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Author Topic: HELP !! With Fox Hunting ????  (Read 12518 times)

Posts: 8

« on: November 18, 2013, 09:00:11 AM »

I'm going to start off by saying I'm a complete and utter newbie so please don't get frustrated if I seem a little thick. However, I'm just grasping basics of radio
I'm looking to make a device that will help find trapped people in the dark in particular metal (steel) areas. From around 1.5M. So i thought the easiest way to so would be to use a cable tracer set up. So i found this;

Looks really good. But i have no idea how it works or if it will be any good??? I also thought about using radar which was even bigger head ache.

So i was wondering if you could help me the following;
-How does this device work ?
-Is it any good for my purpose ?
-Would Radar be better given my level of experience/needs ?

I appreciate  any help whats so ever.  Smiley Smiley Smiley

Posts: 12974

« Reply #1 on: November 18, 2013, 10:12:28 AM »

That particular device is used to identify a particular wire in a cable.  So, for
example, if you have a bundle of 44 wires and attach the signal source to one of
them, you can use the detector at the other end to determine which of the
wires is the right one.  Because of the sensitivity of the detector you may be
able to do this by touching the probe to the wire insulation without needing to
strip the wire.  This is handy for electricians fixing wiring, etc.

It works when the source and detector are connected by a wire, or very close
to that - it might detect within 1/4" or so of the wire, but not a lot further than
that.  So if everyone dragged a 20' wire behind them connected to a transmitter,
you would have a chance of finding the wire, but it wouldn't tell you the direction
or distance to the person.  (A standard avalanche rope marked with distance
and direction probably would be more useful in that case.)

It sounds as though you are looking for something that can be run along the
outside of a shaft or pipe, for example, and detect the location of a person
inside.  That is complicated by the fact that the steel will shield the detector
from a lot of types of signals (assuming it is solid, like a pipe:  if there are
enough joints in the metal that don't make good contact then enough signal
may leak out to make it more practical.)

It may be that an audio "beeper" of some sort is more practical - sort of the
electronic equivalent of tapping on a pipe.  That could be detected by ear
when one was close enough, or with a stethoscope listening to the metal. 
The louder the signal, the closer you are (to some extent at any rate.)  It may,
however, be rather annoying to have to listen to such a device all day at work,
so something in the ultrasonic (or infrasonic) range along with some sort of
electronic detector may be more acceptable.

A lot will depend on the exact details of the steel you have to detect the signal
through, how long it needs to be active, whether it can be manually enabled when
needed, etc.  The choice of frequency in particular will depend on many factors,
and may need to be determined by experiment.

Posts: 8

« Reply #2 on: November 18, 2013, 10:37:52 AM »

Thank you for the info. I was more looking for someway to find someone while in a container as such. So the device would be attach to someone and then if they went missing you could go in after and use the finder to get them. I was thinking could i use this device by wrapping coils of wire around them ( say there arm) and then putting fox generator and using the other device go and find the coil of wire. Bit crude allebiet. ??

Also why does this device produce a radio wave?? I can see what i think is darwinf pair and by stable flip flop . Then on the other side i assume its same but in reverse with the op amp powering the speaker.

Posts: 12974

« Reply #3 on: November 18, 2013, 11:04:19 AM »

That device creates an audio signal on the wire, and the detector is a high gain
audio amplifier that picks up the signal and plays it through a speaker.  It doesn't
use radio waves at all.

If you don't have to detect the person through the steel side of the container
then RF would work.  I'd use a fairly high UHF frequency if possible, because that
allows for a shorter antenna for the same directivity.  But in many cases you
could just sniff around for the strongest signal rather than using a directional
antenna (which can be prone to reflections when in a metal box.)  UHF (or higher)
also means that the transmitter antenna can be very small - just a small box
clipped to the belt.

An audio beeper might also work:  a dual 555 timer driving a speaker, and you
wouldn't need anything other than your ears to locate it.  Or a blinking LED
or strobe light, depend on what you expect to encounter inside the container.

If you want to get fancy, you can get one of the VK3YNG "sniffers" for the
450 MHz range.  They have audio readout of signal strength so you don't have
to see a meter in the dark, and they would also work with just a rubber duck
antenna to sniff for strongest signal.  Details here:
(Look at the photo near the bottom of the right side of the page.)

There are very low power 433MHz transmitter modules commonly available.  Over
such a small space you could just use a single transistor oscillator (possibly pulsed
to save battery power.)


Posts: 8

« Reply #4 on: November 18, 2013, 11:50:45 AM »

Hello Again, I really like VK3YNG. I will probably remove the speaker, And use a smaller antenna. If possible remove the tuning so locks onto 433MHZ. Smiley  Is there any other way i could make it smaller. Huh
« Last Edit: November 18, 2013, 12:01:10 PM by DEEGAN2909 » Logged

Posts: 12974

« Reply #5 on: November 18, 2013, 01:09:18 PM »

If you want directivity - that is, the ability to point it the direction of the transmitter,
rather than just sniff around and see where the signal gets stronger or weaker,
then you need a good antenna.  Unfortunately, antenna directivity is a function of
antenna size.  The sharper the pattern, the most distinct the indication of the
direction to the transmitter, and the larger the antenna for a given frequency.

