Anyone know of any ICs designed for measureing distances with RF? I'm thinking in terms of 10 feet, 100 ft, and 500 feet with resolution to one foot. The basic method of one device emitting a signal and another echoeing it back would be attractive. Any recommendations?
Not if an active transponder retransmits the received signal with a fixed delay. That's how they measure distance in the TACAN system on airplanes. They use different frequencies which prevents an issue with echos.
Bill - the complex modulation & phase sensitive decoding along with multiple frequency direct are areas that would require a bit of study on my part. The 500mc clock required with the basic way with 2 transmiter/recievers is a problem too, probably an fpga. If some IC maker has packaged some portion of this approach the task might be simpler.
Anth> > Anyone know of any ICs designed for measureing distances with RF? I'm
A friend worked many years ago on an ultrasonic method for measuring the velocity of raindrop to look for windshear, microbursts, etc, for aviation. They used an ultrasonic transducer at the focus of a 2.5m dish (ex sat-coms) and got good results out to 6 kilometers.
Why can't the OP use the guts of (or chips from) a laser tape measure?
Or put a PA on one of the Infineon 24GHz radar chips?
I don't think the Decawave modules would get the required range.
Don't top post. It makes life difficult for your reader.
It's 500MHz and back in 1995 I was planning to buy one off the shelf (for about $100) which was based on a thinned-crystal oscillator.
There are a lots of faster options around today.
The whole point about the Tellurometer approach is that you don't need that kind of clock speed, but you do have to measure small phase differences pretty accurately, which isn't all that difficult. Twenty bit Sigma Delta A/D converters can be useful here.
is dead slow, but once you have used a phase-sensitive detector to convert the phase difference into a DC voltage you can measure it as slowly as you like. Ingenious people get the phase difference to reverse from time to time which lets you cancel out any DC offsets
Whatever you do is going to take a bit of study on your part. The more study you do, the more likely you are to come up with a n approach that can be made to work. Coming up with an approach that is likely to work well will take even more.
A field programmable gate array is a fairly heavyweight device. Less ambitious programmable logic devices should contain enough gates to do the job.
I quite liked the Philips CMOS Coolrunner parts, which they eventually sold to Xilinx, They drew a lot less current than the competition (unless you clocked a lot of the gates really fast).
Nobody here has come up with an off-the-shelf part yet - I've never heard of one, but that doesn't mean much.
Bill - the coolrunner is an attractive device, especially for a fundamently simple circuit as this. Unfortunantly it can't handle 500mc. If I remember correctly they are limited to somewhere between 100 & 200mc. The fpgas are, as you imply, a complex effert starting from scratch, but at least another tool would be added to one's "tool box". Can you - or anyone else - suggest an fpga that can handle 500mc and be in the $10, $20, $30 price range? What's really needed is an 8 bit counter with a latch that can handle 500mc, ala the
20 pin ttl chips.
Anth> > Anth> > > > Anyone know of any ICs designed for measureing distances with RF? I'm
Yes. At 20kHz the attenuation of sound by the atmosphere will be around
0.5dB/m (depending on temperature and humidity), so at 6km with a total path length of 12km the absorption will be around 6000dB. At 60m the attenuation would be 60dB there and back plus the losses due to imperfect focusing and most of the signal from each raindrop being scattered in all directions. Higher frequencies would give a tighter beam but even more attenuation.