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Digital FPV video for drone racing

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Marco:

--- Quote from: radar_macgyver on January 20, 2019, 04:36:29 pm ---OT, but have you done any tests on that part yet?

--- End quote ---
Nah, just did a quick search for integrated receivers with synthesizer and mixer from the usual suspect and that's what was out there.

Marco:

--- Quote from: dmills on January 20, 2019, 04:41:07 pm ---I still think your receivers are the low hanging fruit, and I would absolutely start with some serious spatial and polarisation diversity probably with a pilot tone on the audio channel from the transmitter that my processing can use to assess quality. A few 20M or so cat 6 cables to carry the baseband back from the receivers and to carry power to the receivers, some processing magic (Fast ADCs, fpga with some sdram, video DAC or HDMI output) to dynamically equalise the path delays, and an alpha blend to combine the video signals based on signal quality indications, job done.

--- End quote ---
I don't think the race organizers will take kindly to the mess.

You don't need multiple receivers to equalize a channel, you just need the impulse response.

ogden:

--- Quote from: Marco on January 20, 2019, 04:00:23 pm ---They don't care if something else is transmitting on the band, they'll just try to shout over it ... since your transmitter is close to your receiver that's a shouting match you usually win.

--- End quote ---

Why would anyone shall [digitally] transmit on frequencies allocated for analog video! There's always option to transmit on legal WiFi channel and it is even advised to do so.

dmills:

--- Quote from: Marco on January 20, 2019, 04:52:32 pm ---I don't think the race organizers will take kindly to the mess.
You don't need multiple receivers to equalize a channel, you just need the impulse response.

--- End quote ---
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.
The impulse response only helps to the extent the transmission channel is linear and noise free which yours is not.

That TI part is in some ways overkill, if you make the first IF reasonably high (500Mhz - 1GHz??) then you don't need an I/Q mixer, because you can use front end filtering to get your image rejection, particularly if you use a high side LO.
Make the first downconverter LO fixed so you can use a multiplier from a good quality low phase noise rock, rather then a VCO and do all the selectivity work at the first IF. Minicircuits probably have a diode ring mixer that would work for this (Remember to terminate the IF power with a diplexer if you want good IMD3), and I bet one of the usual suspects have mmics for providing the considerable LO power needed by a high level mixer.

As to the organisers, you might be surprised, especially if you could offer them say everyone's baseband to put up on a big screen for the audience?  That TI chip has the IF bandwidth to be able to bring a dozen 30Mhz wide FM signals (FM occupied bandwidth is always much wider then baseband for obvious reasons) down to where you can decode them SDR style and having all the FPV video to stuff into a switcher and then onto a big screen might be a very attractive offering, more so if you can also offer all the teams better realtime video then they have from their own kit.

Half a dozen small boxes on short photographic tripods scattered around the course with cat 6 back to a little card cage with the baseband processing in it, then a BNC to each team and a bundle to the organisers?

Just a thought.

Regards, Dan.

Marco:

--- Quote from: dmills on January 20, 2019, 05:26:35 pm ---That TI part is in some ways overkill

--- End quote ---

Of course it's overkill, but everything at that frequency is boutique or completely application specific. Functionality and price have only a tenuous connection, you don't pay much more for the integration and it makes your life a little easier. There's not a lot of integrated solutions AFAICS.

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