Hello,

I'm not certain this is the appropriate newsgroup for this question,
but if it isn't, I'd appreciate any referrals to other forums.

In many posts dealing with "foxhunts" and radio tracking situations, I
hear directional antennas discussed, or triangulation via a moving
receiver. But what are the relevant parameters if the receiving
stations are fixed?

Partly for the fun of it, and also for practical uses, I'd like to
design a receiving system whereby a small transmitter could be
located. This would not technically be a "tracking" situation, since
the transmitter would not always be on. I'm imagining something like
a garage door opener, where pushing the button can send a brief (but
very strong if necessary - this may have power implications?) signal.

The reason I ask about the non-directional solution is because I have
access to a plot of land approx. 300 x 300 feet square, with no
restrictions on building antennas on the four corners of the property.
I'm guessing such a system could be more accurate than a directional
system at a given power level, but the technical aspects of the
situation are beyond me.

I am a mathematician by trade, but know a smattering of electronics.
It would seem, at least in theory, that the relevant parameters here
are the distances between the 3-4 antennas (would a 4th help?), and
the strength and frequency of the signal. I also realize that some
processing of the signal would need to be done at the receiving end.
Perhaps the triangulation can be handled by software?

Any advice, direction, URLs, or discussion is much appreciated.

-wp

Washed Phenom wrote:
Partly for the fun of it, and also for practical uses, I'd like to
design a receiving system whereby a small transmitter could be
located. This would not technically be a "tracking" situation, since
the transmitter would not always be on. I'm imagining something like
a garage door opener, where pushing the button can send a brief (but
very strong if necessary - this may have power implications?) signal.

Try this one:
http://members.aol.com/BmgEngInc/Adcock.html

73, Markus HB9BRJ

Washed Phenom wrote:
Partly for the fun of it, and also for practical uses, I'd like to
design a receiving system whereby a small transmitter could be
located. This would not technically be a "tracking" situation, since
the transmitter would not always be on. I'm imagining something like
a garage door opener, where pushing the button can send a brief (but
very strong if necessary - this may have power implications?) signal.

Try this one:
http://members.aol.com/BmgEngInc/Adcock.html

73, Markus HB9BRJ

(Washed Phenom) wrote in message om...

Partly for the fun of it, and also for practical uses, I'd like to
design a receiving system whereby a small transmitter could be
located. This would not technically be a "tracking" situation, since
the transmitter would not always be on. I'm imagining something like
a garage door opener, where pushing the button can send a brief (but
very strong if necessary - this may have power implications?) signal.

The reason I ask about the non-directional solution is because I have
access to a plot of land approx. 300 x 300 feet square, with no
restrictions on building antennas on the four corners of the property.
I'm guessing such a system could be more accurate than a directional
system at a given power level, but the technical aspects of the
situation are beyond me.

I am a mathematician by trade, but know a smattering of electronics.
It would seem, at least in theory, that the relevant parameters here
are the distances between the 3-4 antennas (would a 4th help?), and
the strength and frequency of the signal. I also realize that some
processing of the signal would need to be done at the receiving end.
Perhaps the triangulation can be handled by software?

Any advice, direction, URLs, or discussion is much appreciated.

Accurate signal strength measurements are surprisingly difficult.
Ground reflections can combine to to double the signal strength,
or nearly cancel it out. Hams and broadcasters often use the term
"picket fencing" to describe the rapid fluctuations in signal strength
that occurs with fixed to mobile signal paths.

Not that your task is impossible, just hard. Perhaps a sufficient number
of signals can be simultaneously processed to statistically reduce the
signal combination/cancellation effect to an acceptable error.

Zack Lau W1VT

(Washed Phenom) wrote in message om...

Partly for the fun of it, and also for practical uses, I'd like to
design a receiving system whereby a small transmitter could be
located. This would not technically be a "tracking" situation, since
the transmitter would not always be on. I'm imagining something like
a garage door opener, where pushing the button can send a brief (but
very strong if necessary - this may have power implications?) signal.

