Which VHF/DSC aerial?

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single

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I hate doing bits at the top of the mast so i want to replace the tatty fibreglass one while i'm there doing the anchor light. SO which aerial to go for? I have read the fibreglass type are better but which one?
 
A stainless steel 3' whip antenna will serve you best. They have the right radiation pattern for masthead work and the stainless construction will resist UV damage.
 
Better because?????? A fibreglass aerial is just a piece of wire in a tube. It cannot propagate any better than a piece of wire!! It may last longer as it is more protected.
Are you looking for longevity or maximum distance??

Salty John sells a Metz antenna that gets rave reviews for both performance and rugged build. If I was putting something on the top of a mast, it would be one of those.
http://www.saltyjohn.co.uk/metzmantavhfantennaaerial.htm
 
"Better" depends on the application. I believe nealry all the fibreglass aerials are designed for use on a mobo, presumably in part because a bare wire type whipping about near deck level risks serious injury to the crew. As a consequence most will also be designed with a radiation pattern to suit this type of vessel. Assuming that a mobo rolls and heels considerably less than a sailing yacht, the vertical spread of propogation of the design is less so a higher gain can be achieved. On a sailing yacht's masthead, the aerial does not need to be encapsulated (which can dissipate some of the signal, especially in rain) but needs greater vertical spread of propogation or else the signal will be transmitted to Mars on one side and Neptune on the other.

Rob.
 
Good, i have a new stainless whip as a spare so i'll use that. The ones that transmit to neptune and mars sound a bit ott for sailing;)
Second thoughts, that Metz Manta looks good.
 
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On the whole, new is good as cable and connections do deteriorate with age. Incidentally, I was thinking of the sea god Neptune. An antenna effectively propogates a horizontal dish of energy, so when heeled the windward side is inclined toward the clouds and the leeward side to the waves.

Rob
 
rob2 said:
On the whole, new is good as cable and connections do deteriorate with age. Incidentally, I was thinking of the sea god Neptune. An antenna effectively propogates a horizontal dish of energy, so when heeled the windward side is inclined toward the clouds and the leeward side to the waves.

Rob
Click to expand...
I'm replacing the lot including the radio, so it should be fine.To make life easier i'm putting it on the mizzen which is about 10' lower than the main.It won't affect range that much will it?
 
Salty John said:
About three miles less range, all other things being equal.
Click to expand...
John, I am glad that you are selling now the Metz DSC antenna for ICOM M802/1.

But I can not follow your calculation of the reduction of the radio horizont.
I am using
Distance (in nm) = 2.5 x sq root (High in meter)
Then I get for the 10 feet reduction of mast high from 16 to 13 meter a reduction of 1 mile in radio horizont
High Root 2,5
13 3,61 9,0
16 4,00 10,0 <<< this may work for a short check
18 4,24 10,6
21 4,58 11,5
24 4,90 12,2
27 5,20 13,0
30 5,48 13,7
33 5,74 14,4
36 6,00 15,0
39 6,24 15,6
Greetings, Wilhelm
 
funk-an-bord.de said:
John, I am glad that you are selling now the Metz DSC antenna for ICOM M802/1.

But I can not follow your calculation of the reduction of the radio horizont.
I am using
Distance (in nm) = 2.5 x sq root (High in meter)
Then I get for the 10 feet reduction of mast high from 16 to 13 meter a reduction of 1 mile in radio horizont
High Root 2,5
13 3,61 9,0
16 4,00 10,0 <<< this may work for a short check
18 4,24 10,6
21 4,58 11,5
24 4,90 12,2
27 5,20 13,0
30 5,48 13,7
33 5,74 14,4
36 6,00 15,0
39 6,24 15,6
Greetings, Wilhelm
Click to expand...

Wilhelm

It would be really good if you would use your "apparent" knowledge in helping the forum with solutions instead of questioning everything.
 
funk-an-bord.de said:
But I can not follow your calculation of the reduction of the radio horizont.
Click to expand...

Mea culpa. You are correct, Wilhelm.

I didn't make a calculation, I made a 'guestimate' in my head and assumed a reduction in height of both station antennas, sending and receiving. I also used convenient heights for the two stations so that I wouldn't over tax my aging brain trying to work the square roots - I assumed two stations at 49 feet compared to two stations at 64 feet. The answer is 2.8 nm which I rounded up to 3 nm.

I think my answer was OK for the purpose. I don't think the OP was looking for precision, just an indication of the effect of antenna height on range, so I didn't think it worth bumping the thread to make a correction.

By the way, it's important to get into the habit of calculating both sending and receiving horizon distances and adding them together to get range.

For anyone whose eyes haven't yet glazed over, the non-metric calculation is 1.4 x root H1 (in feet) plus 1.4 x root H2, the answer is nm. The constant 1.4, rather than the technically correct 1.23, takes into account the fact that radio waves can see about 15% beyond the horizon seen by the eye.
 
Yes, atmospheric conditions can have a huge effect. In certain conditions vhf signals can be carried huge distances - I think about 600 nm is the record!
And we have to remember that we only have 25 watts of power to work with, so it's important to get as much of that as we can up the cable and out of the antenna. Undersize cable, bad connectors and an inefficient antenna can rapidly consume much of that power.
 
A big thanks to Salty John for excellent and very quick service.Full new system up and running- Manta aerial,coax and connectors from John, coupled to a new Standard Horizon GX1700E. Fantastic;)
 
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