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-   -   SSB Backstay antenna (http://www.sailnet.com/forums/gear-maintenance/61567-ssb-backstay-antenna.html)

Zanshin 01-26-2010 05:46 AM

SSB Backstay antenna
 
I am in the process of scoping and pricing a conversion for my standing rigging from standard 1x19 wire to Dynex Dux (prestretched and strengthened Dyneema braid).

I have a backstay which currently has two insulators and where the central portion is the SSB antenna. Since the new standing rigging is single-braid and non-conductive it makes a lot of sense to hide the antenna inside the hollow core.

The manufacturer of the rigging says it is possible to do, but they want to do some pull tests to see if the tensile strength of the line is significantly impacted (particularly at both antenna terminators).

All I know about SSB is that if I tune to the right frequency and press the PTT switch somebody might hear me - but that's where my knowledge ends.

I've looked around the web a bit and seen that generally the length of the wire is more important than the diameter. One HAM site indicated that a 10 guage (2.6mm diameter) cable is sufficient, but I'd like to ask here:

What is the minimum cable diameter that would be acceptable for a backstay antenna for use in the marine SSB bands?

k1vsk 01-26-2010 08:05 AM

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.
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btrayfors 01-26-2010 08:25 AM

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

Cruisingdad 01-26-2010 09:14 AM

Quote:

Originally Posted by btrayfors (Post 563789)
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

windward54 01-26-2010 10:30 AM

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.

Shortman 01-26-2010 08:47 PM

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.

Omatako 01-26-2010 09:06 PM

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.

windward54 01-26-2010 10:35 PM

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.

Zanshin 01-27-2010 04:03 AM

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.

Zanshin 01-27-2010 04:22 AM

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?


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