What to use for an underground transponder?
Clint Alexander
source would be in the ground (anywhere between 3 - 10ft). The receiver
would need to locate it, much like a metal detector would except it would be
a small hand-held "wand" with a LCD giving the direction and signal
strength.
I'm not sure of the signaling to use therefore I'm not sure of the antenna
required. But, it would need it to follow part 15 of the FCC
rules/regulations (none hazardous and allows required interference).
I am completely new at this sort of technology. I have created circuits
before using L555 timer, 4046Phase Loop, etc. But I've never went farther
than building simple demonstration circuits. I wondered if there was anyone
on this list that may be able to shed some light on what I would need and/or
how I would use them (a schematical description), or even point me to the
"yellow brick road".
Thanks!
--
//Clint Alexander
Geoffrey S. Mendelson
> I want to make a simple transmitter to use as a locator beacon. But the
> source would be in the ground (anywhere between 3 - 10ft). The receiver
> would need to locate it, much like a metal detector would except it would be
> a small hand-held "wand" with a LCD giving the direction and signal
> strength.
Try burying a WiFi dongle and see what you get. 2.4gHz has the advantages
of being COTS (commercial off the shelf technology), easy to build
directional antennas, cheap and easily adapated to digital technology.
It also has the advantage of being legal in almost (if not) every country
in the world.
I'm not sure it will reach through 3-10 feet of dirt, but I expect that
anything much above 15khz will have that problem.
Geoff.
--
Geoffrey S. Mendelson, Jerusalem, Israel g...@mendelson.com N3OWJ/4X1GM
New word I coined 12/13/09, "Sub-Wikipedia" adj, describing knowledge or
understanding, as in he has a sub-wikipedia understanding of the situation.
i.e possessing less facts or information than can be found in the Wikipedia.
UKMonitor
wrote:
Try googling Avalanche / beacon / tranceiver / 457KHz
http://pistehors.com/backcountry/wiki/Gear/Avalanche-Transceivers
UKM
UKMonitor
Geoffrey S. Mendelson
> http://www.loc8tor.co.uk/Store/
I don't know what you are hiding, but some of the ELT (Emergency locator
transmitters) are tracked by satellite, and if you set one off sirens
go off in control centers.
Great if you are trying to get rescued, a disaster if you want to find
your "stash".
Jeff Liebermann
<g...@cable.mendelson.com> wrote:
>Try burying a WiFi dongle and see what you get. 2.4gHz has the advantages
>of being COTS (commercial off the shelf technology), easy to build
>directional antennas, cheap and easily adapated to digital technology.
2.4GHz won't work. It doesn't take much dirt or water to block a
wi-fi signal.
Besides 457Khz avalanche locators, look into Ground Penetrating Radar.
Most operate in the microwave region, but a few models work on very
low frequencies 50-500KHz. FCC Part 19 has a list of acceptable
frequency ranges. If you're tracking gophers, I vaguely recall seeing
an article that described the technology (but am too busy to go
Googling right now).
--
Jeff Liebermann je...@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
Clint Alexander
> your "stash".
That's funny :)
It would be for plotting tunnels from gopher, rabbits, etc. But I don't want
to buy COTS, I want to grab all the components myself, put the circuits
together on a few breadboards and make my own casing for it.
What's important is finding the simple components needed to implement this
type of operation. I've read into ELTs and MELs (Miner Emergency Locator) as
well, and while I have found a few circuit diagrams, they did not show what
antenna is being used and/or how that was connected to the circuit.
Here is a good example. If I use this oscillator:
http://yhst-27389313707334.stores.yahoo.net/i2c1kto68pro.html
(Voltage adjustable from 1KHz to 68MHz)
If we set this to work off of 1-5KHz:
A) How would I figure out what antenna is needed to send this signal through
10-20ft of dirt and concrete?
B) Where on a circuit would this antenna be attached? (directly connected to
the oscillator and 9-12V with perhaps a resistor in-between?)
--
//Clint Alexander
"Geoffrey S. Mendelson" <g...@cable.mendelson.com> wrote in message
news:slrni0afi...@cable.mendelson.com...
JIMMIE
Your friend the 555 may be just what you need. I will oscillate up to
around half a megacycle and have harmonics from DC to daylight.
Jimmie
Baron
>> Great if you are trying to get rescued, a disaster if you want to
>> find your "stash".
>
> That's funny :)
>
> It would be for plotting tunnels from gopher, rabbits, etc. But I
> don't want to buy COTS, I want to grab all the components myself, put
> the circuits together on a few breadboards and make my own casing for
> it.
>
> What's important is finding the simple components needed to implement
> this type of operation. I've read into ELTs and MELs (Miner Emergency
> Locator) as well, and while I have found a few circuit diagrams, they
> did not show what antenna is being used and/or how that was connected
> to the circuit.
