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Author Topic: RF hide and seek  (Read 829 times)

bkenobi

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RF hide and seek
« on: October 02, 2017, 08:42:30 PM »

This is an odd one.  I have a humidity sensor for a safe that is in 2 parts. There is a main unit that sits outside and displays outside temperature and humidity and a second remote unit that gets put inside to transmit the temperature and humidity to the main unit. I was testing things and somehow misplaced the remote unit. It's still within range of the main display, but I have no idea how to locate it.

Anyone have any suggestions short of going through everything in my basement? I was thinking there has to be a way to use an RF receiver and a directional antenna hooked to an Arduino or a PC. I also have one of those USB variable frequency radio cards that I ran with SDR Sharp a while back.

 B:(
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dhouston

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Re: RF hide and seek
« Reply #1 on: October 03, 2017, 06:55:49 AM »

You need to know the frequency and then have a highly directional antenna and a narrowly tuned RF receiver.
Most of these devices use 433.92MHz. You could build a yagi antenna and put it inside a metal guidewave like a cantenna but you would then need help carrying it around given the diameter needed for this frequency.
http://www.yankeecontainers.com/c/small-steel-drum/
Searching through the basement might be simpler.
« Last Edit: October 03, 2017, 07:30:46 AM by dhouston »
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bkenobi

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Re: RF hide and seek
« Reply #2 on: October 03, 2017, 12:20:14 PM »

LOL, that would be awesome to ask my wife to help carry.  Bet she'd say no.   ;D

I built a cantenna out of a soup can and a yagi/cantenna out of a Pringles can in the past for war driving.  It was fun in WiFi's infancy, but I don't think the same can would work here (2.4GHz <> 433.92MHz).  It's probably easier to look close than try to us RF to track it down.
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bkenobi

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Re: RF hide and seek
« Reply #3 on: October 03, 2017, 12:28:15 PM »

I just need to build a fox hunt antenna and I'll be set!

http://open-circuit.co.uk/wp/wb-yagi/

The whole sensor is only $20, so I'm not really going to spend $50 and hours of effort in finding it.   rofl
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dhouston

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Re: RF hide and seek
« Reply #4 on: October 03, 2017, 01:35:04 PM »

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bkenobi

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Re: RF hide and seek
« Reply #5 on: October 03, 2017, 05:52:08 PM »

Is it possible to use a portion of a faraday cage to make a sort of wave guide?  I'm thinking I could take a working antenna (even a simple whip) and taking a sheet of "cage" and wrapping it 3/4 of the way around.  I'm envisioning a pop or soup can with one of those twisted copper coil antennas stuck inside.  Heck, I've seen printable guides for wifi routers that you cut out and glued aluminum foil to.  I expect zero amplification but was thinking if it blocked the signal directionally, I could narrow down which pile to look in. rofl

Here's that printable one:
http://www.freeantennas.com/projects/template2/
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dhouston

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Re: RF hide and seek
« Reply #6 on: October 03, 2017, 06:45:30 PM »

If you have everything needed, it's probably worth a try.
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bkenobi

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Re: RF hide and seek
« Reply #7 on: October 04, 2017, 12:27:39 AM »

When I looked around this evening, I found the sensor exactly where it was originally put.  But, I cleared everything out of that location in an initial search.  I think gremlins were involved.  Either way I found it.  I still think an RF detector would be fun to play with so I am going to put it on my to do list.
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BackAgain

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Re: RF hide and seek
« Reply #8 on: October 04, 2017, 06:53:11 AM »

^^  I could get in to a whole bit about 'Membrane Theory' and how things move between layers (they're there one minute, gone the next, then reappear), but that may not be for this board.  I can't think of another reason why we can look at a spot and NOT see something we know we put there, look away for a few seconds, then look back and see it.


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bkenobi

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Re: RF hide and seek
« Reply #9 on: October 04, 2017, 10:29:31 AM »

In this case, I moved my rifles to empty the cabinet.  Nothing inside, completely empty.  I put them back and a day or two later the sensor was there sitting on top of the gun socks between all of the rifles.  IOW, it was on TOP of the stuff I removed.  I need to call in Mulder and Scully!
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dave w

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Re: RF hide and seek
« Reply #10 on: October 04, 2017, 05:59:26 PM »

^^  I could get in to a whole bit about 'Membrane Theory' and how things move between layers (they're there one minute, gone the next, then reappear), but that may not be for this board.  I can't think of another reason why we can look at a spot and NOT see something we know we put there, look away for a few seconds, then look back and see it.
I would be interested in this. Up until now I thought this was "Oldtimers", demons, or my tinfoil hat was leaking. 
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BackAgain

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Re: RF hide and seek
« Reply #11 on: October 04, 2017, 06:14:58 PM »

Well, I can't get into a whole thing about it because I ain't that smart.  Something I saw on one of those science documentaries years back dealing with alternate dimensions and realities, similar to string theory.  Made more sense to me than some other things.

My simplified version:  You lay a coin on top of a piece of paper.  You turn away and someone lays another sheet of paper on top of the coin.  When you turn back, you can't see the coin even though  it's still there, right where you placed it.  You turn away, they remove the top sheet of paper, you turn back and there's the coin.  A variation is that someone places a different coin on top of the second sheet of paper.  You're stunned to see that the nickle you placed face up is now face down, which makes you wonder what you did.


The theory is that all things 'move' between membranes (dimensions) which might account for the often confusing now you see it, now you don't phenomenon of losing things that are right in front of you.



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dave w

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Re: RF hide and seek
« Reply #12 on: October 05, 2017, 07:55:17 PM »


now you see it, now you don't phenomenon of losing things that are right in front of you.
Yeah. Been doing that a lot lately.
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