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Old Mar 13, 2008, 05:20 PM
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South Australia
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Modify 2.4ghz radio antenna for long range

I know most don't use 2.4ghz radios for long range FPV flights, but has anyone considered putting a higher gain directional antenna on the Tx? and maybe the Rx??

From what info I can find it appears the radios work on about 100mw (10mw in some countries, either way its not much!) transmit power. There shouldn't be any problem putting an 8 or 14db patch antenna on instead of the stock 3db one

Maybe even an amplifier??

Most of the wlan equipment should work fine I would imagine.

On another note. Pulling the back off my Futaba 7c 2.4ghz radio I see there is an antenna plug connected to the module board. It swivels, but I can't see how it unplugs.
Any ideas? It also looks like the same thing that is inside the receivers.

Any ideas on this one?

It would be interesting to see the range with a couple 5db antennas on the Rx and a 14db on the Tx.

Thoughts?
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Old Mar 13, 2008, 05:30 PM
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Daemon's Avatar
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Part 15 compliant devices are usually designed so that the
antenna is not meant to be removed easily. If it can be removed,
it's meant to have a proprietary connector to make it hard to
put some other type of antenna on it. This is part of
the FCC rules. That's why they came up with the weird
reverse polarity SMA connectors and such. As soon as
you replace the antenna, it's no longer FCC legal.

Yes you could use a high gain antenna on the Tx and/or Rx
but keeping them pointed at each other
will range from from difficult to impossible.

ian
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Old Mar 13, 2008, 05:33 PM
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Quote:
Originally Posted by wilsonj
Thoughts?
Of course possible, but not legal (on the TX side) as the maximum EIRP (which includes then antenna gain) would be exceeded. On the RX side it's not very interesting, as the improvement you might see in certain orientations of the plane would be a loss in other attitudes.
The connector in your TX is most likely a u.FL. You can remove it by pulling it out STRAIGHT. But be VERY careful, they're extremely fragile and only meant to withstand about 5 connection cycles.
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Old Mar 13, 2008, 05:57 PM
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Well I tried pulling on the plug a little harder and it just clipped off. I guess I was being a little too timid!

Now if I could get a pigtail with this connector.......

The alternative is to buy and sacrifice a cheap Rx for the antenna.

It should be available as a spare part I would think.
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Old Mar 13, 2008, 06:07 PM
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Ahh thanks for the replies.

I thought the legal side of this would come up. But really more than half of the video systems out there are illegal anyway. Not that that makes it right, but you get my point. Not to mention that many fly above the legal altitude for models, and I'm not even sure you are allowed to fly a remote vehicle out of eye sight. And so on........

In Australia we are allowed 4watts on 2.4ghz spread spectrum. But only 10mw non SS.

If the standard radio has an output of 100mw (~20db) then by adding a 14db patch antenna will ~34db, keeping it below the 36db allowed.

What are you allowed with the DMD 900mhz system? In the US?
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Old Mar 13, 2008, 06:07 PM
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Quote:
Originally Posted by wilsonj
Now if I could get a pigtail with this connector.......
You can find a LOT of u.FL to RP-SMA as that's common for Wifi. Takes a bit more time to find one to SMA, but possible: http://cgi.ebay.com/U-fl-to-SMA-wire...sid=p1638.m122
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Old Mar 13, 2008, 07:20 PM
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Thanks Kilrah, I might try one and report back. But it will be a few weeks I suspect.

Cheers
Jamie
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Old Mar 13, 2008, 07:45 PM
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Quote:
Originally Posted by Kilrah
You can find u.FL to RP-SMA as that's common for Wifi. Takes a bit more time to find one to SMA, but possible:
When my DX6 broke, I picked up a connector from these guys...

uFL 2 SMA
uFL 2 RPSMA
uFL to N (male)
uFL 2 RP-TNC (Linksys WRT-54g & few other Wifi)

I've heard of glider folks replacing their DX6 antennas with patch antennas. So anything is possible. I remember reading somewhere that going over a 5.5dBi antenna was kinda pointless. I'd have to dig it up.

