radio-tx on a rotating platform:: will it work? - Page 1
Forum section: electronics / projects

author: 0db
author_rank: Frequent Contributor
timestamp: July 26, 2020, 01:12:23 pm
content: Yesterday I had the crazy idea of putting a radio transmitter on a rotating platform. This way, in my head, the transmission of data to the ground platform is completely decoupled.I mean the ground platfrom doesn't rotate, it should have a radio receiver and should just needs to provide power to the rotating platform via a rotating decoupled ring. This ring is good for providing power, but too noisy on data, because each electrical contact on the rotating ring does crawl, and this produces electrical noises!What I wonder is ... if the rotating platform does need to rotate at 6000 turns/min, will it produce any problem to the electromagnetic signal received on the ground platform?Supposing I will use Amplitude Modulation for transmitting information via a radio carrier wave. On the rotating platform the carrier wave will be around 600Mhz while the signal strength of the carrier wave will vary in proportion to that of the digital message signal being transmitted.Say, V1 for the "0" logic, and V2 for the "1" logic.Will it work? Or will I see any weird effect on the ground receiver due to the the rotation of the transmitter?Thanks

author: 0db
author_rank: Frequent Contributor
timestamp: July 27, 2020, 10:26:48 pm
content: I will also consider different modulation techniques and frequencies for the carrier.To choose the best.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: July 27, 2020, 11:34:17 pm
content: I have worked on such systems working at 1000 to 1500 rpm. I don't see any real problems with extending the speed up to your range. I agree that AM probably isn't the best modulation choice. you have a very well chosen and tuned antenna with no obstructions as your platform turns you will see large amplitude variations in your signal.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: July 28, 2020, 12:04:28 am
content: Use a ferrite transformer like VCR heads used. You can even get them as standard parts -- not to the same aspect, mind, but pot cores have the same shape. Downside, you only have the one potcore that's concentric, but that should be enough for a single transmitter!If this is VHF and up, you'll probably want to design the transformer with matching in mind. That is to say, the reactance of the leakage inductance, of a conventional split-bobbin ferrite transformer, may be too high for drop-in operation, and the ferrite may not do much of anything at those frequencies, either. You then might use an air-core double-tuned resonator -- the same thing without core, and with capacitors and coupling adjusted to give low insertion loss at the system impedance and frequency. It will serve as a bandpass filter of course.Tim

author: TheMG
author_rank: Frequent Contributor
timestamp: July 28, 2020, 12:55:54 am
content: For transferring data to and from a rotating part, the method of choice nowadays seems to be capacitive coupling. It's used in smaller industrial devices to things as large as medical CT xray machines. Data rates of 100Mbps or more can be achieved.In a nutshell, it's essentially an RF data transmission technique but without actually radiating a signal through an antenna, you're just capacitively coupling the signal from the rotating to the stationary part by proximity.The implementations I've seen use a couple of traces around the circumference of the spinning part, and a detector/receiver on the stationary part, just a millimeter or so above the traces. How exactly the data is modulated out to the capacitive traces and how they deal with the propagation delay on larger rotating parts, I'm not sure. Might be able to dig up a few patents and get some ideas.

author: wizard69
author_rank: Super Contributor
timestamp: July 29, 2020, 01:41:25 am
content: If you have your heart set on a radio solution realize that the FCC comes into play and could add a lot of complexity to a DIY project. So if you really want to do RF, make use of a validated RF solution that does the telemetry you need on an approved radio band. Using already engineered solutions will save you a lot of work.However I also have tp agree with others that looking at alternative communications systems may make sense. Somebody most likely already makes a coupling for what you want to do.