>
> Here is a good example. If I use this oscillator:
> http://yhst-27389313707334.stores.yahoo.net/i2c1kto68pro.html
> (Voltage adjustable from 1KHz to 68MHz)
>
> If we set this to work off of 1-5KHz:
> A) How would I figure out what antenna is needed to send this signal
> through 10-20ft of dirt and concrete?
> B) Where on a circuit would this antenna be attached? (directly
> connected to the oscillator and 9-12V with perhaps a resistor
> in-between?)
Consider just how big the antenna might have to be at those frequencies.
300,000,000 divided by F in Hz = length in meters.
Using your 5Khz (300,000,000/5000) = 60,000 meters !
--
Best Regards:
Baron.
Clint Alexander
> 300,000,000 divided by F in Hz = length in meters.
> Using your 5Khz (300,000,000/5000) = 60,000 meters !
>
That's true. Okay -- I obviously would need a lower frequency to penetrate
ground; what would be a workable solution?
What if I took 10ft of antennae and just coiled it so it didn't take up so
much space?
Thanks for all the info!
--
//Clint Alexander
"Baron" <baron....@linuxmaniac.nospam.net> wrote in message
news:hu3rd0$qv3$1...@news.eternal-september.org...
AndyS
Andy writes: I messed with a transmitter used to map out caves and
tunnels a while back and think that would fit your bill. I don't
remember the details
but I think it ran around 100 Khz or so, and the antenna was just a
coil
of wire about a foot in diameter, using magnetic near field coupling.
Power was only a few watts and the range was hundreds of feet.
If you google things like "cave mapping" , " spelunking
transmitters",
and keywords like that, you may have a lead to follow.
Good luck,
Andy W4OAH
UKMonitor
>
> - Show quoted text -
At 457KHz they use ferrite rod antennas
I think if you are building your own system you need a crystal locked
transmitter and a very narrow bandwidth ( DSP filters ? ) receiver in
order to obtain the best range and rejection of unwanted noise and out
of band signals.
Some design notes can be found here.
http://www.ece.uvic.ca/~mblarows/ELEC499/documents/ELEC499A%20Progress%20Report%202-r1.pdf
http://www.backcountryaccess.com/english/research/documents/457andFuture_000.pdf
Google or search US patent websites for 457KHZ transmitter antenna.
UKM
UKM
Baron
>> Consider just how big the antenna might have to be at those
>> frequencies. 300,000,000 divided by F in Hz = length in meters.
>> Using your 5Khz (300,000,000/5000) = 60,000 meters !
>>
>
>
> That's true. Okay -- I obviously would need a lower frequency
Lower frequencies mean longer antenna. :-(
Also since 5Khz is in the audio range of frequencies you might be better
off with a coil based microphone.
> to penetrate ground; what would be a workable solution?
I think you need to do some more research. Its easier not to re-invent
the wheel.
> What if I took 10ft of antennae and just coiled it so it didn't take
> up so much space?
If you take any antenna and reduce its physical size you will also
reduce the amount of energy that it can radiate for any given input. I
forget the rule of thumb, but it goes something like inverse square.
Half the radiation quarter of the distance.
>
> Thanks for all the info!
--
Best Regards:
Baron.
Clint Alexander
> Lower frequencies mean longer antenna. :-(
Typo/Brain-fart -- I meant "higher" frequency
> I think you need to do some more research. Its easier not to re-invent
> the wheel.
I certainly do not wish to reinvent the wheel, but, I would like to carve
and sand my own wheel, though -- for commercial reasons.
I'm looking for the most lowest level of development that one could start
with given a humble work environment.
--
//Clint Alexander
"Baron" <baron....@linuxmaniac.nospam.net> wrote in message
news:hu5b62$qsn$1...@news.eternal-september.org...
Baron
>
>> Lower frequencies mean longer antenna. :-(
>
> Typo/Brain-fart -- I meant "higher" frequency
>
We all have them. :-)
>
>> I think you need to do some more research. Its easier not to
>> re-invent the wheel.
>
> I certainly do not wish to reinvent the wheel, but, I would like to
> carve and sand my own wheel, though -- for commercial reasons.
>
I've no problem with that ! But you do need to look at what work has
already been done by other people and try to understand what problems
they have had to overcome in order to achieve their goal. Then analyse
what you need to do to achieve your goal.
>
> I'm looking for the most lowest level of development that one could
> start with given a humble work environment.
>
Most entrepreneurs start of with an idea and develop it with very little
resources. But you have to ask the right questions and more important
understand the answers.
