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| Digital FPV video for drone racing |
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| TheDane:
--- Quote from: IDEngineer on January 21, 2019, 08:38:06 pm --- This problem is almost always some pilot believing "It won't matter for just a quick second". They drop their transmitter power to "pit mode" (generally a couple of mW, whereas most racing is at 25mW these days), remove their transmitting antenna (never mind the SWR mismatch), etc. and "plug in for just a quick test". --- End quote --- EMC (Electromagnetic compatibility) is nothing new, and in fact something every designer/manufacturer must comply to if selling equipment, at least in Europe. When testing equipment, say naval emergency transmitters, it is paramount not to disturb the open air frequencies - unless you want a visit from the coast guard and their huge chopper. So, smart ingenious people (or poorer ;)) came up with a shielded box (Faraday cage) - and filtered inputs/outputs. https://www.google.com/search?q=emc+shield+box&source=lnms&tbm=isch&sa=X I know, organizers must have it and require its usage - but from the rules I have read it states that antennas must not be soldered on, so what is stopping the scene from utilizing these boxes, with screw on antenna cables + attenuation so the receiver input is not fried. A great way to test your equipment, without disturbing others. |
| StillTrying:
--- Quote from: dmills on January 21, 2019, 09:09:47 pm ---Any reason not to be thinking spread spectrum? ... Advantage is that unless someone has set the same spreading code as you a jammer will take out at most a few randomly scattered video lines instead of the whole thing. --- End quote --- Won't any other VTX have the same effect, especially when there's ~8 of them in use. |
| Marco:
--- Quote from: TheSteve on January 21, 2019, 09:06:46 pm ---I think you're in for a heck of challenge to successfully make a digital system that can replace the analog ones. --- End quote --- I'd just like to interject for a moment. What you're referring to as analog is in fact digital PCM + FM. Analogue is a corner case of digital modulation, the signal is generated by a DAC ... they just use a really weird encoding for legacy reasons. Once you cut the legacy NTSC out of the chain you can trivially change the resolution/refresh rate. An OV5460 can do VGA at 90fps and QVGA at 120 for instance. Even if you encode it as PCM, you have much more control over it. You're not reliant on some blackbox circuitry to synch to the NTSC signal for instance. If you have signal interference there is no reason to get confused, keep counting and the next pixel you get will be in exactly the right place. Who needs sync signals every line when you have crystals? You can throw a reference pulse in there every couple of ms and calculate the path response and correct for it, etc. |
| ogden:
--- Quote from: IDEngineer on January 22, 2019, 06:06:19 am --- --- Quote from: ogden on January 22, 2019, 03:29:49 am ---Pure BS. Let your son run 30fps progressive instead of 30fps interlaced (60Hz half-frames) and ask his opinion ;) Alternatively you can ask virtually any FPS/race gamer what is better for games: 30 FPS or 120 FPS. Kinda obvious answer, right? --- End quote --- We're talking about two different things. You're talking about refresh rate. I'm talking about signal path latency. --- End quote --- When you know latency of existing analog FPV radios, you know that there's nothing to improve. That's my point which I already provided BTW: --- Quote from: ogden on January 21, 2019, 07:50:56 pm ---If we want to beat analog TV transceiver latencyy using digital tech - we can't unless we increase frame rate. So, it shall be 120Hz or higher. Also whole frame buffering to compress/decompress is way too expensive waste of precious time. Analog TV transmits every scan line w/o buffering --- End quote --- Inter-frame delay time also shall be considered as latency - you want it or not. |
| TheDane:
--- Quote from: Marco on January 22, 2019, 10:29:06 am ---Who needs sync signals every line when you have crystals? You can throw a reference pulse in there every couple of ms and calculate the path response and correct for it, etc. --- End quote --- Crystals are NOT perfect, and will change frequency when subjected to g-changes (acceleration, deceleration, rotation). Ah relativity :box: An extensive subject, already looked into by TI, and not to be forgotten - it is not only reflection/multi-path/dobbler effect which affects system performance in this case. When designing a clock oscillator into a system, the impact of vibration is often overlooked. However, as demonstrated above, oscillators with similar specifications can xhibit vastly different behaviors when subject to vibration or shock, possibly resulting in the addition of tens of picoseconds of jitter and violation of design requirements. Very important when using mixers and/or multipliers - http://www.ti.com/lit/an/snaa296/snaa296.pdf Acceleration Sensitivity Characteristics of Quartz Crystal Oscillators - http://www.greenraytoday.com/beta1/wp-content/uploads/2017/02/AccSens.pdf |
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