T&T: VHF Antenna Question

[Milt Baker]

My thanks to those of you who took time to respond, both here and offline.

Sylvian:  Thanks for the tutorial.  I know that increasing the gain flattens the 
outgoing "donut" and does nothing to improve reception.   That notwithstanding,
I cannot see how it is that an 8-foot antenna out-performs a 16-foot antenna. 
VHF signals nominally are line-of-sight and a 16-foot antenna can "see"
farther than an 8-footer, assuming both start at the same level--and in my
case they do.

Greg:  The BOAT/US article was good.  However, my test is at the dock in
Fort Lauderdale where there is absolutely zero rolling.  The boat is far up a 
canal with essentially no chop or wind motion.  Moreover, I've noted the same 
problem both at sea and inport over many miles in the past year, which was
what got me chasing a solution in the first place.   What really called it to my
attention was when we were in Bermuda I could easily talk between 
Hamilton and St. Georges with the 6 DB gain antenna but not with the 
10.  I thought it might be a matter of receiver sensitivity but swapping
radios and antennas shows that the problem is with the 10 DB gain antennas
--or possibly their cables.

Jeffrey:  Cables--you may be onto something!  To answer your question, 
I did not swap cables because I am using the cables that came connected 
to both antennas.  There are no connections anywhere in the cables, and 
each cable was (presumably) connected to its antenna at the factory.  
Likewise, I am using PL-259 end fittings supplied by Digital Antenna and 
placed on the cables by DA.  We have not shortened any of the cables and 
are using the factory-supplied lengths without coiling them.  Still, I think 
the answer to the problem may lie in the cables--I just don't know what 
or why.   It's possible that the 6 DB antenna cable is shorter and that may
be the root of the problem . . . it's an avenue I'll pursue.

Rob:  I wish I could point to something blocking one antenna that is not
blocking the other, but they are located within about 10 feet of one
another and there's nothing nearby to block either one.  The closest 
house is about 50 feet away and while there are a couple of palm trees 
closer, I doubt they're causing the problem.  If so, I can't see why they
would affect one antenna but not the other.

For the record, we checked the VSWR of all three antennas and found
it to be perfect in every case.  That might also rule out a cable problem. 

I'm still mystified and still hoping for a call from Digital Antenna.  

--Milt Baker