Makes me wonder how high "Sea tow" in southflorida has their antennas.
I regularly talk to them from Bimini (40 NM from Miami) and Freeport
(55NM from WPB) for radio checks.

I have a 21' 9db 9 ft off the water (30' tall)
sqrt of 30 = 5.5 NM (My boat) That translates to 2500 ft... .Hmmmm
not possible.

Never really thought of it before but I bet they must have repeaters in
the islands.






Wayne.B wrote:

On Tue, 05 Jun 2007 06:40:26 -0700, wrote:


Hello, I need to set up a communication link between a shore station
and a dive boat that is at most 30nm (50 km) distance from the
shorestation (the shore station is on the beach i.e. there are no
obstacles between shore and ship)

Can somebody advice me if it is possible to do this with for exemple
2 Uniden Oceanus DSC VHF radioos and two 6 feet 6dB antennas? The Top
of the antenna would be about 16 feet aove sealevel on the boat and
about 30 feet on the shorestation?

Is there a better solution to assure the communiication . The radios
would be need for emergency cases)

Thanx fopr any input


6 db antennas and 30 feet of shore station height are not going to get
the job done reliably.

The standard equation for VHF range is 1.15 * SQRT height, with the
two calculated ranges added together. The boat has a clculated range
of about 5 NM and the shore station about 7 NM, for a total reliable
range of 12 NM.

I'd go with 9 db antennas at each end and increase shore station
height to at least 100 feet. Even that will be marginal, and you will
need to use low loss coax cable at the shore station tower. A tower
mounted pre-amp/amplifier would be even better.