Distance measuring

Looking for a method to measure distance. Need to measure the distance from 75 to about 600 feet. Thinking about using a couple sets of the cheap RF modules. Put a rec. and tran. together at each end. Send a very short burst of RF and have the R. trigger the T. direct. Then repeat at the other end in a continuous cycle. If I can get this to happen, I can then divide this pulses rate down to a reasonably easy time signal to process. One end will be stationary and the other end will be continuously moving. Hope this makes sense. — My question is what modules would work best. All I need is a fast response to turn on the RF for about 100 ns, and then have the far R to detect the signal and trigger its T. Anyone have suggestions on which modules you have used, or suggestions for me to try? Anyone have an alternative or simpler method for this project? Thanks.

http://www.instructables.com/id/Distance-measurement-with-radio-waves/

Hey Magician , thanks much for that lead. They are looking at almost the same problems I am. A lot of good ideas to follow up on. Not quite 100% of my questions, but good. My biggest question is what are the best modules for the price that will do the job.

I'd try the cheap ones, like https://www.sparkfun.com/products/10532 The problem I can see, is variation in amplitude of RF with distance would affect round trip time. Not ready to estimate how big error it may cause.

FM module would be nice to try, but unfortunately I can't find any on a market. Digital RFM12 and RFM22 seems to me have no direct correlation between time of arriving RF and time when it shows up at outputs, as there is internal shift logic, and amount of delay time it introduces not reflected in documentation. May works over big numbers of oversampling.

Analog module I linked above also could benefit using oversampling, statistical processing, to get down range error less than 0.3 metr.

I'm also thinking to build a mixer (low price) , that can create bended pipe for RF, receiving 433, than mixing up with 118 to get back 315. Far end would not have a delay at all in this case, just traveling time

You lost me on your comment of amplitude effecting time. Are you thinking RF speed, or reaction time in the receiver? Yes I expect there to be some variation in the time from receive to transmit, however by counting to 1024, or whatever, there would be plenty of time averaging to minimize that variable. At this time I am thinking about using straight CW type of signals, without using any modulation.

No ideas or help on your bent pipe project.

Are you thinking RF speed, or reaction time in the receiver?

Receiver, they build around super regenerative type.

Yes I expect there to be some variation in the time from receive to transmit, however by counting to 1024, or whatever, there would be plenty of time averaging to minimize that variable.

The problem with cheap receiver that error via AM is correlated to distance, and consequently averaging can’t cure. Though, a lot would depends on your expectation of the accuracy.

At this time I am thinking about using straight CW type of signals, without using any modulation.

In order to calculate a propagation time, you have to switch on/off CW, and this is a modulation, 1-bit, simplest form.

No ideas or help on your bent pipe project.

They call “bend pipe” when RF system consist of receiver antenna, mixer + amplifier , and transmitter antenna. So basicaly RF fly in, make U-turn (180 degree - bend pipe) and fly back to origin.