I'm trying to get a land-based VHF marine monitoring station up and
need to make my antenna have some degree of directionality. I need to
know if there is a "simple" way for me get about a 180 degrees of
coverage versus 360 (in hopes of increasing my range in the right
direction).

The antenna (a 9db whip-type) will be mounted along side a
free-standing antenna tower and have a tip height of about 80 ft asl.
Without any directional feature that should give me a range of
somewhere between 16 and 17 miles (assuming the distant end antenna
height is 8 ft asl).

If there is aneasy way to make it somewhat directional and gain another
mile or two range (at least) that would be great.

Any ideas or am I "all wet?"

Ken

Go to www.arrl.org...
Look in their book section for the 'ARRL Antenna Handbook'..
Buy a copy of same...
Look in the VHF/UHF chapters at antennas..
Notice that mounting a vertical antenna 1/4 wavelength from the side of
a taller tower will cause the metal of the tower to act as a reflector
and therefore the antennas circular pattern will become a cardoid
pattern...
I leave the details to the student...

denny - amateur radio station K8DO

definer wrote:
I'm trying to get a land-based VHF marine monitoring station up and
need to make my antenna have some degree of directionality. I need to
know if there is a "simple" way for me get about a 180 degrees of
coverage versus 360 (in hopes of increasing my range in the right
direction).

The antenna (a 9db whip-type) will be mounted along side a
free-standing antenna tower and have a tip height of about 80 ft asl.
Without any directional feature that should give me a range of
somewhere between 16 and 17 miles (assuming the distant end antenna
height is 8 ft asl).

If there is aneasy way to make it somewhat directional and gain another
mile or two range (at least) that would be great.

Any ideas or am I "all wet?"

Ken

In article , Larry wrote:
"Denny" wrote in news:1154084481.658770.294700
:

Notice that mounting a vertical antenna 1/4 wavelength from the side of
a taller tower will cause the metal of the tower to act as a reflector
and therefore the antennas circular pattern will become a cardoid
pattern...


http://www.sinclairtechnologies.com/...es.aspx?id=268
7.5 dB in a cardioid pattern with all the dipoles on one side of the pipe
(or tower). Download the pdf manuals and have a look.

Sinclair will be there 20 years from now still with a perfect SWR. The one
on our repeater had to be replaced because the 250 mph winds from Hurricane
Hugo blew the top off the building it was on in '89. That's how long the
one that's up there now is...(c; Because the whole thing is a DC short
hooked to the tower, itself, it takes a direct lightning hit to destroy it.
For this reason, you install just the dipoles on the seaward side of the
towers, all in line, without the pipe....about 4' down from the top of the
tower, letting the tower take the lightning hits. That's how we do it at
1800 ft AGL...(c;

Nothing fiberglass survives up there.....


If a vertical is mounted on the tower side, use a top stabilizing rod.

The dipoles can also be staggered to even out distribution however
you want.

greg

Google 'vhf yagi'

Ian M

In article .com,
"definer" wrote:

I'm trying to get a land-based VHF marine monitoring station up and
need to make my antenna have some degree of directionality. I need to
know if there is a "simple" way for me get about a 180 degrees of
coverage versus 360 (in hopes of increasing my range in the right
direction).

The antenna (a 9db whip-type) will be mounted along side a
free-standing antenna tower and have a tip height of about 80 ft asl.
Without any directional feature that should give me a range of
somewhere between 16 and 17 miles (assuming the distant end antenna
height is 8 ft asl).

If there is aneasy way to make it somewhat directional and gain another
mile or two range (at least) that would be great.

Any ideas or am I "all wet?"

Ken


There are a number of antennas and mounting configurations that will
do what you want. Most are expensive but if your in the commercial
end of things it is just a business cost. Go find a "good" Land/Mobile
Radio Engineer with design experience, and pay him to do the design
right. You won't be sorry......


Bruce in alaska who used to consult a lot, in a past life......
--
add a 2 before @

"definer" wrote in message
oups.com...
I'm trying to get a land-based VHF marine monitoring station up and
need to make my antenna have some degree of directionality. I need to
know if there is a "simple" way for me get about a 180 degrees of
coverage versus 360 (in hopes of increasing my range in the right
direction).

The antenna (a 9db whip-type) will be mounted along side a
free-standing antenna tower and have a tip height of about 80 ft asl.
Without any directional feature that should give me a range of
somewhere between 16 and 17 miles (assuming the distant end antenna
height is 8 ft asl).

If there is aneasy way to make it somewhat directional and gain another
mile or two range (at least) that would be great.

Any ideas or am I "all wet?"

Ken


Use the tower as a reflector by mounting the 9 db antenna one half
wavelength away from the tower on the side of the tower in the direction you
want to signal to go.