Vince Fiscus, KB7ADL wrote:

I participate in a lot of transmitter hunts.

If he wants to hunt with an omni, all he needs really is a step
attenuator and a receiver with an S-meter. Leave the GPS at home.

I was thinking of using GPS too, but here is how I would do it. I have a
4 antenna doppler array that gives real time headings. The array is
mounted on my vehicle. The doppler unit sends four bit BCD to a 16 LED
heading indicator.


I believe there is a kit you can build:

http://www.ramseyelectronics.com/cgi...ction&key=DDF1

Vince Fiscus, KB7ADL wrote:

I participate in a lot of transmitter hunts.

If he wants to hunt with an omni, all he needs really is a step
attenuator and a receiver with an S-meter. Leave the GPS at home.

I was thinking of using GPS too, but here is how I would do it. I have a
4 antenna doppler array that gives real time headings. The array is
mounted on my vehicle. The doppler unit sends four bit BCD to a 16 LED
heading indicator.


I believe there is a kit you can build:

http://www.ramseyelectronics.com/cgi...ction&key=DDF1

Scott in Aztlan wrote
Ted Edwards wrote:

Suppose you were participating in a search for a hidden radio
transmitter, only
instead of the usual radio receiver with a directional antenna you have
a
receiver with an omnidirectional antenna and a GPS receiver.

What is the reason for the constraint?

The radio receiver in question has a built-in omnidirectional antenna and
no
jack for an external antenna.


Turn the whole radio/built-in antenna into a directional antenna by mounting
it 1/4 wavelength infront of a metal surface.

The metal surface can be tin foil over a piece of cardboard.

Rotate the radio and metal surface to find the direction of the signal.

Calibrate it with a known transmitter location first before you go hunting
for an unknown transmitter.

Scott in Aztlan wrote
Ted Edwards wrote:

Suppose you were participating in a search for a hidden radio
transmitter, only
instead of the usual radio receiver with a directional antenna you have
a
receiver with an omnidirectional antenna and a GPS receiver.

What is the reason for the constraint?

The radio receiver in question has a built-in omnidirectional antenna and
no
jack for an external antenna.


Turn the whole radio/built-in antenna into a directional antenna by mounting
it 1/4 wavelength infront of a metal surface.

The metal surface can be tin foil over a piece of cardboard.

Rotate the radio and metal surface to find the direction of the signal.

Calibrate it with a known transmitter location first before you go hunting
for an unknown transmitter.

Scott in Aztlan wrote.

all you have is a radio receiver with an
omnidirectional antenna which gives you a signal strength indication, the
assumption being that the RSSI is roughly proportional to the line-of-sight
distance between the transmiter and the receiver). The idea is to write a
computer program to take these position and RSSI values and prodce an
estimate
of the transmitter's location.


Dale DePriest wrote in message ...

It is an interesting idea theoretically. You could plot circles on a map
from the relative signal strength value and centered on the GPS
location, then increase the circle sizes proportionally until they
intersect and this will provide a rough idea of the location. With more
locations it would be better and better, throwing out some of the
circles that don't fit. It will probably work if you live in one of the
plains states and have a very sensitive RF meter and lots of driving time.

Dale

One problem is that when you get close to the transmitter the signal
strength meter hits the maximum and ceases to provide useful information. A
method for attenuating the signal is useful for this problem.

I like the intersecting circle idea. Remember to use the inverse square law
for the circle sizes. The power level of the signal will decrease by the
square of the distance from the transmitter. Its not linear.

A similar concept to the intersecting circles theory is that if you collect
a set of data along a straight line (by driving down a straight road) then
the transmitter is most likely on a perpendicular line crossing the road at
the point where you received the maximum signal. You can work around the
"maxing out the signal strength meter" problem by noting the two points on
the line where the signal shows maximum and then draw the perpendicular line
half way in-between.
This idea assumes the transmitter has an omni directional antenna as well.

Scott in Aztlan wrote.

all you have is a radio receiver with an
omnidirectional antenna which gives you a signal strength indication, the
assumption being that the RSSI is roughly proportional to the line-of-sight
distance between the transmiter and the receiver). The idea is to write a
computer program to take these position and RSSI values and prodce an
estimate
of the transmitter's location.


Dale DePriest wrote in message ...

It is an interesting idea theoretically. You could plot circles on a map
from the relative signal strength value and centered on the GPS
location, then increase the circle sizes proportionally until they
intersect and this will provide a rough idea of the location. With more
locations it would be better and better, throwing out some of the
circles that don't fit. It will probably work if you live in one of the
plains states and have a very sensitive RF meter and lots of driving time.

Dale

One problem is that when you get close to the transmitter the signal
strength meter hits the maximum and ceases to provide useful information. A
method for attenuating the signal is useful for this problem.

I like the intersecting circle idea. Remember to use the inverse square law
for the circle sizes. The power level of the signal will decrease by the
square of the distance from the transmitter. Its not linear.

A similar concept to the intersecting circles theory is that if you collect
a set of data along a straight line (by driving down a straight road) then
the transmitter is most likely on a perpendicular line crossing the road at
the point where you received the maximum signal. You can work around the
"maxing out the signal strength meter" problem by noting the two points on
the line where the signal shows maximum and then draw the perpendicular line
half way in-between.
This idea assumes the transmitter has an omni directional antenna as well.

Scott in Aztlan wrote:

What frequency?

2.4GHz.

Sounds like a microwave oven. :-) Wavelength is only about 125mm. You
could place the whole radio at the focus of a discarded parabolic dish.
You could even make a cylindrical paprabola out of cardboard and
aluminum foil.

Ted

Scott in Aztlan wrote:

What frequency?

2.4GHz.

Sounds like a microwave oven. :-) Wavelength is only about 125mm. You
could place the whole radio at the focus of a discarded parabolic dish.
You could even make a cylindrical paprabola out of cardboard and
aluminum foil.

Ted

Scott in Aztlan wrote in message ...
On Sun, 14 Sep 2003 02:28:28 GMT, Ted Edwards wrote:

Scott in Aztlan wrote:

What frequency?

2.4GHz.

Sounds like a microwave oven. :-)

Or a cordless phone... Or an X-10 wireless camera...



Or an 802.11B wireless access point?

Scott in Aztlan wrote in message ...
On Sun, 14 Sep 2003 02:28:28 GMT, Ted Edwards wrote:

Scott in Aztlan wrote:

What frequency?

2.4GHz.

Sounds like a microwave oven. :-)

Or a cordless phone... Or an X-10 wireless camera...



Or an 802.11B wireless access point?