For all practical purposes, there is no min diameter. However, there is interaction between materials in close proximity to any antenna regardless of whether or how conductive the proximate material may be. I have seen this problem occur in many varied applications over the years installing, maintaining and operating antennas and would suggest that you consider something similar to a GAP antenna or it's equivalent which can be found with a simple Google search.

There are lots of alternatives which work more effectively than the GAP antenna as well but that discussion is beyond the scope of your question so I'll stop there.

Opinions are numerous and any generic statements usually have exceptions but all I can tell you is my own experience to not try what you described.

 

I agree with Don (K1VSK).

One very good alternative: an "alternate backstay" antenna, made of s/s lifeline. Lots of posts on these here, on CruisersForum, and the SSCA Board.

Bill
WA6CCA

 

That is what I am going to do too. As Bill once said to me, why cut a perfectly good backstay!??

Brian

 

I don't think I have ever seen a minimum cable diameter ever specified. The insulator usually is the limiting factor as they are only made in set sizes.

 

There is an interesting note on SSB antennas in the current issue of Sail by Gordon West. BoatWorks Ask Sail p.87. References GAM/McKim antennas that don't need an insulated backstay, the use of a whip antenna, or running a GTO-15 cable inside a double braid sheath & hoisting up the mast when you need.
It is not online yet. Just got it in the mail.

 

There is an interesting note on SSB antennas in the current issue of Sail by Gordon West. BoatWorks Ask Sail p.87. References GAM/McKim antennas that don't need an insulated backstay, the use of a whip antenna, or running a GTO-15 cable inside a double braid sheath & hoisting up the mast when you need.
It is not online yet. Just got it in the mail.

G. West says in this note that the Gam/McKim antenna "is a nice alternative for temporary installations". In my mind this translates to "not as good as a typical insulated backstay installation". Any thoughts on why he might use the word 'temporary'.

 

Information on the GAM antenna is available on their own website.

Gam Antennas

I have one on my boat and think it is a good solution. With this antenna my SSB works as well as any I've tried. The concept of cutting my back-stay doesn't sit well with me.

I have no commercial interest in the product - just a satisfied user.

 

I had a Gam antenna on my boat until recently. I ran into an issue with the GTO-15 wicking up moisture. The GTO-15 corroded and I had to send the antenna back just to get it replaced. Not a great option when you are out and away from the dock on an extended trip. And I'm not the only one that I heard of with this issue.

Two comments to be fair. First, the antenna worked just the way it was advertised. It worked just as good as my new backstay antenna. Second, the customer service was outstanding. They fixed and returned the antenna within 10 days. As long as you have a single backstay, the antenna is easy to install.

 

The GAM Antenna looks very interesting, but with 2 cores it wouldn't fit inside my intended backstay; I'll see if I can find a copy of SAIL here in Europe when that issue gets published and distributed.

 

K1VSK - what sort of interactions are you referring to? If I were to embed an antenna into the nonconductive Dyneema, could you envision that the structural integrity might suffer over time? Dyeema doesn't like temperatures of over 150C, could those be reached somehow when transmitting?

 

The most common form of interaction is parasitic and takes the form of effectively changing both the impedance and electrical wavelength of the antenna. This is a lot more complex set of interactions than is worth going into here but hopefully it will suffice to say that in erecting various forms of antennas over the years, we have found that virtually any material in close proximity to an antenna has an effect.
You will not find any measurable temperature change.

 

Zan,

I merged them. You can go back and delete any duplicate posts now, if you feel like it.

 

I scanned the article. I am home with a yucky cold, so I have the time. But I have never had luck posting photos here. It is a jpg 87k, meets requirements. There was a post once about the vodoo req'd to post, but I cannot find it.

 

If this is a direct repro of copyrighted material, you can not verbatim paste it here. Sorry. I have no problem with you linking it, but copyrighted material is, well, copyrighted for that very purpose.

Sorry.

Brian

 

OK gotcha

 

I found a page on the web showing physical characteristics of Dyneema and they stressed that it makes an optimal covering for radar and sonar as its dielectric constant is a low 22oC/10GHz: 2.25 and Loss tangen: 2. 10-4 {which means nothing to me, but sounds impressive} so perhaps that is a point in its favor if used around a SSB antenna.

Here is the link to the manufacturer's factsheet: http://www.dyneema.com/en_US/public...S/public/dyneema/downloads/Comprehensive_factsheet_UHMWPE.pdf?DCSext.src=search

 

Zanshin, I'm not aware of any numbers for longwire antennas, but in general IIRC as the antenna "tubing" gets thicker, the antenna can work a wider frequency range with lower SWR.

I'm probably getting something not-quite-right with that description, but for conventional antennas thicker tubing has definite advantages, and the same physics behind it would tend to indicate a thicker wire for wire antennas might also have some real benefit. (Aside from being thick enough to carry power without heat damage.)

Something you might want to check into.

 

Julie, I think I have heard Mr. West comment on this antenna before, some years ago. The antenna is nothing new or magical, and Mr. West sometimes says more than what he is saying, or just what he is saying, if you read between the lines.

As I recall it, he said the antenna was very well made, that he had in fact used one, and that's important because no antenna works well if it takes water damage, etc. But he did not make any comment or judgement about comparable performance or price, and to "read" more about that you only need to know basic antenna design theory. He doesn't do Consumer Reports type comparisons.<G>

There's no $400 worth of antenna there, nicely jacketed and insulated and able to be taken down and moved and raised repeatedly and still work as well as it does on day one. Unless you figure, someone has to pay for low volume hand production, distribution, and retail market, as usual.

You could build the equivalent by trimming some wires yourself for a fraction of the cost, or you could probably outperform it with a permanent installation tuned to your preferred frequencies and matched to your rigging. No matter what antenna you use, the rigging that is unique to your boat will uniquely affect performance and make it extremely difficult for any "one size fits all" solution to work as well on any two different boats.

Antennas all share the same physics, anything that works by "magic" or that isn't described in conventional terms by antenna type and theory, probably is all sizzle and no steak.

But, for the folks who don't want to crunch the numbers and solder the wires...sometimes a well-made "average" performer is still the right product. Sometimes "reliable" is worth having.