metal dector for barbed wire fences

On a sunny day (Sun, 17 Jun 2012 08:05:44 +0000 (UTC)) it happened Hul Tytus wrote in :

Whuy not reverse the problem, and put some RF one the fence? Then a small directional dipole or loop, or ferrite rod can pick it up?

915Mhz (ISM band if in the americas) 13" wavelength,

else yeah you'd need to use GHz signals, what's called RADAR

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Hul Tytus wrote in news:jrk34o$cj8$ snipped-for-privacy@reader1.panix.com:

helicopters have the same problem with power lines. AFAIK,they don't have any solution yet.

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nce

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I 'think' the military already has a solution. Especially for UAV's in urban areas. At least, they must, or else they would have used my sensors which can easily 'vector' AC mains from up to 100 feet away that combined with flight control and you get avoidance.It is my understanding they have a solution.

On a sunny day (Sun, 17 Jun 2012 09:29:08 -0500) it happened Jim Yanik wrote in :

Many power lines these days carry internet on RF carriers. Should be very easy to detect. Usenet patent 123123123 You have seen it here, prior art. now run to the patent office and delete this message from all servers. Amateurs :-)

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Passive wire detection? is a bit trickier than *if* the wire were in someway supplied a signal. Your technique of simple metal detection would work *if* you combined it with the motion of moving towards the fence. It would be VERY difficult to detect a fence, sitting still, but move towards a fence and it will 'highlight' itself. More, later.

We used to do proximity fences that easily detected people at distances of 5-10 feet away, using the technique of supplying an electric field, then detect the field 'changes' caused by a person waliking up near to the fence. Note, again that a person moving EXTREMELY slowly was not detectable, but moving an inch per second set it off.

Ground penetrating radar, probably will work. Get an old 10GHz radar intrusion alarm sensor - don't know if they still make them. Back in early 70's HP made an excellent one sold around $100. Used a splitter; part went to the antenna and part went to the receiver for synchronous detection. The side bands and that doppler shift told you a lot. I remember they wanted to sell to boat owners for collision avoidance, or such. Anyway *if* you can find a radar based motion detector, you can use that. You may get some false positives on large plants but there should be a work around for that. Radar, with multiple receivers probably holds the most reliable, but most expensive solution for you.

Back to the passive technique using low frequency... Low frequency electonics are cheap and coherent detection holds a lot of power.

Use a laptop with a 24 bit sound card. With a 1/4 inch diameter reflective antenna, I can easily 'see' over 1 inch, so let's scale that up. 10 inch diameter, should be able to 'see' at least 40 inches. With separate receivers,you should be able to extend that range to way over 80 inches. Yeah. that'll work. So cost is around $300 for the laptop, $50 extra components, six months of software and you're done!

Is there a market? You gonna sell it? Is this just fence collision avoidance, or are you trying to robotically do a field?

If you're serious about pursuing this, contact me off line.

It does not make much sense to detect any stray fields from 50/60 Hz, since in a proper three phase system, the external electric and magnetic fields cancel quite well at longer distances.

In order to detect the fields from individual phases, you have to be pretty close, but then you are too close for crash avoidance :-(.

Anyone really actually using Mainnet or similar PLC/PLT systems these days ??

I thought that they were mainly developed to circumvent the Deutsche Telecom telephone wire monopoly in Germany.

At least in Europe PLC was used only on the 230/400 V LV wiring. The ISP had to transport the Internet signal to the MV/LV distribution transformer in some way and then distribute an aggregate of 1 Mbit/s up to 1 km.

The LV distribution network is somewhat symmetrical, thus suppressing some of the PLC radiation, at least that is what the PLC proponents are claiming to get their system approved.

In the house wire symmetry is not so good, especially when the live wire goes to the light switch and returns to the line feeding the lamp. This "detour" will act like a stub and can radiate quite a lot. There was even a fear that the combined radiation from houses would combine and create strong aggregate fields.

Thus, you might be able to detect houses with the PLC systems, but I doubt that you could detect LV open wire lines this way.

Apart for some network management signals around 100 kHz, the HV or MV lines do not carry any data signals.

On a sunny day (Sun, 17 Jun 2012 19:19:59 +0300) it happened snipped-for-privacy@downunder.com wrote in :

Have fun!

On a sunny day (Sun, 17 Jun 2012 18:50:38 +0300) it happened snipped-for-privacy@downunder.com wrote in :

I guess you could also emit a few MHz EMP, and look for typical reflections. The magnetic field must be very strong too, so a simple pickup coil like they used to record from old telephones could perhaps pick up the 50 Hz or 60 Hz. Finally powerlines are likely hotter than the environment, many choppers already have IR equipment, maybe powerlines could be detected by IR radiation. And for high voltage lines tehre must be a lot of charge around, you can light a fluorescent bulb stuck in the ground under those. A MOSFET input should see them from far away.

In high voltage lines, some low current discharge will occur around the insulator between the live conductor and grounded pole. This discharge will emit some UV light that might be detectable.

A decade ago I was a member of various working groups dealing with the PLC interference issues. Some members were quite agitated at that time, but I did not think this was a great threat, simply because PLC was not economically viable at those days, much less these days.

