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Re: [Paparazzi-devel] digital video link anyone?


From: Gerard Toonstra
Subject: Re: [Paparazzi-devel] digital video link anyone?
Date: Sun, 12 May 2013 11:46:28 -0300

Yes, I posted on diydrones about this setup.

WiFi has a limitation of up to 55km because it needs to acknowledge receipt for 
packets and the max. waiting time is 800ns or so. 
The UBNT systems allow you to turn that off (ACK timeout), but then I don't 
know what the quality of the reception is going to be like.
Anyway, I don't think ranges beyond that are interesting anyway, unless you're 
in the mountains.

25W is huge. TBS did 80km (in the mountains!) with a 24dB grid antenna on the 
ground and 600mW video tx. 
There's a guy from Spain who worked on a perfect video link using circular 
polarization antennas. He mounted a dish antenna 
with helical and got 100km with 7 degree angle. As he also used attenuators, 
his theoretical range was 300km using 1W amps on the tx. 
A lot of the reliability and quality is determined by the antennas. Search for 
IBCrazy on Google to see a couple of interesting designs that
made large differences on the video quality and reliability for analog.

G>

On May 11, 2013, at 2:10 PM, Chris <address@hidden> wrote:

> Hi.
> Have you posted your efforts in DIYdrones? (if yes then i have seen your 
> setup, very very nice for me
> as my airplane can lift this setup easily)
> First of all i consider long range anything above 20km but usually above 40km.
> I haven't tried a digital link in actual flight only on the ground (1km) as a 
> test
> and i wasn't impressed with its performance vs price.
> The frame rate would vary drastically for a given power, i didn't used an 
> amplifier for 1km just the directional antennas as i needed to calculate how 
> far i can get with a given rf power.
> About the rotomotion system, one friend of mine has this setup from 
> rotomotion and it can do 15km easily but it consumes a lot of space and it is 
> rather heavy for an airplane, not to mention pricey.
> Now the second system from vfm store is one way which might be better but the 
> seller still hasen't answered a couple questions i had so i didn't bought it 
> yet.
> If it hasn't got the same picture quality as an analog PAL camera then i will 
> not buy it and test it.
> So far the best system i have used is an analog tx with video scrambler, 2 
> steerable antennas (a 5 element yagi, one on each wing) and a power amplifier 
> (address@hidden) mounted on a 3.1m span airplane.
> The only problem is that it is heavy as it needs large lipo batteries (only 
> the linear amp draws 10A so i need to turn on the vtx only when needed) and 
> that the antenna system is complicated.
> Finally i got hold of making high gain yagi  antennas perfectly matched but i 
> am searching for something simpler like this
> http://www.learningace.com/doc/2795149/2da44f2ac03124199b1d13881857375b/awpl_design-of-a-multidirectional-high-gain-compact-yagi-antenna
> Chris
> 




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