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### Hollywood tracker beacon?

Posted: Fri Dec 13, 2002 5:01 pm
Would it be plausable, as seen in movies, to have a mobile transmitter and reciever combo, where when the distance between the two is increased, the pitch deepens on the reciever's speaker, and maybe even a few calculations and a distance displayed on a few 7 segment LEDs? Hopefully this system would work within few hundred meters, and be accurate within 2 meters or so. Anybody have any insight as to how to accomplish this without any GPS involved? Thanks!

### Re: Hollywood tracker beacon?

Posted: Fri Dec 13, 2002 5:24 pm
Think a little about doppler effect. How the police track your speed. They apply a simple physics formula with a pic adn VIOLA!!<p>Think about that one.....

### Re: Hollywood tracker beacon?

Posted: Fri Dec 13, 2002 5:34 pm
But would that work if both transmitter and reciever were standing still? Sorry, Gr. 10 in Gr. 11 Math here, no physics yet.<p>By the way, surprisingly fast reply!

### Re: Hollywood tracker beacon?

Posted: Fri Dec 13, 2002 10:20 pm
It wouldn't matter if they were moving at all. Go to www.howstuffworks.com and look at radar. That might help. In the mean time, i will look for some stuff.

### Re: Hollywood tracker beacon?

Posted: Sat Dec 14, 2002 10:59 am
I was imagining something a bit less complicated than tracking something using radar. The object I was hoping to track was, well, here's an example: finding your luggage at the airport. Beacon would be inside the luggage, and you could just walk straight towards it. I don't think you could track it with radar, because you'd have to know which one was yours in the frist place (as far as I know.)<p>I just remembered that there are real beacons like the one I've suggested. Avalanche beacons are small devices that skiers and climbers wear in case of an avalanche. I don't know what triggers them (user, or shock) but then the team looking for you can walk across the ground forming a grid pattern and find the spot at which the most LEDs are lit. Ours would probably need to be a bit higher powered, but I doubt too too much, as the snow must cause large amounts of interference and insulation for the signal.

### Re: Hollywood tracker beacon?

Posted: Sat Dec 14, 2002 2:24 pm
The avalanche beacons probably work on amplitude, the closer to the transmitter, the larger the amplitude. A receiver with a ferrite antenna will be directional, so you can determine within 180 degrees the direction to the transmitter. An amplitude display will tell if you are going toward or away from the transmitter.

### Re: Hollywood tracker beacon?

Posted: Sun Dec 15, 2002 8:39 pm
There is probably already a system that works like this, but I'm not aware of it:<p>If you and your target each have a transmitter and receiver, then you can initiate a pulse, and if the target receives it, it immediately sends one back. Since the propagation velocity of radio waves is known (~3*10^8 meters/sec), then if you know the turnaround delay of each transceiver (or use a PLL to eliminate it), you could calculate distance between the two transceivers from the frequency of the pulses that are being relayed back and forth. Transmitting a really short, fast risetime pulse requires a lot of bandwidth, so I doubt that this would be practical over short distances,because the rep rate would be too high. You could probably use fixed frequency sine wave modulation and measure phase difference, allowing the use of lower frequencies. At short distances, you need high frequency modulation to get good phase resolution, but phase becomes ambiguous if the phase shift is more than 360 degrees, so you would probably have to combine several modulation frequencies to resolve the ambiguities.<p>One of you forum trolls must know of some equipment that already does this - surveying equipment, maybe?<p>Ron<p>[ December 15, 2002: Message edited by: RonH ]</p>

### Re: Hollywood tracker beacon?

Posted: Tue Dec 17, 2002 3:54 pm
How 'bout this- The "reciever" transmits on one freq. and the "beacon" returns the signal on another freq. For distance, calculate the delay, less the known delays in the devices, against 300000000m/s.

### Re: Hollywood tracker beacon?

Posted: Tue Dec 17, 2002 6:13 pm
A bit more on avalanche beacons can be found here:http://www.couloirmag.com/gear/reviews/ ... 99.htm<p>I think that the beeping reciever you describe from the movies would probably work like this: The transmitter would be a continuous wave TX at a relatively low frequency of 450khz (from article above) and probably AM. The signal strength would decrease as distance increases. The reciever would measure the signal strength and apply that output to an oscillator circuit to make the ping. The beep most likely would not be the radio signal itself.<p>This is not unlike the cat tracking transmitter suggested earlier (except this would be non directional). Be aware that putting it in a suitcase would violate FAA law because you are prohibited from operating any type of transmitter onboard an aircraft. Putting it on a car would give you some advance warning when it is coming close to home.

### Re: Hollywood tracker beacon?

Posted: Wed Dec 18, 2002 7:32 am
A more advanced tracking device would sit in a low power mode and just be a receiver until a modulated signal is received and then respond with a know signal/tone/data. This would reduce power draw on the tracking device and also not violate FCC regs as it would not be a transmitter unless pinged.