The reason I ask about the non-directional solution is because I have
access to a plot of land approx. 300 x 300 feet square, with no
restrictions on building antennas on the four corners of the property.
I'm guessing such a system could be more accurate than a directional
system at a given power level, but the technical aspects of the
situation are beyond me.

I am a mathematician by trade, but know a smattering of electronics.
It would seem, at least in theory, that the relevant parameters here
are the distances between the 3-4 antennas (would a 4th help?), and
the strength and frequency of the signal. I also realize that some
processing of the signal would need to be done at the receiving end.
Perhaps the triangulation can be handled by software?

Any advice, direction, URLs, or discussion is much appreciated.

Accurate signal strength measurements are surprisingly difficult.
Ground reflections can combine to to double the signal strength,
or nearly cancel it out. Hams and broadcasters often use the term
"picket fencing" to describe the rapid fluctuations in signal strength
that occurs with fixed to mobile signal paths.

Not that your task is impossible, just hard. Perhaps a sufficient number
of signals can be simultaneously processed to statistically reduce the
signal combination/cancellation effect to an acceptable error.

Zack Lau W1VT

Do you have any frequency ranges in mind? A VHF system would be vastly
different in size than shortwave for example.

jw
K9RZZ

Do you have any frequency ranges in mind? A VHF system would be vastly
different in size than shortwave for example.

jw
K9RZZ

Zack Lau wrote:

(Washed Phenom) wrote in message om...


Partly for the fun of it, and also for practical uses, I'd like to
design a receiving system whereby a small transmitter could be
located. This would not technically be a "tracking" situation, since
the transmitter would not always be on. I'm imagining something like
a garage door opener, where pushing the button can send a brief (but
very strong if necessary - this may have power implications?) signal.

The reason I ask about the non-directional solution is because I have
access to a plot of land approx. 300 x 300 feet square, with no
restrictions on building antennas on the four corners of the property.
I'm guessing such a system could be more accurate than a directional
system at a given power level, but the technical aspects of the
situation are beyond me.

I am a mathematician by trade, but know a smattering of electronics.
It would seem, at least in theory, that the relevant parameters here
are the distances between the 3-4 antennas (would a 4th help?), and
the strength and frequency of the signal. I also realize that some
processing of the signal would need to be done at the receiving end.
Perhaps the triangulation can be handled by software?

Any advice, direction, URLs, or discussion is much appreciated.


Accurate signal strength measurements are surprisingly difficult.
Ground reflections can combine to to double the signal strength,
or nearly cancel it out. Hams and broadcasters often use the term
"picket fencing" to describe the rapid fluctuations in signal strength
that occurs with fixed to mobile signal paths.

Not that your task is impossible, just hard. Perhaps a sufficient number
of signals can be simultaneously processed to statistically reduce the
signal combination/cancellation effect to an acceptable error.

Zack Lau W1VT

Doing it by carrier phase would be better, if you could arrange a phase
reference. With hard-mounted receivers (or with a 2nd transmitter in a
known location) you can broadcast a time reference and do a reverse-GPS
sorta thing.

The higher the carrier the better the measurement, but with a lot 100
meters on a side you probably also want to send some sort of time
reference (you do get to design the transmitter as well, right?).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

Zack Lau wrote:

(Washed Phenom) wrote in message om...


Partly for the fun of it, and also for practical uses, I'd like to
design a receiving system whereby a small transmitter could be
located. This would not technically be a "tracking" situation, since
the transmitter would not always be on. I'm imagining something like
a garage door opener, where pushing the button can send a brief (but
very strong if necessary - this may have power implications?) signal.

The reason I ask about the non-directional solution is because I have
access to a plot of land approx. 300 x 300 feet square, with no
restrictions on building antennas on the four corners of the property.
I'm guessing such a system could be more accurate than a directional
system at a given power level, but the technical aspects of the
situation are beyond me.

