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Old Jul 12, 2012, 12:22 AM
USA, NY, Brooklyn
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Dual video TX?

Has anyone tried using 2 video transmitters (both with the same video input from one camera) at the same time, with identical antennas? Is it even worth a try or is it just a bad idea?
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Old Jul 12, 2012, 03:23 AM
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Two transmitters with identical antennas - so both on the same freq(?). I've always wondered about using 2 trasnmitters, one on say 2.4Ghz and one on say 1.2Ghz - then synchronizing the demodulated signals at the ground station. Just an idea.

With your idea KillerCut, I suspect results could be better if you stuck with 1 transmitter and invested in 2 receivers instead, each receiving the same freq - not in a diversity mode, but as seperate individual receive circuits, then synchronizing and joining up the 2 demodulated video signals. It would require a box of tricks to do properly (plug 2 video streams into the same monitor without any correction and you'll have a mess of a picture).

Another option, transmit 2 video streams on different freqs, and use a suitable diversity receiver to select one or other of the signals to use

If you want to try 2 transmitters with identical antennas, place one antenna on top of the fuselage and the other below the fuselage(?) ......... either way, the video signals are going to have to be combined on the ground.

....... there's a whole bunch of potential ways to run dual transmitter/dual receiver combinations. All have pros & cons, all add technical complexity and none is a perfect solution.

Worth trying - hell, why not. Just go read up a bit on combining video signals properly, because that's the main (but not only) technical complexity you'll need to deal with.
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Old Jul 12, 2012, 07:40 AM
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i was thinking of both vtx on the same frequency. If radio waves are anything like waves on the water or sound waves, when 2 waves join up they become bigger no? just wondering...
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Old Jul 12, 2012, 07:41 AM
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I think people already do use 2 vtx on different frequencies. I believe someone with a current or former long range record did that....
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Old Jul 12, 2012, 07:46 AM
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same frequency would just be a recipe for poor picture imho... you'd have signals reaching the antenna slightly out of phase and creating all sorts of problems

same frequency band, but different channels, yes... depending upon channel separation. Then you have two RX's, one on each channel. You then have a diversity unit hooked up which can pick the best picture between the two. Like this you can have two vTX's in different orientations and different positions, thus reducing the chance of entering a null or blocking the signal with part of the plane.

of course you need to split the video signal properly between the two tx's in the first place as well.
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Old Jul 12, 2012, 07:54 AM
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Radio waves are a bit like water, if they join up ( in phase) they will become bigger.
But remember there will also be times when they don't join up ( out of phase ) and in that situation the will cancel each other out.
And then there are all the times where they are at some degree of neither fully in or out of phase.
Its not the best way to improve your video signal.

You can have 2 video transmitters but they need to be on different frequencies (frequency diversity), its a lot like you and your mate flying FPV together at the same time on different channels. The drawback is you have to carry 2 video transmitters hence more weight, drag and power consumption.
With this method you still need 2 video receivers, one for each frequency.and then you would need a device to select which receiver to choose.
An RSSI based diversity selector is not suitable in this case as you are not comparing apple v apples, the freq's are different,
In this case you need a video quality comparator such as an Oracle or Eagle Eyes to select the best video signal.

As mentioned above, 2 video receivers with their own antennas (spacial diversity) is a much better way to go. You can select one of the antennas to be a high gain yagi or other exotic type. You still need a diversity comparator but you can use an RSSI based diversity or video quality comparator in this case.

Geoff
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Last edited by garris2; Jul 12, 2012 at 08:09 AM. Reason: Rusty must have been typing faster
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Old Jul 12, 2012, 08:53 AM
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I guess I forgot about the cancelling out part, lol. Very true. It would probably be more trouble than its worth to get the system to actually work the way I was thinking, you'd probably be better off just using a higher power vtx or booster... I'm already very familiar with diversity setups, I was just curious if it was the other way around, lol.
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Old Jul 12, 2012, 08:57 AM
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Sircana and Hugeone have experimented with it not sure if they flown it or if they have just done ground testing.
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Old Jul 12, 2012, 11:38 AM
OSUFPV - KF7VFT
Corvallis, OR
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I think he's talking about doing something like DIDO.

Yes, its possible to use constructive interference and your position to create a
stronger signal. Unfortunately, it's extremely difficult.

-Blues
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Old Jul 13, 2012, 12:26 AM
I LIKE WAFFLES....
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Sircana perfected it..
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Old Jul 13, 2012, 06:32 AM
Mums the word.
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Quote:
Originally Posted by SENTRY 62 View Post
Sircana perfected it..
He ment this link...

This link.
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Old Jul 13, 2012, 07:27 AM
I LIKE WAFFLES....
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LOL - yeah, that. LOL
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