On Fri, Apr 01, 2005 at 11:53:28PM -0600, Doug McLaren wrote:
| | I wasn't at the field during the latest episode, but I was there
| | when the first plane went in. We have an ICOM IC-R2 hand held
| | scanner. The transmitter was shut off but there was still a strong
| | signal on channel 16.
|
| The IC-R2 should let you hear the signal. Did it sound like a RC
| signal or did it sound different? Try both FM and AM -- it could be
| either. (It could also be something else, but the IC-R2 only does FM
| and AM, so that's all you've got to work with.)
To expand on what I was saying, Simon had a good idea with a dipole.
I wouldn't say it's as accurate as a Yagi, but it's pretty good, and
very easy to make.
Go to Radio Shack or Fry's or whatever and get a connector for your
receiver's antenna jack and a few feet of coax that fits the
connector. With an adapter, you might be able to use standard 10base2
or CATV coax and connectors.
Keep a few feet of coax, then cut the coax. Pull the strands on the
outside of the coax in one direction, and the wire inside in the other
direction. It's harder to explain what to do than it is to do it.
Find some other wire -- type doesn't matter -- and cut two lengths to
39 inches long (for 72.5 mHz. For other bands, the forumla is 234
ft/frequency in mHz) each. Solder/connect each wire to one of the
wires to the wires coming out of the coax, forming a T with wires
going out to the side and coax coming up.
Find some way to keep those two wires going straight out -- taping
them to a 2 meter dowel would work nicely. You might also want to
make a handle of some sort, but that's optional.
Once made, you plug it into your radio. The radio has a singal
strength indicator, and what you'll do is rotate the antenna so that
the indicator is at the minimum possible rating. (This is called the
`null' of the antenna. The `lobe', or strong reading, is when the
antenna is at right angles to the transmitter.) Once done, the two
wires of your antenna will be pointing towards and away from the
transmitter. (This is why a Yagi is better -- it'll say `the
transmitter is this way' rather than `it's either this way, or that
way'. But it's not a big deal.) Now walk somewhere else, and repeat
the procedure. With directions determined in two locations, if
they're far enough apart, you should now know approximately where the
transmitter is.
If the signal is so strong that your receiver always reports maximum
strength, just tune off frequency _slightly_ until the reading drops
enough to find the null. You could also try looking for a harmonic of
the frequency and try that (exactly double or triple the frequency of
what you're listening to. Instead of 72.5 mHz, you could try 145.0
mHz or 217.5 mHz.)
Transmitter hunting is as much an art as it is a science, but it's
easy to get started like this. And if the signal is constant (as
opposed to intermittent like many pager signals) and not too far away,
this procedure will probably let you find it in under an hour, and
that hour includes the time building your antenna :)
For more details, google for `transmitter hunting'.
--
Doug McLaren, [EMAIL PROTECTED]
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