Batboard

Hi we have a few quantar base stations connected with a wire line to a digitac comparator. we are looking for a way to triangulate the radios on the system and get gps locations of the transmitting radios via the receiving towers any idea.

What is the real question your trying to ask?

It has been proven for many eons that trying to rely on the phone company to not reroute the telco cable pairs is not going to happen. You spend hours in
setting up the time delays between the different locations and just when your done, the telco boys change the cable routing that your circuit took. This
throws off all that time you just got through spending trying to get all the delays to come out to where they needed to be. Why do you think so many of the
public safety agencies put in a microwave system.

I use to work for a cellular company, make that several over the years. We even had a problem with them changing the routing of T1 circuits. This would
mess up the coverage if you relied on the signal timing.

To triangulate the source of a signal, you need to know exactly where those receivers are. This process depends on the time of arrival of each of the
received signals at a central processor. If you change the length of the telephone line of one of those sites, it changes the time the received signal
gets to the processor. If you change a couple of the telephone lines, you fixed location as plotted by the processor can change drastically.

If your asking for a GPS location, then supply that information over the radio in each of the field units your trying to deal with. It is done all the time
every day in a good number of the radio systems around the country. The down side of this is that the employees that have this information being
supplied feel like they are being spied upon. So you have the political fall out of AVL (automatic vehicle location) information acting as a tattle tale to
where a vehicle is all the time. The use of this involves adding a box and a GPS antenna to the vehicle and sending a burst of data at the tail end of
each transmission.

The equipment can get expensive depending on what your trying to accomplish and the numbers of vehicles involved. It will work much better to use
a black box on the road rather than trying to install the electronics at each receiver point in your radio system. Plus you don't have the issue of the
telephone lines being changed by the telco all the time.

Jim

911-EMT wrote:Hi we have a few quantar base stations connected with a wire line to a digitac comparator. we are looking for a way to triangulate the radios on the system and get gps locations of the transmitting radios via the receiving towers any idea.

Good morning EMT - As Jim hinted, triangulation and gps are two different things, but there are products on the market that can do one or the other.

As it stands your current system would better suited for gps avl than triangulation. It's just a matter of researching the available avl products, and working up a budget for one. Talk to your tech services department. They may have a preferred vendor. The downside to mixing data over a voice channel is the data bursts themselves - they sound annoying. Some people can deal with it, some people can't. However, they work just fine. On the other hand, with the move towards narrowband and the advent of digital radios, it's possible to include the location information in the data overhead and never hear it in the voice payload. Again, talk to your tech services. They may already be working on it.

Triangulation is a rare bird and can get quite sophisticated. The technical issues, as Jim was pointing out, can be enormous, and he didn't even begin to address the computational fixed end equipment necessary to pull it off. It's not something you can roll your own unless you happen to have a few EMT's who were physicists in a former life. But, if you really want to pursue this, you should look at WinRadio, Doppler Systems, or similar products.

http://www.winradio.com/index.htm

http://www.dopsys.com/ser6000.htm

Pedantically speaking, if you are using arrival time differences at each of your receivers, you are doing multi-lateration and not triangulation. Non-pedantically, this means that you need 4 receivers to get a fix on a radio. The time differences for each pair of receivers gives a hyperbola of locations for the sending radio and you need three hyperbolae for a fix. R1-R2 gives 1 line, R1-R3 gives second line, R1-R4 gives third line. Any other combination gives a linear combination from the given set (because the geometry is fixed). In order to reduce the number of receivers you need to know exactly when the terminal transmitted the signal that you measured.

Agree with the other poster that any delay variation in the linking completely screws you up. Timing inaccuracy of 1microsecond is 300m.

GPS data messages from the radio are by far the best way in terms of reliability, accuracy and coverage.

If your intention is to set up a system whereby you can start to locate an illegal radio on your system, you would have much better luck purchasing an RDF (or ADF) setup. A Police service up in Northern Ontario had a problem with someone jamming their system and were able to track him/her down within a few days using an off the shelf RDF setup designed for marine use. However as the other poster said, if you are looking to use this to obtain the location of a legitimate system user (in place of GPS tracking) this wouldn't be a very good option as you cannot rely 100% on the results you get. The Canadian Coast Guard has triangulation services available providing your transmitting signal can be picked up by 3 or more receive sites. The few times I've utilized this service they weren't able to provide me with a location better than 1km accuracy.