metal dector for barbed wire fences

[Hul Tytus]

sci.electronics.design
metal dector for barbed wire fences

Anybody here have any suggestions for possible ways to detect fence wire,
mostly 1, 2 or 3 levels of barbed wire but also some 8 inch square matrix?
Typical mounting would be on a tractor or trailer, so the detector would need
a sense of direction, ie looking outward not inward. Minimum range would be
around one foot with 4 feet probably optimum.
Typical retail metal detectors have a short range and need a metal free
environment, leaving the methods they use somewhat doubtful. Evidently, there
are detectors with seperate heads/coils and 1-5 foot ranges but, once again,
require a metal free environment.
One possible area would utilize rf antenna's, one transmiting and the other
recieving a reflection from the wire(s). A parabolic or corner reflector type
antenna maybe if not for the high frequency - two 12 inch antenna's would be
about max size and that's in the gigaherts range, which might be a problem.
Any suggestions along this line will be appreciated.

Hul

 

[Jasen Betts]

sci.electronics.design
metal dector for barbed wire fences

Anybody here have any suggestions for possible ways to detect fence wire,
mostly 1, 2 or 3 levels of barbed wire but also some 8 inch square matrix?
Typical mounting would be on a tractor or trailer, so the detector would need
a sense of direction, ie looking outward not inward. Minimum range would be
around one foot with 4 feet probably optimum.
Typical retail metal detectors have a short range and need a metal free
environment, leaving the methods they use somewhat doubtful. Evidently, there
are detectors with seperate heads/coils and 1-5 foot ranges but, once again,
require a metal free environment.

One possible area would utilize rf antenna's, one transmiting and the other
recieving a reflection from the wire(s). A parabolic or corner reflector type
antenna maybe if not for the high frequency - two 12 inch antenna's would be
about max size and that's in the gigaherts range, which might be a problem.

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

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

 

[[email protected]]

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

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 :-(.

 

[[email protected]]

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

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.

 

[[email protected]]

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.

 

[[email protected]]

http://www.astrosurf.com/luxorion/qsl-rfi-bpl.htm

Have fun!

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.

 

[Tom Del Rosso]

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.

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

 

[Chieftain of the Carpet Crawlers]

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

Any such system would be fraught with huge problems and will never be
implemented.

Better to use GPS and tell pilots they need to watch where they are,
where they are going, and FARTHER ahead of where they are going.

If you are in the air and are a pilot and are in the last 1000 feet
between you and the ground, you should be fucking watching where you are
going. Period.

 

[Bill Martin]

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.

Are cows reactive or resistant loads? They sometimes behave both ways...

 

[notbob]

Cows are not generally magnetic I think.

http://en.wikipedia.org/wiki/Cow_magnet

 

[Chieftain of the Carpet Crawlers]

The wire avoidance system needs to operate in a crowded urban area
with UNKINOWN cable dispersement. Translate that to mean somewhere in
the mideast with people stringing wires in unexpected places. GPS
would not help a lot

If you are at ANY altitude below 1000 feet, you had BETTER be watching
where the **** you are going. Period.

 

[Chieftain of the Carpet Crawlers]

Um..., Dont you guys read Aviation Week? In the US, Crop Dusters use
augmented GPS while airborn at centimetric acuracy. There are many,
many, patents to John Deer, etc for augmented GPS using a variety of
techniques. Some are free,some are pay to play.

Differntial GPS is cheap, and the Coast Guard/FAA/Private Industry
transmits correction signals, on LF beacons, via satellite, and
commercial FM stations, as well as dedicated, local, land mobile band
transmitters.

I wont get into helicopter wire detection in a open forum, but suffice
it to say, commercial and mil systems exist. Some are radar based,
some IR, some passive.

With the best one being an ALERT PILOT. Sheesh.

 

[Chieftain of the Carpet Crawlers]

That's fine for commercial flights. But one of the applications of cable
detection would be for military use. Where 1000 feet is pretty high. And
where the enemy isn't likely to provide you with an accurate GPS map of
their terrain.

