Finding a cell phone via RF resonance?

Wouldn't a metal detector be easier?

James Arthur

Tried it. Although, the detector was a cheapie $50 from Radio Shack. The problem is that there's not a whole lot of metal in the phone. I tested the detector on the same model of phone, and the detector has to be really close (as in, I'd *see* it before the detector sensed it). Also, I don't need any of the ferrous-vs-non-ferrous discrimination that you find in some detectors.

I figured that searching for sympathetic resonance at a certain frequency would give me much better discrimination from other metal in the area and would allow me to scan larger chunks of the hillside. Ideally, I'd want something that could give me a 20'x20' area to look in.

- Joe

Wouldn't a simple grid search have been completed by now?

RL

Grid search is my recommendation. But you know, something tells me you didn't lose it there.

Call me psychic, but I get the feeling it will show up where you don't expect it. Now whether that occurs before or after you buy a new one....

If the phone's still alive, maybe some sort of simple RF detector (bug sniffer: whip, schottky, + op amp) would catch it talking to the cell tower.

Any attempt to ping it passively is going to be short in range and a big pain, technically.

James Arthur

Maker and model?

US football or UK soccer field? They're different sizes.

How long has it been running since the last charge? Anything over about 3 days is a lost cause.

My LIPO battery runs on an organic solvent, not juice.

Nope. The Q of the antenna and input diplexer are intentionally very low, to make the antenna useful over a wide bandwidth. If you're trying to build a passive transponder, it's going to need more Q than the phone can provide. You're also not going to find a grid dip meter that works at 900/1800MHz.

No.

Sorry, I can't help. I suggest you get a wide garden rake, and start dragging the "grassy area". If the vegetation isn't too deep, it should snag the phone. You could also try a metal rake, but that will take more passes. A metal detector should also work.

by this time... i would probably suggest to get a sniffer dog

You could have tried one of the services that used base station tringulation of the signal to locate a phone. Supposed to be good to within 25m in the USA if their publicity is to be believed. eg.

Once the battery is dead the thing is a fairly passive non-descript lump of metal that you might find with a metal detectors along with zillions of old coke cans and lost cutlery. At least no digging is required although you may need permission of the landowner to use a metal detector.

Very probably.

Regards, Martin Brown

Nope, that's UK thing. We don't restrict metal detectors in the US.

Cheers, James Arthur

How about a bunch of kids, and seed the field with a bag of candy?

Let it leak that there is a missing bribe, and you'll have thousands of politicians there in hours.

Well, if it's somebody else's property, it would probably be a Good Thing to get permission to go traipsing around in his yard. Maybe make a deal - any valuables you find, you'll split the proceeds 50-50. ;-)

Cheers! Rich

Good Grief! 20 by 20 feet? You could search that on your hands and knees in about an hour!

Have you tried retracing your steps?

Q: "Where were you when you lost it?" A: "If I knew that, it wouldn't be lost!" ;-)

Good Luck! Rich

Obviously, that will happen *after* a new one is bought, and he looks for something else...

Get a big lawn tractor and mow the lawn. When you hear a brief grinding noise followed by a "shwoomp" sound, you will have found where you left it. Seriously any technological attempt is going to cost far more than the phone is worth. If you lost it in a field it will either be damaged by rain or a mower or someone has found it already.

That reminds me of when i lost my previous cell phone. I could isolate the search area to 50 feet by 20 miles. I scanned it visually once, just in case the find might be easy. Then i bought a new phone instead.