I am a mathematician by trade, but know a smattering of electronics.
It would seem, at least in theory, that the relevant parameters here
are the distances between the 3-4 antennas (would a 4th help?), and
the strength and frequency of the signal. I also realize that some
processing of the signal would need to be done at the receiving end.
Perhaps the triangulation can be handled by software?

Any advice, direction, URLs, or discussion is much appreciated.


Accurate signal strength measurements are surprisingly difficult.
Ground reflections can combine to to double the signal strength,
or nearly cancel it out. Hams and broadcasters often use the term
"picket fencing" to describe the rapid fluctuations in signal strength
that occurs with fixed to mobile signal paths.

Not that your task is impossible, just hard. Perhaps a sufficient number
of signals can be simultaneously processed to statistically reduce the
signal combination/cancellation effect to an acceptable error.

Zack Lau W1VT

Doing it by carrier phase would be better, if you could arrange a phase
reference. With hard-mounted receivers (or with a 2nd transmitter in a
known location) you can broadcast a time reference and do a reverse-GPS
sorta thing.

The higher the carrier the better the measurement, but with a lot 100
meters on a side you probably also want to send some sort of time
reference (you do get to design the transmitter as well, right?).

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

(Washed Phenom) wrote in message om...


Any advice, direction, URLs, or discussion is much appreciated.


Thanks for the replies so far. They've been helpful, and have sent me
on some interesting Google searches learning a lot about RDF in
general. Some more specifics:

I have no preferred frequency ranges, but that is more out of
ignorance than flexibility! In terms of transmitter power, in my
first post I mentioned that a continuous signal wasn't necessary if
that would help matters. It seemed plausable to me that a transmitter
which used its power to transmit a short, strong signal could be
detected at a much longer range than a weaker signal.

The reply regarding carrier phase was interesting, and sent me on a
tour of GPS basics. Half the fun of this project is going to be
learning new stuff. As I understand it, the reason you called this a
"reverse GPS" is because the multiple receivers are in known locations
instead of multiple transmitters. It would be feasible to build a
second transmitter (a time reference?) and place it somewhere in the
100 yard square. There is a house roughly in the center of the
property which would be where the "guts" of the processing equipment
would be anyway. How does the carrier phase solution compare to VHF
and shortwave in terms of power requirements, size of transmitter,
etc?

Just to get a better sense of whether the range and resolutions I'm
looking at are feasible, suppose you wanted to locate your local
college radio station's transmitter. I just googled a few college
stations and found two FM stations that transmit at 300 and 400 watts.
The 300 watt station claims to cover 700 square miles. Of course I
realize that: 1) "covering an area" may not be equivalent to "area
within which their location can be pinpointed", and 2) Even if I could
generate such power in a portable transmitter, I would need to choose
bands so as not to run afoul of the FCC. (Just how much transmitting
power can be generated from a garage door sized unit is another issue,
and another reason the brief "burst" signal sounded preferable).
Anyway, I was sidetracked there. To get back to the main question, if
you had antennas at 4 corners of a 300 x 300 ft square lot, are there
any good thumbnail estimates of how accurate you could be at locating
the 300 watt college station, and how this accuracy varied as a
function of the distance to the station?

In addition to being a fun way to learn new things and tinker with
electronics, this project is also motivated by someone I care a great
deal about who often works in isolated outdoor locations and doesn't
own a cell phone or GPS. I know when she is at these sites, but worry
she will be unable to call for help if something happens. Can she be
located by her pushing a button and at what range?

She's already suggested building a Bat-Signal, but that is beyond by
technical expertise. Also, she said that buying her a cell phone and
GPS would be cheaper than building this monstrosity, but I like
intellectual challenges and need to keep my mad scientist reputation
well-exercised.

Thank you again, and please continue the excellent discussion.

-wp