How to Triangulate a Radio Signal
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ion is an effective method to find a radio transmitter. There are various methods but for Ham
radio, the most common method is by using a signal meter on a radio or scanner. Some can even
use the volume of the signal if they have good hearing. The basic method is shown in the
diagram shown.
As shown, the hiker measures the direction to the signal at one location, draws a line on a map,
moves to another location, draws another line. As long as the signal does not move the lines
should converge close to the target signal. But, as usual, it always does not work that way. Here
are some tips:
1. Direction to signal. You will need a meter to measure signal strength to the target transmitter.
The more narrow the receiving antenna the better as compass points are easier to plot with a
narrow line. On a Ham radio this is the S-Meter.
2. Directional antenna or attenuation. A tape measure antenna is best but any kind of Yagi
antenna will work for indicating signal strength changes relative to direction. It can be done
WITH AN HT as well by using your body to block the signal. To do this, put the radio and
antenna close to your chest where you can see the meter and turn slowly in a circle. The point
where the signal is weakest means the transmitter is directly behind you. This is because your
body attenuates the radio signal. You can also put the radio in a foil lined can and lower it with a
string until just the tip of the antenna is showing to weaken the radios receive sensitivity when
the signal is very strong and you can not get an S-meter change. As long as you do not transmit,
removing the antenna also helps.
3. Radio waves bounce. Careful that you are not getting a reading from the side of a building or
hill that is reflecting the radio wave. This always is the case so you must find open ground and
may have to take several readings to home in.
4. As you get closer, you will need to make the receiver less sensitive. Some people use
attenuators on the antenna feed, or remove the stronger antenna for a weaker one when very
close. When you are so close to the signal that the reflections behind you are almost as strong as
those in front, you can sometimes tune off frequency slightly to weaken the signal strength.
There are various methods and many sites on line can be helpful.
5. Be Safe. Please don't drive and search by your self. Even waving an antenna out the window
by a passenger can be dangerous. Park safely in a parking lot, then to your direction finding.
6. Be patient and watch your surrondings. Remember how radio waves can bounce, scatter,
defract or be absorbed by the environment. It is because of these that most radio communcaitons
are made as most are not truly line-of-site. So move around some and make sure your direction
readings do not change much to indicate true headings to the transmitter.
7. Practice. There is a lot of fun doing this. Do you know where your favorite FM or AM radio
is broadcasted from? Try this and find out. Those are easy because they are transmitting all the
time. You can find other targets to search out as well.
8. There are other methods such as time-delay and others that take more specialized
equipment, but Triangulation will serve you well if you practice it. Have fun!
---73- N5PUV---Credit for Image:
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