If you need to use a small antenna, then either you can't have much of a
directional pattern, or you need a shorter wavelength (higher frequency) to
get a good pattern.  The 2.4 or 5.5 GHz wireless bands may be a better choice
in that case.  I've seen microwave radiation detectors with an LED bargraph
to indicate signal strength that might be pressed into service, as long as they
had enough sensitivity (which could be increased with an amplifier) to keep
the required transmitter power level low.

You need some sort of indicator to show the direction of the strongest signal.
On the VK3YNG sniffer the speaker is convenient for this (the output is an
audio pitch) especially if you have to climb around stuff and it isn't practical
to use headphones.

There is always a trade-off between transmitter power and receiver sensitivity
and/or complexity.  The stronger the transmitter, the simpler of a receiver will
be adequate to locate it, but the shorter the battery life of the transmitter will
be.  Typically the transmitter has to be on for much longer (whenever the person
is working in there) than the receiver (just when searching) so this dictates the
choice to some extent.  The Project Lifesaver system used for tracking patients
who wander away from home uses small wristband transmitters in the 216 MHz
range, but again I think the required receiving antenna would be larger than
you want.

With enough power it doesn't take a fancy receiver.  I've hunted for an aircraft
ELT beacon with just a crystal set connected to an antenna, because we wanted
something that could be used to check around an airport were we didn't have to
worry about the batteries going dead with it in long storage (it doesn't use any
batteries.)  With an Amplitude Modulated signal you can just turn the antenna for
maximum loudness in the earphones and go that way.  This approach wouldn't have
a lot of selectivity (the ability to distinguish the right signal among several) but
that may not be a problem in an enclosed container.  Again, using a microwave
band would allow shorter antennas, and the transmitter stability wouldn't be as
important because the receiver would still hear it if it drifted.

If you don't need a lot of receiver performance then they can be made quite small -
the required antenna us often the largest part, and the receiver circuitry can be
built inside the frame of the antenna.

There are many choices that would depend on the specific application.  For example,
whether the person would be relatively in the open (in which case a flashlight may
be all you need) or back behind piles of metal debris where you may only pick up
the RF signals bouncing off the roof of the container.  Something like a large metal
warehouse would have different requirements than finding someone inside of a
footlocker, or checking whether they were buried under paper in a dumpster.
Hunting for a radio signal inside a metal building is not a simple task because of
the multiple reflections, which is one reason that another approach (sound, light,
or a recovery rope tied to their foot) may work better in your specific application. 
Infrared imaging devices can pick up body heat.  All will depend on what sort of
material you expect to have between yourself and the person you are looking for.

You'll also have to consider what other equipment you plan to take with you to
perform a rescue, and whether the direction-finding unit would get in the way or
if you would have a free hand to operate it.

Posts: 12638

« Reply #6 on: November 18, 2013, 03:19:15 PM »

The problem with using any sort of RF inside a metal container is that the signal will be bouncing all over the place and it will be difficult to obtain an accurate direction. You'll probably be down to moving around looking for increasing signal strength. In order to make the best decision about the technology to use, one would need to know and understand the details of the application.

Assuming that the trapped person is able to talk and knows where he is, a simple two-way voice radio might be the most reliable.

Posts: 8

« Reply #7 on: November 18, 2013, 04:31:53 PM »

Im looking into ways of improving safety on ships. In particular when working in confined space ie tanks, anchor chambers etc. So i want a device that is strap onto a person body if they don't come back because they collapse due to lack of oxygen most likely. Rope is possible but when working it could easily be snapped or get snaged . I was hoping radio waves would be a feasible approach. Just give them a transmitter and then go in affect with a recviver pointing in the direction???

Posts: 12638

« Reply #8 on: November 18, 2013, 05:02:01 PM »

Are the spaces large enough that you have a hard time locating the person? If they are dark, how about a flashing red light that you could follow? How do you know that the person is down? Are you expecting the device to give notification to the bridge that a man is in trouble? It'll be difficult to get RF through the metal but each space could perhaps be equipped with a wireless sensor inside that was hard-wired to the bridge. The carried device could have a panic button and a mercury switch that would activate it if he goes horizontal. The device transmits a digitally encoded message containing his ID to the sensor inside the area which in turn notifies the bridge of the space location ID and the man's ID. The device also has a flashing light that activates so you can find him once you get inside the space.

The RF signal inside the space will be bouncing around making it difficult to use direction finding but it should work okay to activate a receiver (sensor) inside the space.

Posts: 8

« Reply #9 on: November 18, 2013, 05:12:23 PM »

Well you would hope he doesn't go tits up. Usually when working in this conditions there people that go in afterwards but due to poor lighting and visibility and lots of noise. We resort to sweep searching which takes forever. ( We've done drills and take about half an hour. ). So want to look at ways you could go with one of theses kits in ear. What about radar?Huh is that type of radio wave not really sure.

