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Author Topic: making a "Fox" for hunting plant theives  (Read 121906 times)

Posts: 2

« on: July 24, 2013, 02:20:28 PM »

I have a basic shack consisting of a VX7 and a few antennas. I will be adding to this collection as time and budget allows. With this meager beginning and your help I am hoping to stop an inconsiderate neighbor. I have recently lost three plants from my front yard in the past 2 weeks. They have been ground planted hydrangeas pulled out of the ground. Does anyone know of a simple and small fox that could be placed in the root ball that would send out a small but detectable signal? It would need to be waterproof and run for a number of days and a small battery. If anyone has any ideas, I would love to hear them. I will be adding a CCTV camera to the area, but being able to track the plant would be very helpful as well. If I actually catch the culprit, it would make a very amusing article. (Amateur Radio used to solve a criminal nuisance problem)
Thank you for your time.

Posts: 12773

« Reply #1 on: July 24, 2013, 02:58:42 PM »

It depends how complicated you want to get, what sort of range you need, and how large
the plants are.   (We have hydrangeas that are large enough to insert the tracker into a
hole in the trunk.  But more likely you are dealing with much smaller plants if the neighbors
are making off with them.)

A deluxe solution might be to use one of the APRS trackers sold for balloon launches and such -
they include a GPS unit to send their current position, and if there are within range of a digipeater
you can track the plant across the country.  Like this:

Another option would be an "FM Wireless Mic" operating in the FM broadcast band.  Here
is an example you can build:

You can build such a device for 2m just as easily, and adding crystal control isn't too difficult.
However, a simple crystal oscillator is probably easier (without the microphone circuit).  The
hard part is finding suitable crystals, but baud rate crystals that multiply up to 147.456 MHz
(fundamentals of 12.288 MHz, 8.192 MHz, 16.384 MHz, etc.) are stock items in most
electronic catalogs.  A 16 MHz crystal oscillating on the 9th overtone will hit the 2m band
with just one stage.  Such a stage can be powered by a 9V battery, or a small hearing-aid
size cell if one wants to get quite small.

To allow the battery to last longer, add a CMOS 555 timer chip that pulses the signal at a
low duty cycle.  This does make it more difficult to hunt, but can extend the useful life by
10X or more.  You'll have to see how long it takes your radio to register a signal and display
the signal strength, and make sure that your transmit pulses are at least that long (or look
for a local ham with better equipment that will help you.)

There are also some 433 MHz transmit chips available that would make it easier to build
something for that band - the higher the frequency, the smaller the antenna for the
same gain and/or directivity.

Suitable antennas can be built quite cheaply using WA5VJB's "Cheap  Yagi" methods here:

Posts: 12353

« Reply #2 on: July 27, 2013, 10:23:41 AM »

I had a problem with trash cans disappearing. I set a box in the bushes that contained an old siren, a  battery, and a micro-switch with a pull pin. A piece of thread went from the pull pin to the trash can. Next time someone grabbed the can the siren went off. I found the can laying there with the siren running and never had another missing can.  Grin

Posts: 78

« Reply #3 on: July 28, 2013, 05:17:43 AM »

Since you know its a neighbor why not get a picture of them for the police?  Go to your local sporting goods store and buy a trail camera.  These cameras are used for showing if deer are in a particular area.  They are not all that expensive and its pretty hard to lie when you have pictures of the person.

Posts: 12773

« Reply #4 on: July 31, 2013, 05:30:31 PM »

For shorter range work (for example, if you can walk around sniffing for the plant to
confirm that one your neighbor had planted came from your yard) there was a circuit
in Scientific American back around 1970 for a pulsed AM BC oscillator using a
single transistor.  This probably could be built for various ham bands as well, though
the frequency accuracy is likely to be rather loose.  (Especially while traveling
through a dog's digestive tract, as happened in one application - the timing of the
pulses served as an indicator of temperature variations.)

A similar oscillator could be made using a small crystal on HF:  it might not transmit for
very far, but could be detected from a few feet away.  DF in the conventional sense
might be more difficult ( a hand-held yagi isn't very practical at 10 MHz, but I make
hand-held 80m DF receivers using loop antennas) but you could simply sniff around
for maximum signal strength.

Unfortunately I don't have a specific circuit to point you to, but if you can give me
an idea of the expected distance over which you need to be able to hear the signal
then I can give it some thought - I've built a few such low level signal sources in
the past for testing receivers, etc.

Posts: 2639


« Reply #5 on: August 16, 2013, 10:57:21 AM »

Go with the camera.  Give the photo to the cops.  Pop a cold one and wait for results.

Posts: 74

« Reply #6 on: August 23, 2013, 04:21:58 PM »

Buy it at Walmart. save receipt. catch plant snatcher, return unit. 

Correct I dislike Walmart and I dislike China, almost as much as I dislike that @#)(*&^$$$R.


Posts: 12353

« Reply #7 on: August 23, 2013, 05:39:11 PM »

We're complaining that a thief is stealing plants so we're going to steal a camera from WalMart in order to get pictures for the police???   Grin

Posts: 791

« Reply #8 on: September 12, 2013, 06:07:49 PM »

Go with the camera.  Give the photo to the cops.  Pop a cold one and wait for results.

I would think that or a Claymore with a trip wire ought to do the trick Grin Or a exploding money pack with red dye that way there is no doubt on who did it Roll Eyes

Posts: 281

« Reply #9 on: December 09, 2013, 08:50:23 AM »

One thing to watch about the 'game' cameras. Make sure it has TRUE IR night vision. Most will say they have that, but make sure it is NOT visable to the human eye. Newer, more expensive ones will work.
How do I know? The crooks saw the flash and took the camera!!!!


Posts: 1368

« Reply #10 on: December 10, 2013, 10:50:47 AM »

A solar powered electric fence power supply with what looks like christmas lights on the bushes.

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
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