Mark, it sounds like you are describing CHIRP. A long time ago I use to
work with this in airborne RADARs. It was used in a side-looking RADAR on an
RF-4C. Secret `stuff' at the time... That would be one solution and a good
one. In anycase, Dominic is not going to be able to do this in current
digital `main-stream' technology for a 1ns resolution. He's going to have to
use analog with the PIC used for control, processing, driving a display,
and/or communicating with a host platform. Tjaart mentioned charging a cap
but that brings a whole new set of problems. I don't know if Dominic works
for a company with the design tools and the ability to manufacture products
in the 1+ GHZ range.

   If Dominic could provide more details about the target environment,
background `clutter', and why he needs 1ns resolution, maybe we can offer
more help.

BTW, I think you and I have `crossed paths' before. I live just north of you
in Portland and I created and operated the Northwest Amiga Group (NAG) BBS for
6 years. If so, please forgive my memory. I'm lousy with names but I never
forget eyes. I can almost hear Andy Warren saying; "See! If I was that old I
would'nt have any memory!". Just kidding Andy ;-)

   - Tom

At 10:08 PM 6/18/98 -0700, Mark G. Forbes wrote:
>[Dominic explains....]
>"Okay here is why I am looking to get a 1nanosecond clock pulse. My application
>is to measure the distance between 2 unknown points ( at most being 500-600
>yards
>apart) using a two-way (round trip) ranging principle based on point source
>radio
>systems. This is basically how I want it to work. Transceiver 1 transmits a
>signal(pulses), the signal is received at transceiver 2, and after a fixed
known
>delay , it is re-transmitted back to transceiver 1, is received by  transceiver
>1`s receiver and input to a ranging circuit. The ranging circuit measures
>the time
>difference between the original transmission time and the time of reception
>(less
>the known fixed delay) , which would be a direct measure of the two-way
distance
>when multiplied by the speed of light.This is the problem, the speed of light
>travels at 186,000 miles per second.That translates into roughly 98,208,000
feet
>per second. For an accurate measurement I would need an oscillator( I guess
>out of
>the question with a pic) that would supply my ranging circuit with a time
period
>that would translate into approximately 1nanosecond per foot. I would like
>to use
>a PIC to do all the conversions( time to feet and/or yards) and drive an LCD
>display. Any help will be greatly appreciated."
>
>Ok...everybody together now....."You're doing it all wrong!"
>
>That's a great idea, in principle, but as you've already observed,
>it's hard to put into practice because of the annoyingly fast rate
>that light moves about. Galileo had the same problem, *way* back when.
>
>This problem has already been solved, and you don't even need two radio
>transmitters to solve it. One will do.
>
>Create a radio signal of some reasonable frequency, say 902MHz. That's the
>ISM band in the US, a fairly un-regulated area to work in. Apply a modulating
>signal such that the carrrier frequency is swept up and down over a range.
>This is technology you can get off-the-shelf. Point your signal at the
>distant target, where you've installed an antenna, configured as a reflector.
>You don't actually *have* to use a reflecting antenna, but it'll make
>the signal discrimination a lot easier. At 900MHZ, these things don't have
>to be very large.
>
>The transmitting antenna sends out a signal, and it sweeps up in frequency. One
>round-trip-time later, the receiving antenna begins to pick up the signal
>that's been reflected back from the reflecting antenna at the other end. But
>right now, the transmitter is sending a signal that's higher in frequency
>than it was when it started, and so there's a difference in frequency between
>the transmitted and received signals. And that difference is proportional to
>the round-trip-time, and hence the distance. Using a mixing circuit, combine
>a little of the transmitter signal with the received signal. This will generate
>sum and difference signals, and you filter out the carrier frequency and the
>sum, and keep the difference. At zero distance, there's no difference between
>the two, and the difference frequency goes to zero (DC). As the distance
>increases, the difference frequency goes up. The sweep rate of the modulation
>provides the scale factor, and now all you have to sense is a signal that's
>somewhere in the audio range of frequencies. That's a *much* easier problem!
>
>Note that you can also determine speed this way; set the sweep to zero for a
>fixed frequency, and the difference tells you whether the target is moving
>or not, and how fast. Alternate sweeping with fixed frequency, and you can
>also tell which way it's going! This is some of the science behind radar guns.
>
>This works with light, too, and it's the principle behind things like laser
>rangefinders. Even cameras have things like this, these days, so it's not
>an expensive problem to solve.
>
>The ARRL handbook will have an assortment of useful information on RF design,
>which is where you need to be looking. A PIC could probably do the sweep
>control and the signal detection, but you've got other things to figure out
>that dwarf simple things like the control circuit.
>
>Mark G. Forbes, R & D Engineer  |  Acres Gaming, Inc.    (541) 766-2515
>KC7LZD                          |  815 NW 9th Street     (541) 753-7524 fax
>forbesm@peak.org                |  Corvallis, OR 97330
>http://www.peak.org/~forbesm
>mforbes@acresgaming.com
>
>"There has been an alarming increase in the number of things I know nothing
>about."
>---Anomalous
>
>