On Sun, 2004-01-11 at 13:46, Jack Smith wrote:
> You are going to have a couple major problems in this approach. Most
> importantly relates to bandwidth. You're proposing to implement a system
> that will have relatively narrow pulses (you didn't say what range
> resolution you require, but I'll assume is on the order of 10 meters.)  This
> means that you must measure the pulse timing within 30 ns. To do this, one
> would like a pulse that has a rise time of less than 30 ns, but let's say we
> can make it work with a 30ns pulse. That implies we need a 30MHz transmitted
> and received bandwidth, using the rule of thumb of 1/pulse width for
> bandwidth requirements.

I hadn't got to this yet, but what you say makes sense. The air traffic
example I gave operates in the microwave band so range resolution would
be much better.

> I'm familiar with the ITU's international radio bandplan, which almost all
> countries follow to some degree or another. You're in NZ, and I think you
> may well find that licensing a 30 MHz bandwidth pulse system in the 400 MHz
> band is somewhere between difficult and impossible. There are military
> radars that use this wide bandwidth in the 420-450 MHz band in the US (the
> band is shared amateur radio and military radiolocation) so perhaps that's
> your best bet for a wideband system.
>
> This also means that you are going to have to build all the equipment, as I
> can't think of a non-military pulse system operating in that frequency range
> anywhere in the world.

I'm getting less keen on building my first RF circuit in the UHF band.
FM seems far more predictable.

> But, there are other approaches that can be implemented in a narrow band
> system, say 30KHz bandwidth, using off-the-shelf FM transceivers. Let me
> describe one and you can judge whether it meets your requirements or not.
>
-snip-
>
> Jack Smith

Thanks Jack. I like the approach. I was referred to a number of COTS
components by another poster. This definitely seems like the way to go.

I am inclined to sideline the ranging problem for the moment and
concentrate on getting a transceiver pair up and running. If I can
simply get the status data in near-real time I'd be happy.

Rob

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body