Think about barrage balloons (http://en.wikipedia.org/wiki/Barrage_balloon)
used during WWII.

Ummm... no.

If you are below 1000 feet in a mil run, you would be fully briefed on
your terrain expectations on every vector. Otherwise, your operations
plan WILL be held to an altitude KNOWN to be above ALL obstructions.

 

[Chieftain of the Carpet Crawlers]

Almost everything in nature abhors a magnetic field and tries to get
OUT of it, except for iron, etc.

You are beyond silly.

Ever see the pattern at the north pole of Saturn?

Where is the Iron?

 

[Jamie]

Maybe a couple of insulating arms poking out, with steel cables or
maybe chains hanging down. Apply a reasonable voltage to the cables
and look for the big spikes that will happen when a chain hits the
wire. Vegetation or wood fencing will make softer spikes, so can be
filtered out.

Or extended balloons. They hit the barbed wire and pop.

You know, they sell back up camera's pretty cheap these days.

And if you really want to get fancy, you can use an industrial
fanless PC brick and drop a video decoding program in there using
a cheap USB camera..

Jamie

 

[Adrian Jansen]

sci.electronics.design
metal dector for barbed wire fences

Anybody here have any suggestions for possible ways to detect fence wire,
mostly 1, 2 or 3 levels of barbed wire but also some 8 inch square matrix?
Typical mounting would be on a tractor or trailer, so the detector would need
a sense of direction, ie looking outward not inward. Minimum range would be
around one foot with 4 feet probably optimum.
Typical retail metal detectors have a short range and need a metal free
environment, leaving the methods they use somewhat doubtful. Evidently, there
are detectors with seperate heads/coils and 1-5 foot ranges but, once again,
require a metal free environment.
One possible area would utilize rf antenna's, one transmiting and the other
recieving a reflection from the wire(s). A parabolic or corner reflector type
antenna maybe if not for the high frequency - two 12 inch antenna's would be
about max size and that's in the gigaherts range, which might be a problem.
Any suggestions along this line will be appreciated.

Hul

I cannot think of any fence detection system which likely to be more
effective than a pair of human eyes and a brain.

If you are looking for a method of delineating the edge of a paddock, so
a tractor on automatic guidance does not run into the fence, it might be
simpler to drive once around the paddock with a precision GPS unit
mapping the 'keep in' area. Then supply that map to the guidance system.

 

[Chieftain of the Carpet Crawlers]

elaborate

READ it again, dork.

HAVE YOU (pretty simple to get)

EVER (even more simple)

SEEN THE PATTERN (a reference to something real)

ON SATURN (Pure simplicity)

How could you be so stupid as to NOT get what was said?

I think you are an idiot who heard "nature abhors" one too many times,
and it became a favorite thing for you to bark out.

AGAIN, it was a silly remark, and THAT is being nice.

 

[Chieftain of the Carpet Crawlers]

No, I haven't 'seen' those patterns. What is your point mentioning
those patterns?

elaborate.

say something of value, that's all I asked.

YOU said NOTHING of value you when you made the "nature abhors" remark.

THAT is what the remark was about. I was thumbing my nose at your
stupidity and penchant to form statements based on some other use of a
phrase.

"Nature abhors a vacuum..." is the remark, and YOU convoluted a segment
of that in YOUR untrue contention that "all things in nature abhor
magnetic fields..." which is 100% retarded.

NOW do you have a fucking clue, asshole?

The "thing of value" is letting folks know that your pathetic remarks
were absolute fucking BULLSHIT!

You starting to get it yet?

 

[Chieftain of the Carpet Crawlers]

.. Very big
example is that living flesh is repelled by a magnetic field, but not
sure any one noticed until recently.

Cite, fucktard!

 

[Spehro Pefhany]

Cite, fucktard!

It's diamagnetism. Type I superconductors are perfectly diamagnetic
(within limits). Water is slightly diamagnetic.