Might want to read this thread to..

http://www.rcgroups.com/forums/showt...ght=range+6100
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Old Mar 13, 2008, 09:25 PM
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Wilson J,

The power limits on 2.4 GHZ are BS... Unless you are flying in downtown Sydney, it is just not going to matter. If you are out in the country, you have to have sensitive equipment and directional antennas to pick up a 2.4 GHZ video transmission more than a couple miles away.

Power limits were designed to reduce intereference to other users, so putting up a high power 2.4 ghz video system in the middle of a city would be irresponsible. But if you are flying your FPV plane out in the country, it wont bother anyone if you have high power... The hell with legality, its kind of like trying to enforce nudity laws in the outback, if you are out where no one can see you, only an idiot would say you can not tan naked wher no one can see you because its against the law . Its so easy for everyone to say " Its the law ", but those same people will exceed the speed limits in their cars every day, which has a much higher chance of actually hurting someone. I dont listen to self rigtheous people that spout the standard response without even thinking ....

That being said, You can get a 1000 mW 2.4 GHZ video transmitter from www.rangevideo.com I fly to 10 miles pretty easy with a standard 3 dB TX antenna. If you use good judgement, and fly in remote areas, it will never make an ouce of difference to anyone if you run 10 mW or 10000 mW

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Last edited by JettPilot; Mar 13, 2008 at 09:47 PM.
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Old Mar 14, 2008, 12:49 AM
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typicalaimster, thanks for the links. I'll do some more reading and research. Odd that 5.5db is the limit though.

JettPilot, funny enough I live in the outback. I am aware of the "self regulating" nature of the LIRP frequencies, and agree totally. Although I might have to re-think the nude sunbaking what with all the FPVs around!! hehe
Most people break the law in regards to video transmission anyway.

I have a 1 watt 2.4ghz video Tx. But I have recently gone to 2.4ghz radio, and so ordered a 900mhz 500mw video Tx with diversity Rx and patch antennas.

My objective is to try and fly from my place to my friends, which according to google earth is around 6 Km. Although this shouldn't be too much problem for the video the remote will be. I think 3km is about all I could hope for from it. Hence I am looking at a different antenna solution.
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Old Mar 14, 2008, 02:11 AM
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Quote:
Originally Posted by wilsonj
Most people break the law in regards to video transmission anyway.
Are you referring to Australian law? The equipment used and sold in the US is not illegal as far as I know.
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Old Mar 14, 2008, 02:23 AM
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yeah certainly in Australia anything over 10mw is illegal. But I thought that 1watt would be illegal in the US. ???
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Old Mar 14, 2008, 02:49 AM
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The actual transmission limit is measured in EIRP. EIRP is kind of like intensity - it's a combination of transmission power and antenna gain in the system. For example in the US, in the 2.4 GHz 'open' bands, a 1 W TX with a 6 dBi antenna sits around the EIRP legal upper limit. There's a lot more information on the subject, but in summary Australia (and some other countries) have tighter limits than the US in the 2.4 GHz band.
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Old Mar 14, 2008, 09:59 AM
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6 KM should be no problem at all for your system. Get an 8 dBI reciever patch for the 900 MHZ video receiver, and I would also highly suggest a 3 dBI rubber duck antenna for the 900 MHZ video TX, the short little antenna that comes with the 900 TX is useless, not even tuned for that band. If your plane is to small for the rubber duck at 900 mhz ( kind of big and heavy ) , I would make a vertical dipole out of music wire for the video TX.

For your 2.4 GHZ RC transmitter, buy a 14 dBI patch, mount it on the back of your RC transmitter, and just keep it pointed towards your airplane as you you fly, that will increase your 2.4 GHZ RC range by a huge amount if properly setup.

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Old Mar 14, 2008, 12:35 PM
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Quote:
Originally Posted by JettPilot
For your 2.4 GHZ RC transmitter, buy a 14 dBI patch, mount it on the back of your RC transmitter, and just keep it pointed towards your airplane as you you fly, that will increase your 2.4 GHZ RC range by a huge amount if properly setup.
Or just mount it on top like the glider guys did. I think it's been discussed here that you could probably go with a one way amp on the unit. Basically take a pigtail out of the DX6, run it through an amp, then out to the antenna of choice.
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