile. Mine have been slammed into the Earth countless times. I just bend them back.

-Alex
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