Radio propagation through the earth is one of the most challenging
problems you could attempt to solve. You seem to be concentrating on
very low frequencies, fine if you can tolerate very very slow data
flows. I'm sure there are frequencies that will propagate through the
earth fairly easily, but getting to a point where a usable signal
occurs with reliable results isn't easy.
Maybe more information about what you are trying to achieve would help
to point you in a better direction.
--
Best Regards:
Baron.
Roy Lewallen
>
> If you take any antenna and reduce its physical size you will also
> reduce the amount of energy that it can radiate for any given input. I
> forget the rule of thumb, but it goes something like inverse square.
> Half the radiation quarter of the distance.
That's not true. All the power delivered to an antenna is either
radiated or turned into heat -- antennas have to obey the law of
conservation of energy like everything else. The fraction which is
turned into heat is determined by the loss of the antenna, not its
physical size. Loss does generally increase as the size gets smaller,
but not by any fixed proportion to the size, and many small antennas can
be quite efficient.
Roy Lewallen, W7EL
JIMMIE
On the other hand an EM antenna may not best suit your job. I would
suggest feeding a buried coil and let this be half of a transformer
coupled to your receiver.
Jimmie
Dave Platt
Baron <baron....@linuxmaniac.nospam.net> wrote:
>Radio propagation through the earth is one of the most challenging
>problems you could attempt to solve. You seem to be concentrating on
>very low frequencies, fine if you can tolerate very very slow data
>flows. I'm sure there are frequencies that will propagate through the
>earth fairly easily, but getting to a point where a usable signal
>occurs with reliable results isn't easy.
It might be worth checking out some of the work done by Bonnie Crystal
KQ6XA and her cohorts. They've been able to communicate from the
earth's surface, down into caves (and back up), using LF and HF radio
systems.
--
Dave Platt <dpl...@radagast.org> AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Roy Lewallen
>
> Radio propagation through the earth is one of the most challenging
> problems you could attempt to solve. You seem to be concentrating on
> very low frequencies, fine if you can tolerate very very slow data
> flows. I'm sure there are frequencies that will propagate through the
> earth fairly easily, but getting to a point where a usable signal
> occurs with reliable results isn't easy.
Attenuation through the ground depends on the soil conductivity and
dielectric constant, and the frequency. Here's the attenuation in dB/ft
for two ground types and a number of frequencies:
Freq MHz Avg soil(1) Vy good soil(2)
0.01 0.037 0.091
0.1 0.12 0.29
1 0.35 0.90
10 0.66 2.4
100 0.69 3.3
10,000 0.69 3.4
(1) Conductivity = 0.005 S/m, dielectric constant = 13
(2) Conductivity = 0.03 S/m, dielectric constant = 20
So the distance you can communicate depends on these factors as well as
antenna efficiency, power, and receiver sensitivity.
Attenuation in salt water is very much higher, which is why submerged
submarines have to communicate at VLF.
Roy Lewallen, W7EL
Geoffrey S. Mendelson
> Attenuation through the ground depends on the soil conductivity and
> dielectric constant, and the frequency. Here's the attenuation in dB/ft
> for two ground types and a number of frequencies:
>
> Freq MHz Avg soil(1) Vy good soil(2)
> 0.01 0.037 0.091
> 0.1 0.12 0.29
> 1 0.35 0.90
> 10 0.66 2.4
> 100 0.69 3.3
> 10,000 0.69 3.4
So if I get this right, a 2.4gHz signal in normal soil would be anttenuated
6.9 db (less than 2 "S units). In very good soil, it would be anttenuated
around 34 db, which would make it difficult to receive.
A Pringles can antenna has a gain of about 18db, that would certainly be
enough for average soil, and might be good enough for very good soil.
It also has the advantage of possibly being a 2 way link.
Roy Lewallen
> Roy Lewallen wrote:
>> Attenuation through the ground depends on the soil conductivity and
>> dielectric constant, and the frequency. Here's the attenuation in dB/ft
>> for two ground types and a number of frequencies:
>>
>> Freq MHz Avg soil(1) Vy good soil(2)
>> 0.01 0.037 0.091
>> 0.1 0.12 0.29
>> 1 0.35 0.90
>> 10 0.66 2.4
>> 100 0.69 3.3
>> 10,000 0.69 3.4
>
> So if I get this right, a 2.4gHz signal in normal soil would be anttenuated
> 6.9 db (less than 2 "S units). In very good soil, it would be anttenuated
> around 34 db, which would make it difficult to receive.
Those dB values are correct for 10 feet of homogeneous soil. Real soil
is stratified, and reflections from layer boundaries could have some
pretty profound effects. 6.9 dB is from 2 to 4 "S-Units" on my Icom,
depending on where on the S meter scale it is.
