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Old 31-10-2013, 05:48   #31
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Quote:
Originally Posted by transmitterdan View Post
Let's use logic: Current flows in the center conductor. The outer conductor is not connected to anything. So long as the outer conductor is short relative to a wavelength there will be no current in the outer conductor. Ohm's law says if there is no current there can be no heat and thus no loss.
Now we're talking RF. A 2.5 meter section is 1/4 wave for 28MHz and I often see 2.5m or more for wire from the tuner to the backstay, all neatly attached with spacers to keep it away from metals.

To be safe the wire should be much shorter, say 1 meter (that is 3'). Boats that use longer lengths can do better with GTO or even just AWG14 wire. I use 2' of AWG8 between tuner and vertical whip.
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Old 31-10-2013, 05:50   #32
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Re: Coax cable between SSB tuner and backstay antenna

Interesting and, at times, amusing discussion :-)

To the OP....

Bottom line: JUST ABOUT ANYTHING METALIC WILL WORK

- A length of piano wire.
- A length of coax with shield shorted at one end
- A length of coax with shield shorted at both ends
- A length of coax with shield floating
- A piece of AWG16 insulated wire
- A piece of AWG 1/0 cable
- A length of copper tape
- A length of braided ground cable
-A length of copper tubing

So why is GTO-15 recommended and widely used by most professional installers?

Simply because it makes the most sense.

- its widely available (as neon wire)
- it has 15,000 volts insulation property and will not arc, even at high power
- it has good RF conduction properties
- it tends to stand up well in the marine environment (UV, water intrusion, etc.)
- it's cheap
- it's very easy to deal with mechanically

So....kudos to all the inventive folks who use other materials for the transmission line to the antenna.

For me, I'll continue to use only GTO-15 on my boat, at my home installation (end-feeding an inverted-L wire), and on my client's boats.

Bill
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Old 31-10-2013, 05:55   #33
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hmpffff.. a transmission line connects an antenna to a transmitter. There is no transmission line between automatic tuner (antenna coupler) and antenna. The materials chosen for this length of cable/pipe/whatever become part of the antenna itself.
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Old 31-10-2013, 06:03   #34
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Re: Coax cable between SSB tuner and backstay antenna

I'm sure Bill knows that but I agree with his terminology. On most single antenna sailboat installations you have a wire antenna of some sort (most commonly a backstay with two insulators) that is fed by a wire from the tuner. Yes, both radiate RF, but one may correctly be considered a "feed" and the other the antenna. Many "feeds" can be radiating elements.

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Old 31-10-2013, 06:30   #35
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I used electric fence wire, cheap and cheerful, and bought some ignition HT wire (solid wire, not carbon core) to fit at a later stage. 8 yrs later it's still stored under a bunk!

John
GTO 15 is just ordinary wire with a greater then necessary insulation breakdown voltage , frigging bell wire would nearly do.
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Old 31-10-2013, 07:23   #36
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Re: Coax cable between SSB tuner and backstay antenna

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Originally Posted by Auspicious View Post
I hope we can agree that the best place for a tuner is dry
We have two of them located on top of our arch. Been there for 15yrs with no problems at all. Both our AT-130 and SG-230 are rated as fully waterproof.

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Old 31-10-2013, 07:32   #37
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Re: Coax cable between SSB tuner and backstay antenna

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The difference between a solid 1/2" conductor and this is the dielectricum which insulates for RF and thus creates two parallel conductors, each with different impedance. Connecting braid and core at each end and expecting same as a single conductor is a DC view, not RF. The heating loss statement was separate and for the case where the outer braid is not connected. The loss caused by the shield, small as it is, appears as heat. Losses almost always appears as heat.
The Shakespeare HF whips use several thin parallel wires around the circumference connected at the feed point. Isn't this the same concept?

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Old 31-10-2013, 07:37   #38
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Re: Coax cable between SSB tuner and backstay antenna

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Originally Posted by Auspicious View Post
Look at all the directive antenna designs with unconnected directors and reflectors. Current flows in those elements. That's why they work.
Wait - those have to be at very specific spacings and lengths and are wavelength dependent, don't they? And those spacings and lengths are at least 10X that of coax shield to conductor.

It doesn't seem relevant to me.

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Old 31-10-2013, 07:49   #39
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Re: Coax cable between SSB tuner and backstay antenna

Lot's of wrong information and opinions in this thread. For future readers go back and read post #32 by Bill (WA6CCA). It is 100% correct.
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Old 31-10-2013, 07:54   #40
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Lot's of wrong information and opinions in this thread. For future readers go back and read post #32 by Bill (WA6CCA). It is 100% correct.
Yes, and I kept reading with amusement and wondering why btrayfors (Bill) wasn't in the middle of the craziness. This is his bailey wick ....
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Old 31-10-2013, 10:34   #41
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Re: Coax cable between SSB tuner and backstay antenna

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Originally Posted by colemj View Post
We have two of them located on top of our arch. Been there for 15yrs with no problems at all. Both our AT-130 and SG-230 are rated as fully waterproof.
I just knew someone would say that. Right after I clicked Submit I remembered seeing tuners on the boat deck rail on Navy YPs.

Putting the tuner in the weather increases the importance of maintaining the ground and antenna connections. I expect you clean those up periodically Mark.

Quote:
Originally Posted by colemj View Post
Wait - those have to be at very specific spacings and lengths and are wavelength dependent, don't they? And those spacings and lengths are at least 10X that of coax shield to conductor.
To perform as desired the spacing is definitely wavelength dependent. No question. My point was (and is) that there is interaction between elements whether there is a connection or not.

I don't often disagree with Bill Trayfors. He has half again the experience I do. This is the second thing ever that I can think of where I disagree (there used to be another but I think he now uses my solution). I think he is off base suggesting that using coax between the tuner and backstay attachment is a reasonable alternative.

We're both going to be in Melbourne in three weeks, along with Scott (WA0LSS). I'm sure this will come up. *grin*
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Old 01-11-2013, 05:34   #42
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Re: Coax cable between SSB tuner and backstay antenna

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Originally Posted by Auspicious View Post
.................

I don't often disagree with Bill Trayfors. He has half again the experience I do. This is the second thing ever that I can think of where I disagree (there used to be another but I think he now uses my solution). I think he is off base suggesting that using coax between the tuner and backstay attachment is a reasonable alternative.

We're both going to be in Melbourne in three weeks, along with Scott (WA0LSS). I'm sure this will come up. *grin*
Don't believe I said that using coax was "a reasonable alternative". Rather, I said that "just about anything metalic will work". I didn't say how well it will work :-)

For most folks, my advice is "use GTO-15 and ignore all the chatter about other alternatives".

Bill
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Old 01-11-2013, 07:08   #43
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Re: Coax cable between SSB tuner and backstay antenna

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Originally Posted by btrayfors View Post
Don't believe I said that using coax was "a reasonable alternative". Rather, I said that "just about anything metalic will work". I didn't say how well it will work :-)

For most folks, my advice is "use GTO-15 and ignore all the chatter about other alternatives".
Thanks for clearing that up. On the above we can most definitely agree.
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