On Fri, 9 Nov 2012 14:08:13 +0000, Channel Jumper
wrote:
You really stuck your foot into this one Bruce, now you are going to be
stuck answering stupid questions for the next couple of weeks.
So much for diplomacy.
If you disassemble and Antron A99 or a Diamond X 500 -
$270 list for the Diamond X-510.
http://www.rfparts.com/diamond/x510series.html
The problem with such large antennas for VHF use on a vessel is that
they have too much gain. The vertical radiation angle is fairly
narrow. My guess(tm) is about 5 degrees at 450MHz and 10 degrees at
146MHz. As the vessels pitches and rolls, much of the RF is directed
into the water or into the sky, with very little going towards the
horizon. Unless one has a gyro stabilized platform, a lower gain
antenna might be more useful.
once inside, you
will find a piece of copper wire or steel wire or stainless steel wire
that is usually copper plated.
Inside a Diamond X50 dual band ham antenna.
http://802.11junk.com/jeffl/antennas/Misc/x50.jpg
Sorry about the lousy photo. It's badly stitched together from four
seperate photos. If you're wondering what happened, the former owner
leaned the antenna against the garage wall, and then backed his car
into it.
Between each section - spaced for certain wavelengths is capacitors of
unknown origin which makes the antenna into segments - some for 2 meters
and some for 70 CM.
This is what gives it its gain.
That's the brass sleeve section in the middle. The gain is provided
mostly by properly phasing the radiating sections so that the signals
add.
These are purpose built antenna's for those frequencies..
I should hope so. I would be seriously worried if they were built
without any purpose in mind. Perhaps for decorations as it's well
known that the uglier the antenna, the better it works.
You cannot take a Marine antenna - that uses a different frequency and
use it on amateur frequencies - due to the fact that there is no way to
get internally inside of the antenna and change the lengths of the
segments of the wires inside of the antenna.
You'll be amazed at how little is actually inside a marine antenna. I
don't have any photos handy. Most are copper tape glued to the inside
of the tube, errr... radome. The rest are variations on coaxial
(sleeve) antennas. However, for entertainment, I glued some magnetic
recording tape (ferrite) along the copper tape and was able to lower
the resonant frequency from about 156MHz to about 149MHz. That's not
enough for ham use, but does show that it can be done.
Most of them never built anything in their life and are just appliance
operators.
Again the diplomacy problem...
They do not make a tap and die or make one that is economically feasable
to repair a $10.00 antenna.. When you get into non standard threads -
if you can find a tap and die - they tend to be quite pricey..
We are talking $60 - $100 each...
http://www.ebay.com/itm/380414359502 $29
However, the dies are rather pricy.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558