Chuck wrote:


The range is ~ 1.4 times the square root of the sum of the antenna
heights.

This should've said ~1.4 times the sum
of the square roots of the antenna heights.

Range is in statute miles; heights are
in feet.

Chuck

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

In article ,
Larry wrote:

Chuck wrote in news:1181052689_15255
@sp12lax.superfeed.net:

Antenna heights are insufficient for
reliable communication over that
distance. The combined antenna heights
would need to be more than 400 feet for
marginal line-of-sight communication.



I agree with Chuck. Marine radio is useless over-the-horizon more than
5% of optical line-of-sight.

Contact your local 2-way radio shop and ask them about installing TRUNK
RADIOS in both the shore installation and on the boat. The trunk radio
systems use very-high-up digital repeater stations that are widely
interconnected by computers that talk to the trunk radios, not unlike
what a Nextel iDen phone does, but on a much more powerful scale. These
trunk radio systems are shared by many diverse users, who rent service on
them for a pittance of what the entire trunk radio system costs.

Look in your local phone book under "2-way radio" or "trunk radio
systems" or "radio communications".

Professional communications, especially where life and limb might be in
danger, is well worth paying for. It's why the cops all use trunk radio
systems!

Larry

Ok, another Note here, from years of Parctical Experiencein the North
Pacific, 50 Statute Miles VHF Range is very common between Commerical
Shipping, WHERE the antennas are mounted on the TOP of the Masts, and
about 75 to 100 Feet above the water. Comms with HIghSite USCG Stations
that are in the 3000 Ft Range, above SeaLevel, are routinely carried out
out to 90 Statute Miles from these Commercial Ships. In the Bering Sea
it is very typical for the Crab Feet (Deadliest Catch type vessels)
to have good VHF Comms in the 30 to 45 Statute Mile range, and
significantly farther is they both are on TOP of the 30Ft Seas
that typically run in the winter storms. I have Installed, Licensed,and
Inspected, both Public and Private Coast Station, that have typical
30 to 45 Statute Mile coverage, to typical Fishing Fleet (less than 200
Tons) Vessels where the Coast Station Antennas are at the 75 to 100Ft
above Sealevel and the Vessel Antennas are in the 30 to 45 Ft level
range. In the US, VHF Limited Coast Stations are allowed 50 Watts
Carrier Power AT the Antenna Terminal, which allows for higher powers at
the Radio to make up for Feedline Losses. A good OmniDirectional High
Gain VHF Antenna (Cellwave/Phelps Dodge Super Station Master) at the
end of a 150ft run of 7/8" Heliax, with Beldon 9913 Jumpers, is about
the best that can be done for a Limited Coast Station. It makes sense
to put it (the coast Station) on the closest Hill, to the Coast, as
possible for whatever elevation gain you can get, without sacraficing
you limited range to Sea.

Beyound that you loking at SSB, or in the modern era, a TracPhone or
similar. These are going to cost you $2k to 3K by the tme you get them
installed and provisioned.

Bruce in alaska
--
add a 2 before @

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.

Ed wrote:
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.


Hi Ed,

The Sea Smart network uses 300' - 400'
towers in a radio-over-internet system.
I don't know if they have transmitters
on the islands, but if so, they are
probably linked by internet rather than
radio. The website mentions only US
coastal areas as their service territory.

http://www.seasmartvhf.com/pressroom...nes020606.html
Welcome to Sea Smart - "Who knew your
VHF was so powerful?"

Chuck

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----
http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

On Jun 7, 12:38 pm, Chuck wrote:
Ed wrote:
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.

Hi Ed,

The Sea Smart network uses 300' - 400'
towers in a radio-over-internet system.
I don't know if they have transmitters
on the islands, but if so, they are
probably linked by internet rather than
radio. The website mentions only US
coastal areas as their service territory.

http://www.seasmartvhf.com/pressroom...nes020606.html
Welcome to Sea Smart - "Who knew your
VHF was so powerful?"

Chuck

----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==----http://www.newsfeeds.comThe #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

VHF radios are meant to have a range of about 80 miles. Radio waves
travel really well over the water and there is very little loss over
long distances. I would try VHF first before investing in SSB or HF.