The main problem with PLC is that the losses in LV wiring increase quite rapidly at frequencies in the 10-100 MHz range, some of which was due to radiation from the wiring. In addition, due to all the stubs in the electric wiring, causing all kind of multipath effects, some frequencies were unusable at a specific site. The noise caused by various electric devices and the attenuation to power supply parallel filter capacitors, only a few (1-3) bits could be transferred in each symbol.

Thus, the total download capacity would be only a few 1-3 Mbit/s, shared by all customer served by the same distribution transformer site (hundreds of customers at least in Europe). This might have been OK, when only a few people used Internet and 128 kbit/s was considered broadband.

These days, when practically everyone is using Internet. usually several hours a day and the minimum expected transfer rate is 1 Mbit/s a distribution point with only a few Mbit/s total shared capacity would be useless.

As far as I know at least in Finland, all electric companies offering PLC have terminated this access years ago as economically nonviable.

How are you going to calibrate that?

e

depends on the amount of current being carried by the conductors.

The high tension wires [meaning widely separated conductors] carrying

1000A easily put out microTeslas at 600 feet, and it's pretty easy to measure down below 1nT. inverse square for 'infinitely long conductors, means you can 'see' them over 3 miles away. That should give you enough time, unless you're going really, really fast.

snipped-for-privacy@downunder.com wrote in news: snipped-for-privacy@4ax.com:

I believe the helicopter people would accept ANY method of detecting power lines in enough time to avoid hitting them. None seems to exist at this time,so what the OP wants to do is probably beyond today's tech capabilities. it's pretty much the same problem.

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dot com

Around 1980, Hughes placed an ad (yes, only an ad) in Aviation Week for a system to detect cables at a distance.

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On a sunny day (Sun, 17 Jun 2012 18:06:41 -0400) it happened "Michael A. Terrell" wrote in :

Hwo accurate does it need to be? 'close' should be good enough.

In magnetic coupling the signal strentgh versus distance is?

Example: L1 tuning cap C fence (this fence has inductance L2) ----^^^^--- | |------------------------------------------------------- | signal generator area with cows | 100kHz | Zi = 0 0 pic up coil | fence | ----------------------------------------------------------------------- fence not to scale

f res is set by L2 + L2 and C

I have used inductive loops over large area at frequencies around 100kHz. You need to tune the loop to get any real current in it, Then you can get a good measure of distance. Just one of many possibilities.

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L2)

| | |

| fence

|

From a moving tractor,on uneven ground? How are you going to control the resistance of all the splices, and close that loop, which could be several miles long?

sci.electronics.design Re: metal dector for barbed wire fences

Robert: You mentioned a 24 bit audio card with a 1/4 inch diamater reflective antenna - could you describe that antenna? "Reflective" implies directional which is of major intrest, especially with a 1/4 in. diameter. Radar, as you mentioned, is effective but somewhat expensive. Like the retail metal detecters, radar is designed for targets that are relatively small, ie a nugget of metal. Fences, on the other hand, are very long. Nearly infinitly so in this case. Hopefully, this length can be turned to advantage but exactly how is the current question. The detector is intended for a NC tractor generally but more specifically a tractor cutting hay. Fence detection would avoid turning into a neighbor's corn when dead reckoning errs and maybe serve as a guide for the initial cut around the outer perimeter. A market for such equipment certainly exists, but the cost of a corporate structure relatively safe from government intrusion would be high.

Hul

-Passive wire detection? is a bit trickier than *if* the wire were in

-someway supplied a signal. Your technique of simple metal detection

-would work *if* you combined it with the motion of moving towards the

-fence. It would be VERY difficult to detect a fence, sitting still,

-but move towards a fence and it will 'highlight' itself. More, later.

-

-We used to do proximity fences that easily detected people at

-distances of 5-10 feet away, using the technique of supplying an

-electric field, then detect the field 'changes' caused by a person

-waliking up near to the fence. Note, again that a person moving

-EXTREMELY slowly was not detectable, but moving an inch per second set

-it off.

-

-Ground penetrating radar, probably will work. Get an old 10GHz radar

-intrusion alarm sensor - don't know if they still make them. Back in

-early 70's HP made an excellent one sold around $100. Used a splitter;

-part went to the antenna and part went to the receiver for synchronous

-detection. The side bands and that doppler shift told you a lot. I

-remember they wanted to sell to boat owners for collision avoidance,

-or such. Anyway *if* you can find a radar based motion detector, you

-can use that. You may get some false positives on large plants but

-there should be a work around for that. Radar, with multiple receivers

-probably holds the most reliable, but most expensive solution for you.

-

-Back to the passive technique using low frequency... Low frequency

-electonics are cheap and coherent detection holds a lot of power.

-

-Use a laptop with a 24 bit sound card. With a 1/4 inch diameter

-reflective antenna, I can easily 'see' over 1 inch, so let's scale

-that up. 10 inch diameter, should be able to 'see' at least 40 inches.

-With separate receivers,you should be able to extend that range to way

-over 80 inches. Yeah. that'll work. So cost is around $300 for the

-laptop, $50 extra components, six months of software and you're done!

-

-Is there a market? You gonna sell it? Is this just fence collision

-avoidance, or are you trying to robotically do a field?

-

-If you're serious about pursuing this, contact me off line.