Long Range Wireless

[Kickin]

Hello.

I am planning a tracking system using GPS. It will be made up of several parts - a 'base station' consisting of a laptop or PC, will receive the signals from varios 'clients'. The client parts will each have a GPS module and some form of transmitter.

The base station will the continually get updated with peoples/cars positions, and plot them all on a map (this isnt a priority atm!)

The problem I am having is getting a suitable transmitter/receiver that will work up to a range of up to 40 miles (if base is static). The only thing I can think of is equiping each tracking unit with a mobile phone. When the base station phones, the mobile will automatically be 'picked up' and the current GPS data sent via audio.

Do you think this will be the only feasible method of communication? Something without the cost of hundreds of 10 second calls would be nice :-)

Thanks for any info :-)

[Dwayne]

Hello Kickin,

Kickin>>The problem I am having is getting a suitable transmitter/receiver that will work up to a range of up to 40 miles (if base is static). The only thing I can think of is equiping each tracking unit with a mobile phone. When the base station phones, the mobile will automatically be 'picked up' and the current GPS data sent via audio.<<

Ok... Lets look at the facts...

There will be NO WAY ANY RF signal will go 40 miles way in the VHF region (lets say above 50 MHZ). A 144 MHZ signal running 40 watts of power will go about 15 to 20 miles on the average. If nothing is inbetween them, it can go further...But don't count on it. 15 to 20 miles is EXTREMELY EXTREMELY good. Radio communication is one of my specialties.

Rule #1... VHF is LINE of SIGHT... if you cannot visually see the other person...you will start running into trouble. Thus,if you are within about 4 to 5 miles of each other, you may be able to communicate spottedly.

Rule #2....HF is NOT line of sight...But you have another problem... The antenna being long enough, and what time of day you are using it.

Basically said the answer is no... You must use some other method than Radio signal...OR use a Repeater to transfer the data. And using the Repeater is NOT a guarantee of 100 percent 40 mile range...

Using Cell phones, may be the SUREST way to receive GPS data on location, because of the number of Service repeaters. And they already have them set up! <g>. How you transmit that data is up to you...But the faster the transmit, the less reliable on the receiving end. And when going through Cell phones, I would suggest keeping your Baud at 1200 and below... preferably 300 or below. And if you could... about 45 or so. The slower buad rates will be easier to test and work with...until you have established positive and reliable communication.

Dwayne

Kickin >>Do you think this will be the only feasible method of communication? Something without the cost of hundreds of 10 second calls would be nice :-)
Thanks for any info :-)<<

You have some huge problems...

1. Line of sight.
2. Power of transmitter.
3. obsticles as you encounter them. (will kill your signal).
4. Antenna length for proper and max signal output.

Sometimes those 10 second calls are really nice....especially if they are reliable and the system is already set up for you...

Dwayne

[Kickin]

Thank you.

I think I will now be able to pull the project off when I get time, and a couple more $$'s

- Picking the phone up when it rings will be ok (check for speaker high - short out the 'green' button.)

- Putting the phone down will be ok (short out the 'end' button).

- Sending the data *may* be ok (replace the mic with fly leads), however, the mics are miniscule, so theres a big chance of me breaking it!


The only problem I see is the data itself. You mentioned using a low baud rate (outputting the data as text?). Would this be better than devising a 'morse code' style system, sending different length pulses - perhaps a short one to mean '1', and a long one to be a 'break'??

Thanks for your help

[Dwayne]

Hello Kickin,

Kickin>>The only problem I see is the data itself. You mentioned using a low baud rate (outputting the data as text?). Would this be better than devising a 'morse code' style system, sending different length pulses - perhaps a short one to mean '1', and a long one to be a 'break'??<<

This is all up to you...How you send your text is up to you...I prefer Morse... But hey...when you read 40 WPM in your head, its easy to decode <g>. IT also needs no special equipement like a PLL for different tones (like in RTTY). Dashs are 3 times the length of dots... space between words is equivalent to a dash. space between dots is a dot.

I have no experience with Cell Phone and PIC connectivity. But, if you want to use SMS, maybe someone like Ralph can help you... I believe he has much experience in Cell phone/PIC communication. I do not know how much data you are sending, but 40 WPM is approx 200 characters per min...(A word is considered to be 5 characters in length).

I doubt if I have helped you much, but maybe this will give you some ideas.

Dwayne

[Kickin]

Thanks again.

I think I will go with the text to start with, then try morse later - start with the simpler

I probably wont use SMS for a couple of reasons - firstly it will prbably require loads more work (lazy me ) and secondly, I would need to top-up every phone when it ran out of credit, rather than just the 1.

Thank you once again for your help

[scorpion]

check www.sierrawireless.com they might have something that you could use
-scorp

[Ioannis]

If I had such a project I would definetly use GSM devices, may be SMS message sending but prefferably GPRS that is now very cheep (at least in my country) about 15 Euros per month per 10Mb traffic.

Ioannis