In article ,
Robert11 wrote:

Have a Scantenna antenna which I think is "pretty good". It's up in my
attic.

It's omni directional, and broadband over the typical scanner ranges
(supposedly).

I can often pick up coast guard conversations, but very rarely (but
ooccassionally) ship traffic.

Do you think a dedicated, very directional, and tuned to the marine freq's
would help, or am I just too far away ?

Could very well help, especially if you can get it up above the attic
into clear air. In fact, the height of the antenna may make more
difference than antenna gain/directionality.

My guess is that your current antenna is high enough up to pick up the
shore antennas (which are probably tower- or building-mounted) but is
too low to be in good line-of-sight to the ships themselves.

Review the page at http://www.connect802.com/height.htm - it has a
chart showing the required height-above-ground of an antenna, to "see"
another antenna past the earth's curvature.

Any thoughts on, or antenna suggestions would be most appreciated.
No idea what to buy, if you feel it's worth a try ?

Take a look at

http://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf

Simple, decent-performing Yagi antennas that you can throw together
with a piece of one-by-two wood for the beam, some stiff copper wire,
and a soldering iron.

I'd suggest taking the dimensions for the simplest (3-element) 144 MHz
antenna, and rescaling them all by a factor based on the _highest_
marine-band frequency you want to receive. You'll need to rescale the
element lengths, and the distances between the elements. You'll end
up with a Yagi which is intermediate in size between the 144- and
220-MHz versions.

Very interested in the AIS data being transmitted by ships at around 162
MHz, as well as general marine stuff.

BTW: really surprised that I hear the CG at all. I would have thought that
their antennas would be "focused" out to sea, with any propagation going the
other way (towards me) minimized to maximize the effectiveness of their
radiated power in the direction that it's needed.

At most, I'd think that they'd use an antenna with a cardioid or
off-center-circular pattern, so that a single shore station's signal
would cover the whole half-circle with fairly equal power. There's
probably still quite a bit of back-spill towards shore - plenty enough
for you to receive. They wouldn't use (or need to use) an antenna
with an extremely high front-to-back ratio, because they have no need
to "reject" transmissions from shore-side... since there probably
aren't any. Increasing the front-to-back ratio would just add
complexity and expense to the antenna, reducing its overall
reliability (more things to break), at no significant benefit in
received-signal quality or desired-direction output power.

--
Dave Platt AE6EO
Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior
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