VHF installation tips, faq,
captk...@webtv.net
Anybody ever use one of these? comments?
http://www.shakespeare-ce.com/electron/accessories/art-2.jpg
antenna FAQ
http://www.shakespeare-ce.com/antenna/ant-faq.htm
installation tips
http://www.shakespeare-ce.com/antenna/tipinst.htm
Bart Senior
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>Anybody ever use one of these? comments?
>
>http://www.shakespeare-ce.com/electron/accessories/art-2.jpg
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This looks like the typical cheap wattmeter. The nice thing about
this style is the small size. These mount great overhead and that is
a good place for the antenna wiring because it's generally out of the
way and still accessible.
What I don't like about these wattmeters is you have to use a switch
to change from forward to reverse power readings. But it's not too
much of a hassle. You will probably want it set for forward power
most of the time--so for yacht use it is good to have and fairly
cheap--I think they go for around $25-$35. Any wattmeter is better
than no wattmeter--I consider it essential to know my radio is
working, and how well.
A better style wattmeter are the crossed needle syle wattmeters. The
best of these have a remote head split off from the in line sensor.
For a SSB HF radio these are useful if combined with an antenna tuner.
I use the medium sized VHF/UHF cross needle watt-meters w/o the remote
head-- in the $99 range. It was the smallest cross needle type I
could find. You can find these at any Ham Radio Outlet type store.
An important factor is a mounting bracket to attach it to a wall or
ceiling mount point.
>
>
>antenna FAQ
>
>http://www.shakespeare-ce.com/antenna/ant-faq.htm
>
>installation tips
>
>http://www.shakespeare-ce.com/antenna/tipinst.htm
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The only thing that matters on antennas is height and then gain.
The place for an antenna is the top of the mast. A second lower mount
point is good for back up and accessibilty--too hard to fix an antenna
problem at the top of the mast underway. I'd have a short wire 3db
gain antenna up high and a higher gain6 db antenna lower--on the
assumption that it would be used primarily when the boat was not heel
excessively.
Gain is measured against a standard dipole dbd, or against a
theoretical isotropic point source--dbi. dbi is a higher figure than
dbd, most manufacturers use dbi. the difference is 3db. assume
rating are dbi unless specificed dbd.
If you are on a sailboat, and are healing over 3db is a good pattern
basically the pattern of a dipole. A higher gain antenna, when
heeled, will direct energy up into the air, or reflect it off the
water up in the air instead of horizontally--where you want it.
The next most important factor is getting as much of the power to the
antenna as possible.
If you have the room a good quality RG-8 feedline is the way to go.
The good stuff is 1/2" in diameter and may not fit up your mast very
well. Some masts have conduit attached to the inside--very hany for
feeding wire up the mast but perhaps limiting if you want to put lots
of antennas up there.
RG-213 is a type of RG-8--decent stuff but it's a less flexible than
mini-8. Mini-8 is 1/4" diameter feedline--thinner and more flexible.
Better get the best you can find. Anything sold in a marine chandlery
is probably not that good. Pick the cable with the lowest losses per
100'. If they can't tell you what that it-don't buy it. It must also
be 50 or 52 ohm impedance. I found 75 ohm video cable on my boat when
I bought it and corroded to nothing cheap connectors.
Connectors: I use silver plated teflon connectors whenever possible,
and nickel plated as a second choice.
Another common problem is impedance mismatch caused by corrosion in
the connectors. The proper way to connect UHF PL-259 connectors is to
squirt a dielectric insullator paste in the connector--I use a brand
called "Stuff". Then you fasten the connector. The insulator fills
all the voids and keeps water from getting into the connector. Once
the connector is tightened a good electrical contact is made. Wipe
off the excess, then wrap the outside with Co-Ax seal. This is a
waterproof tape with a sticky tar kind of material. Trust me on
this--this is the lasting solution for a marine environment.
If you skip the above steps as water gets in, you will need the above
discussed power meter to inform you that as time goes on, that the
connection is deteriorating as more and more power is being reflected
back to fry your radio.
Bart Senior
-. .---- . .
Peter Kennedy
installations. Its an inexpensive meter and not as sophisticated as the
more expensive models but it works very well and will detect problems in a
VHF installation such as bad antenna connections, as well as testing that
the output is up to spec.
--
Peter Kennedy
Peter Kennedy Yacht Services
Marine Electrical Systems
http://www.pkys.com
captk...@webtv.net wrote in message
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Anybody ever use one of these? comments?
http://www.shakespeare-ce.com/electron/accessories/art-2.jpg