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Old 18-04-2011, 14:56   #16
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Re: SSB Radio

Thanks, but I'm a singlehanders, so it's not really an issue. Might even come in handy if I'm boarded... ;-)
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Old 18-04-2011, 15:27   #17
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Re: SSB Radio

Quote:
Originally Posted by smurphny View Post
I take it you are aware of the shock hazard from SSB output.

Would sliding a plastic sleeve over the lower section of the backstay where the possibility of contact comes into play prevent this issue?
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Old 18-04-2011, 15:46   #18
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Re: SSB Radio

I have twin back stays and used the old topping lift(rigid vang now) to hoist a # 14 wire to the mast head. It terminates at the stern radar (Alum)pole that has a fiberglass rod for a mount. On the rod is a 1:1 balun ground wire to the pole then wire below deck from pole to a thru hall fitting. Stern push pit is also tied in, Works like a champ. I am on 20 and 17 meters most weekends. I have talked to NV, NM, IL, NY,socal and northern Minn from PDX. Alinco dx-70 and LDG z100 tuner.
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Old 18-04-2011, 15:49   #19
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Re: SSB Radio

The "shock hazard" of HF radios is WAY overblown, in my experience (40+ years). If we were using 1,500 watt radios in lieu of the 100-150 watt radios typical on cruising boats, I'd be more concerned.

And, yes, if you're really worried about it slip a PVC boot over the lower 7-8'.

BTW, the antenna begins AT THE TUNER (usually belowdecks), and a long run of GTO-15 feedline to a spring stay isn't particularly efficient. It'll work and it'll tune, but then so will almost anything connected to the very capable Icom and SGC tuners found on most boats.

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Old 18-04-2011, 15:57   #20
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Re: SSB Radio

BTW, the antenna begins AT THE TUNER (usually belowdecks), and a long run of GTO-15 feedline to a spring stay isn't particularly efficient. It'll work and it'll tune, but then so will almost anything connected to the very capable Icom and SGC tuners found on most boats.

Bill
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So if I understand you correctly Bill I will be better off attaching the GTO closer to the cockpit, rather than 20 feet up the stay?

If all it takes is a PVC sleeve on the lower section why would anyone insulate the backstay, has this been a marketing ploy to sell high priced
products all these years?
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Old 18-04-2011, 16:24   #21
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Re: SSB Radio

[/Quote] So if I understand you correctly Bill I will be better off attaching the GTO closer to the cockpit, rather than 20 feet up the stay? [/QUOTE]

Yes, absolutely.

[/Quote] If all it takes is a PVC sleeve on the lower section why would anyone insulate the backstay, has this been a marketing ploy to sell high priced products all these years?[/QUOTE]

No, not just that. It's most likely a holdover from the practice on large ships where much more powerful transmitters are used, and because of liability concerns. I've never heard of anyone being burned on a sailboat by grabbing an unprotected backstay. If you were to grab one while someone was actually transmitting -- not just listening -- you might well feel a tingle and you'd certainly remove your hand fast unless you were brain dead. For most cruising boats, this is just not a real concern. Happily, since it means you can get better efficiencies by either feeding the backstay or shroud from the chainplates belowdecks, or installing an insulator not far above decks.

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Old 18-04-2011, 16:26   #22
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Re: SSB Radio

The HF tech that worked on my boat said a horizontal antenna would be better than a vertical one, that's why the spring stay. He could be wrong I guess.
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Old 18-04-2011, 16:31   #23
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Re: SSB Radio

No, not just that. It's most likely a holdover from the practice on large ships where much more powerful transmitters are used, and because of liability concerns. I've never heard of anyone being burned on a sailboat by grabbing an unprotected backstay. If you were to grab one while someone was actually transmitting -- not just listening -- you might well feel a tingle and you'd certainly remove your hand fast unless you were brain dead. For most cruising boats, this is just not a real concern. Happily, since it means you can get better efficiencies by either feeding the backstay or shroud from the chainplates belowdecks, or installing an insulator not far above decks.

Bill[/QUOTE]

Considering I am getting ready to cut a new backstay as we speak its great to know that I can save hundreds on new insulators and have less chance for failure. I like the idea of the PVC sleeve, will run that maybe 10' feet above cockpit to the boomkin and tie the GTO right above the sleeve. Does the PVC have any negative effect on the antenna efficiency?
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Old 18-04-2011, 17:34   #24
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Re: SSB Radio

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If you were to grab one while someone was actually transmitting -- not just listening -- you might well feel a tingle and you'd certainly remove your hand fast unless you were brain dead.
This is really interesting. My tuner is located just below the aft deck, about one foot from the aft chainplate. It sure would be nice to simply run a wire and get rid of the split lead antenna altogether and stow it for emergency use. I have some leftover 1/4" lifeline cover that would slide right over the stay nicely. If it's really true that there is not enough amperage to hurt someone getting between the transmit current and ground, this would be the way to go. Does anyone have an idea about the actual amperage produced when transmitting. It does not take all that much to give you a hell of a shock. 1a at 110v will kill you in water.
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Old 18-04-2011, 19:45   #25
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Re: SSB Radio

If your backstay is ungrounded at the lower end (chainplate), and you aren't using a lower insulator, there is no need to run GTO-15 some distance up the backstay to feed it - you should feed it as low as possible with as short a run of GTO-15 as you can. Viking Sailor (Paul) runs his GTO-15 up because his backstay IS grounded at the chainplate and he has to use what is called a "shunt feed" technique for it to work well.
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Old 18-04-2011, 21:14   #26
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Re: SSB Radio

smurphny -

High voltage, high current RF will burn but not kill like 120v 60Hz because RF frequency is so high that current flow reverses before nerve and muscle (heart muscle) can be "paralyzed" in one direction, so to speak.

RF (over 100 kHz) is routinely used in the operating room to cauterize and cut at power levels very similar to what our marine and ham radios are capable of putting out. When the energy is concentrated at the tip of a probe, it can burn and cut tissue very easily. If you happen to grab a transmitting antenna with your hand, the current is more widely distributed and the effect a bit less dramatic, even if you are grounded.
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Old 18-04-2011, 21:29   #27
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Re: SSB Radio

Much speculation on the danger and no facts. Typical for a forum. One of you engineers should go put you feet in the sea and grab the SSB antenna while someone runs Sailmail on various wavelengths. Report back if you can. Until then I'm sticking with the tried and true.

Cheaper insulators are the utility-pole-like ceramic units that the backstay wire loops thru. Failsafe. Common in the old days.
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Old 19-04-2011, 03:51   #28
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Re: SSB Radio

Bill is right when he says it isn't really an issue.

As for actual voltages, it is a bit meaningless to quote them as the voltage level will vary from say 0 through to possibly several thousand volts along the length of the antenna depending on (among other things), the frequency.

So at one frequency, the voltage say at hand height on the antenna might be only a few volts while at another frequency, it may be in the order of hundreds if not a thousand or so volts.

Even so, as Bill mentioned, given a Tx power of less than 150 watts, the actual effect is unlikely to be more than a tingle or a small burn at the worst at the entry / exit points. One would soon let go anyhow.
Don't sweat the small stuff.
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