Posts: 12638

« Reply #10 on: November 18, 2013, 05:45:19 PM »

Yes, radar uses radio waves. They are designed to bounce off a surface and return to a receiver that is co-located with the transmitter - exactly what you don't want in this case. Light will reflect too but you can usually see what direction it is coming from and you don't need a special receiver. Of course if the space is such that he could be inside an enclosure within an enclosure then it won't work too well. On the other hand, if the space is open or has openings then you should be able to see the light and follow it to its source.

The reason that I'm thinking a strobe light is that it requires less average power for the same peak output so the batteries will last longer.

Posts: 8

« Reply #11 on: November 18, 2013, 05:52:00 PM »

Yeah,  its a tongue twisting and confusing problem.  Some space like tanks are very open and strobe lights are and would be affective. However, i need to make it intrinsic safe its going to go in say fuel tank. Then say a fire there be loads of smoke.  Hmmm...... Just need to give everyone radition and go in with a giger counter. haha . Might resort to using beacons and lights and then an audio cable tracer when closer.
« Last Edit: November 18, 2013, 05:54:53 PM by DEEGAN2909 » Logged

Posts: 12974

« Reply #12 on: November 18, 2013, 08:05:48 PM »

The audio cable tracer isn't going to work at all.  And given the ambient noise level
on ship (at least when the engines are running) I can see why an audio beeper won't
do much either (though it might be a useful backup in some cases - the sonar might
pick it up.)

A strobe would have the advantage that it could also be used if someone goes
overboard or has to signal an aircraft.  But whatever you carry it has to be something
that is turned on whenever one is in the compartment, and a strobe can be
annoying when it is continuously reflecting off of the surfaces around you while you
are trying to work.

Some sort of RF transmitter is probably the best approach, though be forewarned that
finding one in a hold full of metal debris takes some practice.  It could also allow you
to open a hatch and "sniff" the compartment to see if someone was in there.

To make that approach work you'd probably want something in the microwave
frequency range, though 433 MHz might work if you could tolerate the larger
antenna on the search receiver.  The beacon itself can be quite small - it would
depend on the desired battery life and what other features you wanted to put in the
same case.  (The watchband transmitters used for Project Lifesaver run for about
3 months continuously, and  can be heard up to 1/2 mile away in a clear area.)

If you look around for designs for WiFi antennas on the web you'll find lots of them,
typically of two types:  directional antenna, or omnidirectional ones for base stations.
The directional ones (typically a horn, helix, reflector, bent wire of some sort, etc.)
will give you an idea of the size antenna you might need if you used 2.4 GHz.  Here
are some examples:

These typically run 2 to 6 inches in diameter and 8" to 18" long, depending on
the specific design, the materials used, and the desired gain.  There are some other
options as well, but you'll get the idea.  The receiver could be built into the back end
of some of these to make a single unit.  You don't want too much gain, but
enough to enable you to resolve a direction within 30 degrees or so.

For the same gain, the antenna size decreases with frequency.  That's why small
directional antennas are more practical on the higher microwave frequencies (such
as 2.4 GHz.)  Of course, if you have a WiFi access point in a particular compartment
you may pick up that instead! 

The receiver then needs to have some way to indicate the relative signal strength,
because what you have to do is turn the antenna until the signal is strongest, in
which case you should be pointing in the direction that the signal is coming from.
(Which might not be the shortest direction to the source if it is bouncing off the
wall of a compartment, but it's the best you can do - you'll just find that the
direction changes as you approach the wall.)  Something like an LED bargraph
display may be adequate, though one potential problem is trying to squeeze
enough display range to allow you to indicate the direction both when the signal
is weak (the other end of the hold) or just a couple of feet away.  There are
several ways around this, such as a manual RF gain control (requires more
training to use), a display with lots of resolution (which isn't easy, especially
if you need to read it under difficult conditions), or some sort of automated
range indicator (as is done on the VK3YNG unit.)  I like the audio indicator
because it means I can look where I'm going or where the unit is pointing
rather than at the unit, though it may be difficult to use in a noisy environment
even with headphones.

Now I don't know of any ready-made direction-finding (DF) receivers for
the microwave range.  There may be some designed for finding WiFi networks,
but most of those probably will run from a laptop computer, and you don't
want to have to carry one of those with you.  The circuitry isn't difficult to
design, and you may be able to convert some equipment from another
purpose by adding a signal strength indicator to it.  But you'll want to run
some tests to see what sort of coverage you can get and how much power
you need, then design the overall system from there.

There are some other types of DF units that use loops, a pair of antennas, and
some other methods, and I don't think any of them will work well in your
situation due to the large number of reflections from all the metalwork.

Posts: 8

« Reply #13 on: November 19, 2013, 03:55:17 AM »

I like the idea of micro waves but aren't there health risk in strapping one onto a person??? As for Wi-Fi would a raspberry PI running a version of Linux would work. You could but a display on the HMDI a bar graph say and a Wi-Fi antena via the USB. Or is that just being an idoit??? Would this Wi-Fi show up on a laptop?Huh
Also thank you again for your time and help. Its really appreciative.

Posts: 8

« Reply #14 on: November 19, 2013, 07:41:11 AM »

Also, if i made a transmitter that was 2.6GHz or just out of the wi-fi spectrum would that work???
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