> A Pringles can antenna has a gain of about 18db, that would certainly be
> enough for average soil, and might be good enough for very good soil.
Relative to what? According to this site
http://www.turnpoint.net/wireless/has.html, a Pringles can antenna
showed about the same gain as a Lucent omnidirectional antenna. Of
course, an 18 dB error is only a mis-estimation of power density by a
factor of 1,000,000,000,000,000,000. Pah, piddly nit-picking details.
You could make it up by increasing the power by the same factor.
> It also has the advantage of possibly being a 2 way link.
A reliable one would take some calculation, planning, and a realistic
idea of antenna performance.
Roy Lewallen, W7EL
Jim Lux
for subsurface comms and this sort of application, you typically use a
loop antenna, and accept the terrible efficiency of a physically small
antenna.
Look at the radios used by cavers for communication.
Clint Alexander
For all involved in the thread -- here's a perfect example. Sondes are
locator systems used in many areas (I think) such as pipelines:
http://www.rjmcompany.com/Pipe-cable-locator-RD2000-SuperCAT.htm
These have frequencies of 512hz, 8Khz and 33Khz
I'm searching for any specs now regarding crystal and antenna for both
transmitter and receiver. But I'm certain that the antenna isn't 1000's of
meters long ;)
If I'm reading this right -- I would want to build my own version of the
technology rather than purchase theirs'.
--
//Clint Alexander
"Clint Alexander" <cl...@cdalexander.net> wrote in message
news:paOdnc5uFrnIuJjR...@ptd.net...
UKMonitor
>
> - Show quoted text -
I think we need to know a bit more about your application.
I have one of these pipe / cable locators, you need to have a good
idea of the route the pipework its taking and then 'sweep' the
approximate area with the end of the locator. If you don't have a
starting point it's very time consuming to cover a large area.
The avalanche beacon permits initial detection over a much wider area
which considerably speeds up a 'blind' search.
What size transmitter (physical) are you able to use, Max weight,
Battery duration, required detection radius, depth of burial etc.
UKM
Clint Alexander
application for my needs.
Like I said previously, I want to build my own version. So we'll assume this
as the target technology leaving me with the question of what antenna would
be needed to perform these operations. I suppose the oscillator is just a
simple crystal or perhaps even voltage controlled (adjustable). I can use a
555 for this....
--
//Clint Alexander
"UKMonitor" <ukmo...@hotmail.com> wrote in message
news:8da92883-42c7-4dfe...@v37g2000vbv.googlegroups.com...
You
"Clint Alexander" <cl...@cdalexander.net> wrote:
> I'm searching for any specs now regarding crystal and antenna for both
> transmitter and receiver. But I'm certain that the antenna isn't 1000's of
> meters long ;)
Oh it is 1000's of meters Long, alright.... It is just all wound up in a
coil... with VERY thin wire.....
Clint Alexander
> Oh it is 1000's of meters Long, alright.... It is just all wound up in a
> coil... with VERY thin wire.....
Can I use any wire or does it have to be a certain kind?
I've asked about coiling wire but I didn't get any positive feedback.
However, it wasn't described as impossible.
--
//Clint Alexander
You
"Clint Alexander" <cl...@cdalexander.net> wrote:
You can use any Insulated wire, Plastic Insulated or Enameled..... Most
use a very thin enameled 22 Gauge or smaller, and may even be wound on a
Ferrite Core to increase the Impedance...
Richard Harrison
"You can use any insulated wire"
I agree.
I hound in tracing the location of large buried undrground pipelines,
the "cooperative method", a transmitter attached to the pipe with a
receiver sensing the signal on the pipe worked best. Due to ground
characteristics, the lower the frequency, the better. I used 12 Hz.
My transmitter used cpmplementary symmetry power transistors in its
output which fed a 400-Hz Variac which proved to work well as a variable
impedance matching transformer to the pipeline. Oscillator-amplifier and
Variac were about the size of a bread box and weighed much less than the
12-volt car battery which powered them.
The receiver was a common relay coil with an iron core which fed a
transistor amplifier which had its output rectified and metered. The
coil was attached to a stick which served as a wand. Divers used the
coil in rivers and oceans where it followed the signal very well, as on
land.
The strongest signal was when the core pointed directly to the pipe, and
checking the distance to either side of the pipe the signal could be
well received gave an estimate of the depth of the ground covering the
pipe, usually 6 to 8 feet in our case. I could go miles down the pipe
before the signal faded (once 8 miles).
I don`t know how applicable any of my pipeline experience is to animal
burrows but it works well with tracing buried conductors or wires in
walls for that matter.
Our pipelines also had rectifiers for cathodic protection and I also
keyed these on and off at low frequency to provide a unique signal to
follow.
Best regards, Richard Harrison, KB5WZI