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Old Feb 13, 2011, 11:22 PM
Derek_S is offline
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Videopilot
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Very cool idea. I will start looking for a dish, I am certain my dad has a few spares. It is amazing how disposable they have become over the last few years.

Lets say it has 23db gain, what can I expect as far as 'cone of vision'?
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Old Feb 14, 2011, 07:35 AM
IBCrazy is offline
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Engineer for Christ
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At 23db, you're lloking at 10-12 degrees. It's pretty narrow. However if you can fly a fairly straight line and pay attention to your azimuth you'll run out of battery well before you hit the end of your video range.

-Alex
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Old Feb 15, 2011, 12:53 AM
crash821 is offline
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Are you using a low pass filter between the Vtx and antenna with this setup or do you still get that clean of video without the filter. Also Alex, wasn't sure if you got my last few messages. Not sure why it won't let me send PMs and I'm not sure the link to email you is working all the time either. If you could, email me at sallis.chris@gmail.com so we can continue our discussion. Thanks again!
Old Feb 15, 2011, 05:55 AM
Flypoppa is offline
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Me a long time ago
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50 or 75 ohm?


OK I have got some memory wire and have started to bend.
I suddenly have to ask. If the equipment that we use is sometimes classed as CCTV and this is 75ohm.
But the other bits are 50ohm.
What cable and plugs should I be useing, 50ohm or 75ohm?
Old Feb 15, 2011, 06:30 AM
lovegroove is offline
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http://drone-pilot.blogspot.fr
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75ohm is only for the video out, at the tx and rx antennae it's 50ohm. Something like RG58 would work fine
Old Feb 15, 2011, 06:57 AM
Flypoppa is offline
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Me a long time ago
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Quote:
Originally Posted by lovegroove View Post
75ohm is only for the video out, at the tx and rx antennae it's 50ohm. Something like RG58 would work fine
Thanks for that.
Old Feb 15, 2011, 07:05 AM
lovegroove is offline
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I've found that it's just as cheap and much easier to buy something like this and just chop off the other connector that you don't need. That way you have the sma connector already mounted to the right sort of cable. Otherwise you have to get a special crimp tool for the sma connector and by the time you buy a sma plug and a bit of cable from Maplin it works out the same price.

http://cgi.ebay.co.uk/SMA-plug-UHF-j...item45f2cd0b6e
Old Feb 15, 2011, 06:17 PM
MarcAntonio is offline
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Speed Nut
Thank you IBCrazy for your great tips. Today I built my first homebrew antenna.
A CL for 2.4ghz.

I installed it on my cheapo (free) 10mw airwave transmitter from my trimersion headsets.

With the regular whip I would get grainy video after 1km max 1.2km.

I tested this and the graining begins at 2km , that's out of a 10 - 12mw tx.

I am sure I didn't do it perfectly because I have a 4-5mm gap between the feedpoint and ground, and It's working so well. I am still using a stock whip antenna on the receiver. I should try and use one of these on the RX unit as well and see what happens.
do you advise against using expanding foam to make a small dome to encapsulate the antenna?

Here is a pic of my little antenna:
Old Feb 16, 2011, 08:46 AM
Hugeone is offline
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My cloverleaf:
Old Feb 17, 2011, 04:53 AM
volto is offline
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Navigator
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Ok I am having a dense moment. Is the center conductor supposed to be shorted to the ground conductor with each element? Thats what it looks like is happening in the pictures, but that can't be right, can it?
Old Feb 17, 2011, 05:34 AM
Megafluffy is offline
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Quote:
Originally Posted by volto View Post
Ok I am having a dense moment. Is the center conductor supposed to be shorted to the ground conductor with each element? Thats what it looks like is happening in the pictures, but that can't be right, can it?
Its only a short for DC and low frequency.
For the high frequency we use on the video transmitters (900MHz to 5.8GHz), when built in the right dimensions, its a good match to the video transmitters output impedance of 50ohm (and the receivers input impedance).
So while the DC resistance is close to 0ohm, the high frequency impedance is close to 50ohm at the tuned frequency.


Megafluffy
Old Feb 17, 2011, 05:46 AM
jhoexp is offline
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Hi Alex, very useful post as always....
Started building two of them, one for a small multirotor and one for the ground station bridge/repeater to my fatshark, using 5.8 ghz video tx.

Any suggestion for this frequency, should i be very precise with this?
It's ok to use steel/iron wire instead of copper?
Feeding it directly to the the sma connectors (like hugeone did in the photo) can cause problems?

What's the best match on the receiver side (fastshark googles) for one of this on the air/ground? (keep in mind it must be small and light not to bother when you wear the googles)
Old Feb 17, 2011, 06:00 AM
mark hitchman is offline
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Zephyr 66" Blunt
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Quote:
Originally Posted by MarcAntonio View Post
Thank you IBCrazy for your great tips. Today I built my first homebrew antenna.
A CL for 2.4ghz.

I installed it on my cheapo (free) 10mw airwave transmitter from my trimersion headsets.

With the regular whip I would get grainy video after 1km max 1.2km.

I tested this and the graining begins at 2km , that's out of a 10 - 12mw tx.

I am sure I didn't do it perfectly because I have a 4-5mm gap between the feedpoint and ground, and It's working so well. I am still using a stock whip antenna on the receiver. I should try and use one of these on the RX unit as well and see what happens.
do you advise against using expanding foam to make a small dome to encapsulate the antenna?

Here is a pic of my little antenna:
That is an awesome result, will have to try one when my 2.4 ghz gear turns up, my be a bit draggy at 1 ghz.

Mark
Old Feb 17, 2011, 06:01 AM
mark hitchman is offline
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Zephyr 66" Blunt
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Quote:
Originally Posted by Hugeone View Post
My cloverleaf:
Excellent clear picture, makes it very easy to understand how they go together.

Thanks

Mark
Old Feb 17, 2011, 11:14 AM
volto is offline
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Navigator
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Thanks for clearing that up for me Megafluffy, makes sense now. I just built a vee and ground plane antenna, but this is next on the build list, I just had trouble wrapping my brain around the fact that this antenna is shorted together. =)


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