rf distance measurement (2023 Update)

Reflections will be a big error source.

Complex modulation and phase-sensitive decoding is popular.

The speed of light is about 1nsec per foot, so you are talking about round trip times of 20nsec, 200nsec and 1usec.

It's easy enough to create a 1nsec wide pulse, but detecting it after it has been reflected from something 500 feet away trickier.

You've not been specific about your needs -- which may be as unconstrained as "how far is X from here?" Or, (in my case) where is X in the context of this arena?"

TI makes some kit that might fit your needs, depending on your actual specifics (IIRC, most of their solutions were geared towards optical sensing).

[note that there may be other (more reliable/cheaper) options depending on your goals]

Probably one uses a corner-cube retroreflector as a target, if you want good signal/noise. That's how this one is set up; give it a try!

Distance is likely to be over 500 feet.

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.

On a sunny day (Fri, 9 Sep 2022 00:08:39 -0700 (PDT)) it happened Ricky snipped-for-privacy@gmail.com wrote in snipped-for-privacy@googlegroups.com:

Why use RF? For 2 $ 50 centst you van get an ultrasonic distance measuring module on ebay I have several.

500 feet?

On a sunny day (Fri, 09 Sep 2022 07:38:18 -0700) it happened snipped-for-privacy@highlandsniptechnology.com wrote in snipped-for-privacy@4ax.com:

Its just about 150 meters... Just add a big piezo speaker / transducer to the output, have some here too.

Then all you need is a decent audio power IC or wind your own transformer and use some MOSFETS. You can beam that say 44 kHz audio, wave length is a few cm Done a lot of experimenting with ultra sound This is fun too: Top left and bottom right are the ebay distance meter modules, but I moved one of the transducers of each to the opposite side: But for long distance measurements I would use a laser, is also RF, just a bit more GHz,,

Ricky - the delay you mentioned is along the lines I've been thinking. Any suggestions on search terms? TACAN would be likely. What else?

Hul

Ricky snipped-for-privacy@gmail.com wrote:

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.

Hul

Anth> > Anyone know of any ICs designed for measureing distances with RF? I'm

Jan - did the requisite componets you mention answer your question "why rf?"?

Hul

Jan Panteltje snipped-for-privacy@yahoo.com wrote:

Loran, shoran, raydist, decca, and gee were RF location systems pre-GPS. And others. But they were long range nav systems.

Some like shoran were pulsed time-of-flight. The others were mostly sine wave hyperbolic, or hybrids.

Navigating boats to oil wells and rigs in the Gulf of Mexico used to be a big business. Those folks did some satellite nav systems pre-GPS; I helped them a little.

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.

Clifford Heath.

Clifford Heath wrote: ================

** The range of ultrasonic sound in air in measured in meters.

Your story seems completely fake.

...... Phil

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.

Hul

Anth> > Anth> > > > Anyone know of any ICs designed for measureing distances with RF? I'm

Clifford - looking at the laser tape measure sounds good. I'll give it a try.

Hul

Clifford Heath <no snipped-for-privacy@please.net wrote:

You are still top posting. Are you another one Jake Isks pseudonyms?

The Tellurometer approach lets you get away with a slower clock.

TTL works really badly at 500MHz.

ECLinPS offers counters that can be strung together more or less indefinitely to create a synchronous counter working at 500MHz.

I did a detailed design that depended on such a part back in 1995. The modern part is faster, but it's unlikely to make 1.3GHz if you string a bunch of them together.

You really do need to go to ECL if you want to ship fast clocks and signal around - you've got to treat your interconnects as terminated transmission lines.

Using the Tellurometer approach and measuring phase shifts is much easier.

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.

John