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Old 17-02-2009, 03:01   #1
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Radio and Antenna installation question

It has occured to me that there are alot of questions as to what is the best antenna or how to install my HF radio. I am wondering if there has ever been a study done by some third party electronics expert (with the math to back it up) as to which antenna or antenna type is the best and what is the best way to install your rf ground. What is the best coax, etc. or at least what the different types are and how each performs compared to the others.

I know that all boats are different, but I am sure that there must be some information applicable to all S/V of the size commonly used here. If such data does exist, where does one get ahold of it? I would think that a manual with pictures and explicit or general instructions would be a great help.

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Old 17-02-2009, 03:10   #2
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Your are probably right in that someone might have some data. The most difficult aspect to measure is the radiated energy of the HF signal and it various components (groundwave / skywave etc). Trying to create a meaningful polar diagram of the radiated signal of a typical backstay antenna is not something many of can do.
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Old 17-02-2009, 03:35   #3
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True, but I want to know what that radiation pattern typically is compared to others. Is the backstay antenna just popular because it is convenient and relatively easy or are there others that would give a better pattern with a little more effort. If I can get enough input or enough lack of input, I might write one. It seems that such a manual would be of great value in deciding what antenna system to install and how to do it. That way we could become more knowledgeable without first having to let everyone know that we really do not have a clue I'm sure that there are lots of us that do not know how to install or replace a coax connector and detailed instructions with pictures would make them much more comfortable doing the job. I guess a book on "Radio and Antenna Installation for Dummies and Experts Alike" where all of the info is in one place would be nice.
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Old 17-02-2009, 05:17   #4
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You can find a huge amount of info in past threads on SSB antennae and installations by using the Google search function in the "Search" pull-down menu.
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Old 17-02-2009, 14:05   #5
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Originally Posted by Hal View Post
Is the backstay antenna just popular because it is convenient and relatively easy or are there others that would give a better pattern with a little more effort.
Well you could put a yagi and rotator on the top of the mast if yer really keen .

Other than that there is very little to know for a small sail boat as the possibilites are very limited.

First thing is that all the rigging which is likely grounded is mostly within 1/2 wavelength of any antenna and so will have a big affect on the antenna's radiation pattern no matter where the antenna is located. I propose that effect cannot be reliably modeled so the influence of the rig is best forgotten about as just being part of life. A vertical whip at the transom places the anteena furtherest away from the rigging but I would venture that the gains are not worth considering.

The best antenna (assuming only verticals will fit which is the case for small sail boats) is a 1/2 or 5/8 wavelength height vertical for the frequency of interest, either bottom fed or centre fed - bottom fed being by far the easiest, is frequency independant (centre fed can be frequency independant too if open wire feeders are used but open wire feeders are impractical on a sail boat) and probably the only seaworthy method.

BUT this antenna may not be optimum on higher frequencies where it becomes longer than around 5/8 to 3/4 wavelength due to low angle radiation being lost from the pattern (lower frequencies are fine, low angle radiation is not lost even if the antenna is very short for the frequency of interest - only efficiency is lost). Whether this vertical antenna is the back stay, a whip or a piece of wire on a halyard makes no difference whatsoever - they are all just bits of metal stuck up in the air. So one just wants a bit of metal up in the air that never exceeds around 5/8 to 3/4 wavelength in length for the frequencies of interest.

That is all very easy and why people try to complicate it I have no idea. I just use a bottom fed wire on a halyard to the upper spreaders, bottom just clear of the shrouds and the run of it clear of boom and sails. Despite being right close to the rig it works far better than any vertical I have had on land (my boat is metal though) - before the boat was built I experimented with verticals close in to my metal antenna tower simulating a yacht rig and that satisfied me that the arrangement would be ok to specify for the boat.

Then there is grounding - a topic which I have my own views on but avoid getting involved in on forums due to the emotive but not necessarily very scientific views many have on the subject.
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