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

[nisma]

 

You could embedded data inside the analog video too, named closed caption encoder/decoder.

Either as low speed CC or higher speed Teletext or any other type of formatting, even uart.

http://en.wikipedia.org/wiki/Teletext

You just need a circuit (pic microchip as example) that extract the infos. This is for Analog video.

 

Digital video is annother issue, you need a analog video sender on the right UHF band that are covered by

DVB-T reception range and where on you´r country this band is not in use. Now, usa a cheap QPSK modem

in order to send the digital TT channel or analog video channel using a pal/ntsc encoder and trasmit the resulting

output from the modem with the analog video sender.  This for unscrambled video, scrambled video is a bit tricky

and for such, probably it´s easyer using a FPGA that does the scrambling and the QPSK encoding of the video signal.

On the Net there is a reference design using Xilinx that output the data at 30Mhz with analog upconverter in the range of 1.2.. Ghz

suitable for a DVB-S receiver. 

http://www.videocashonly.com/images/large/35421_001_LRG.jpg , the Modulator is the QPSK modem, the combiner is the upconverter or

old analog UHF video sender, that used for 30mt and equipped then with a 10W amplifier as example in order to have enought power.

 

On the other side, this er all commercial off the shelf systems even for uav/observations, that doing this cheaply, but this require

goverment licence or special licence grand in order to buy this type of setup here in EU, for export, i think, you could buy it.

 

Gesendet: Samstag, 11. Mai 2013 um 19:10 Uhr
Von: Chris <address@hidden>
An: address@hidden
Betreff: Re: [Paparazzi-devel] digital video link anyone?

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



On 05/11/2013 07:00 PM, address@hidden wrote:
> Rotomotion uses a board similar to that. They also have a full-blown hub
> and wifi tx onboard and these are on gasser choppers.
>
> How far did you go with digital video and what do you consider long range?
>
> I worked on a setup and ground decoder to minimize latency. Unfortunately
> the wing loading turned out to be unfavourable,
> so it never flew very far, only about 100 meters. I was working with an
> arecont IP cam, a 3-pos "CyberData POS router board" powered by 5V,
> sparkfun ethernet breakout board (W5100) and Ubiquiti Long Range wifi
> modules. The UBNT PicoStation can be taken apart to keep weight
> down. I was using a Circular Wireless SPW antenna with Luxul CP 11dBi
> antenna. I have not been able to find reasonable alternatives for
> wifi that allows transmission of both video and custom data on the same
> link. So if you know of any, would be happy to hear about it.
>
> The W5100 chip is quite crappy to write data to. Every byte of data
> requires the transfer of 4 bytes in total over SPI.
>
> Rgds,
>
> Gerard


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