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Old Feb 28, 2012, 11:31 AM
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Joined Oct 2011
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Is this antenna setup wrong?

I'm getting real bad video reception with my best offer buy fox 700mw video system. Only about 100 feet before I lose everything. I have a turnigy 2.4ghz with frsky. Maybe my antenna setup is bad? Maybe I'm running the wrong channel? I did the testing in an urban area.

I am running a 1.2GHz High Gain Yagi Antenna, +12dBi on the Rx end.
http://www.dpcav.com/xcart/product.p...cat=272&page=1

and a 1.2GHz Antenna, "Big Stick" 7dBi on the Tx.
http://www.dpcav.com/xcart/product.p...cat=272&page=1

and a Low Pass Antenna Filter for 1.2GHz - 1.3GHz TX
http://www.dpcav.com/xcart/product.p...cat=272&page=1
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Old Feb 28, 2012, 11:59 AM
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Lakewood, Colorado
Joined Aug 2002
29,080 Posts
Yes, those are the wrong antennas. That high gain omni has only a 26 degree vertical beamwidth so you'll fly out of its beam as soon as the plane climbs or banks. Use a 2-3dB omni on the tx side. The yagi is high enough gain you'd need to keep it pointed at the plane at all times. It's good if you want to fly miles away but not useful for sport flying.
8dB patch is about the highest you want to go for sport flying and a good set of omnis at both ends will get you a couple miles with that vid tx.

ian
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Old Feb 28, 2012, 02:22 PM
OSUFPV - KF7VFT
Corvallis, OR
Joined Apr 2010
1,778 Posts
Quote:
Originally Posted by jb_bak View Post
I'm getting real bad video reception with my best offer buy fox 700mw video system. Maybe my antenna setup is bad?
Your setup shows a fundamental misunderstanding of antenna gain and radiation patterns.

Try watching this:
Antennas 101 - Polarization, Diversity & Gain Patterns (27 min 56 sec)


Blues
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Old Feb 29, 2012, 01:00 PM
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Ok got it! Thanks. Can anyone suggest a good set of omnis? Im still a bit confused why my big stick omni is bad for the tx side. My eagle ground station has tracking, so maybe i can find a good use for the yagi down the road.
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Old Feb 29, 2012, 02:28 PM
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Lakewood, Colorado
Joined Aug 2002
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Then apparently you didn't really get it.
"gain" means you take away some of the radiation in one or more directions and increase it
in one or more other directions. A high gain patch antenna decreases radiation from sides
and behind and focuses it in a narrow beam out front. A high gain omni (your Tx antenna)
decreases radiation from above and below, and focuses it in a narrow beam to all sides.
A 7dB omni has a 26 degree beam height which means if the plane flies level but up high,
then its beam is not pointed at your Rx. If the plane is far to the side when it banks, then the narrow beam
is not pointed at your Rx. The Tx antenna should be as low a gain as possible.. typically 2dB
so that the radiation goes in *almost* all directions equally. There will always be nulls
off the ends of the antenna (holes in the donut), but the fatter the donut shape of the radiation
pattern, the better.

ian
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