"maisradios" wrote in message ...


Hello. Hopefully someone can clarify the following question. I have a
passive antenna for coverage of the frequencies of about 100khz to about
30 MHz. It's a 6 foot antenna, vertical made by the defunct RF Systems
Co. Holland.
It uses a feeder of Coax cable with 2 PL259s. The connection at bottom
of antenna has an SO 239. I get pretty good results with this antenna
and is not too noisy. My question is how to build an antenna like this
as I have no way to cut open the antenna and visualize what's inside,
unless I want to ruin the antenna. Would you think they use a coil of
wire inside the unit? If so, I wonder how much wire is there? And
finally the SO 239 at bottom of antenna unit means there would be a
ground inside the unit? Would this be another wire?
Any clarification on these questions would be appreciated.

================================================== ====

There may not be anything inside the housing. If there were a coil inside,
its purpose would to be to electrically lengthen the antenna -- useful for
bringing a transmitting antenna closer to resonant length but not terribly
useful at other freqs. Coaxial cable is used because of the shielding
value. (Close-by your listening location you may have computers, lights,
cordless phones, etc and it's nice to exclude interference (EMI). Thus,
coax is used between the radio and the antenna. This presumes the user is
clever enough to put the antenna itself as far as possible from EMI
sources.)

The base of the antenna has the SO-239 because it's cheap and convenient for
attaching the feed. The ground, if any, would be obvious. Nobody
intentionally hides a ground in the manufacturing process. Having said
that, I must add that a magmount antenna for a vehicle uses a ground that
couples to the vehicle body capacitively, through the paint. A ground on
the radio might be advisable. There are considerations of both safety and
reception when adding a ground. If used, the best grounds are usually short
and direct.

As to frequencies, don't worry too much when receiving. I have a minivan
whose fender-mount radio antenna (AM/FM/CD radio) gets ignition noise, so I
don't use it. Instead, I use an MFJ dual-band magmount antenna up on the
roof, cabled to the back of that radio. (I can disconnect it to use with my
H-T.) That crappy little magmount works just fine for both AM and FM radio.
It has no coils, no nuttin'. It's a piece of metal sticking up in the air
and the van radio thinks it's a nice antenna. Me smart, radio stupid.

"Sal"
(really KD6VKW)