Electronics > Projects, Designs, and Technical Stuff
Digital FPV video for drone racing
dmills:
--- Quote from: Marco on January 20, 2019, 06:21:32 pm ---You'll still need a ~5 GHz synthesizer, already a boutique part to start with.
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Not really, use a crystal and multiplier chain instead of a synth and then do the selectivity at a lower frequency.
A chain of clippers and third harmonic filters is old school possibly but it usually has better phase noise then a synth, and the required filters can be printed onto the board at these frequencies, hell a nice quick snap or impatt diode or such and multiplying directly from 1.2GHz to 6 is not out of the question, I bet skyworks or microsemi or such have something that would work.
Once you have shifted the whole lot down to say 1GHz, the field opens way up in terms of how to do the selectivity.
Regards, Dan.
Marco:
--- Quote from: dmills on January 20, 2019, 05:26:35 pm ---But the channel you are trying to equalise is NOT LTI, because it is the FM channel you need to equalise and NOT the baseband, and there is a mess of bessel functions involved in mapping one to the other.
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It's been aeons since I had the mental faculties to do the math on this, but are you quite sure a constant multipath response won't approximately result in a linear response in the baseband as long as the carrier frequency is much higher than the bandwidth? The math in these course notes seems to suggest so, but as I said ... it's been aeons.
Intuitively if the multipath response caused nonlinear effects in baseband, baseband OFDM wouldn't work either.
The mapping of the two responses isn't really relevant, you measure it in baseband and you correct it in baseband.
hexahedron:
Ok, so I've been looking into inter-frame video compression standards, and I feel like I need some help. I've found http://www.openh264.org/ , an open source .h264 implementation, and after going to the github, I got a bit stuck. You see, I've taught myself everything I know about programming, but as tends to happen when you teach yourself, you end up with gaps in your knowledge. I don't know where the hell to start trying to learn how any of the code in the github repository works. How does one even start reverse engineering such an incredibly large project? Does anyone know if there is some paper or article that goes into the individual steps in order that h.264 goes through? I know I could just find some implementation for an fpga and copy/paste, but I actually want to know how it works.
EDIT: would it be worth it to just try an implement MPEG1/2?
Marco:
You don't, H.264 is not designed for high loss channels ... it's essentially useless to you.
Trying to do all this with a FPGA is a sure recipe for never succeeding IMO.
The output of the cheap receiver modules is actually not at baseband, you still need to downconvert it from 480 MHz before you can even start decoding it. Why not try to build a system which can sync the transmitter and receiver and sends an image as uncompressed PCM YUV before even worrying about compression?
hexahedron:
--- Quote from: Marco on January 20, 2019, 09:13:29 pm ---Trying to do all this with a FPGA is a sure recipe for never succeeding IMO.
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The more I read into compression standards, the more I have to agree with this sadly.
I guess the next logical step will be to purchase a beefy microcontroller of some sort. Any recommendations?
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