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Old 21-08-2013, 01:31   #16
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Re: Insulating BackStays for SSb antena cable

That is indeed another good solution.

I had understood that you already had the typical 2 isolators in your backstay.

If that is the case, you will of course have to bridge it around the lower isolator to use the backstay untill the chainplate as antenna wire.

If that is not the case, using the backstay untill the chainplate is OK. Bear in mind that when you connect (inside/underdecks), the stretch of wire between your chainplate bolt and the antenna tuner is also part of the antenna, and it is a high voltage part of the antenna system. And here...good practice mandates to keep it as short as possible and again lead it to the ATU away from metal (other wires, metal hardware, ...) e.g. keep it just below the GRP of the deck and/or...lead it neatly to the atu via some isolated standoffs!
Having the antenna tuner inside just at that chainplate bolt would be super.

Good works,

Jan
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Old 22-12-2013, 19:20   #17
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Re: Insulating BackStays for SSb antena cable

I have a backstay with an insulator near the top of the backstay, but no insulator at the bottom of the backstay on one side(it is a split backstay system), but on the other side, there is an insulator. Is it practical to attach the antenna tuner to the chain plate and use it as an antenna that way? What would water on the deck do to the signal when transmitting?
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Old 22-12-2013, 21:48   #18
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Re: Insulating BackStays for SSb antena cable

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Originally Posted by roverhi View Post
If your stay is insulated, all you need to do is tape the feed wire between your tuner and the insulated part of the stay to the backstay. On two boats, have done this and have had no problems getting out. Stand offs aren't needed. Don't need coax to run from the tuner to the insulated/antenna part of the backstay. Use GTO 15 insulated cable.

If I had to do it again, would only put an insulator near the mast head. No bottom insulator needed on an FRP boat. Run the feed wire from the tuner to the backstay at the turnbuckle. As long as the backstay is not bonded via the chainplate to the boat, the antenna will work fine. Just warn everyone not to hang on to the backstay while you are transmitting. Even then, doubt that anyone hanging onto the backstay would suffer much ill effect from RF energy. I'll stand by while the tin foil hat crowd has fun with this.
I did the same thing on our previous boat, a Lord Nelson when we cruised Mexico. I got good signal reports all the time with no problems at all, and I repeated the installation on our Dragonfly trimaran.
I've even demonstrated to non believers by hanging onto the shroud when someone transmits. 80, 40 and 20 meters. No shock.
Recently, the CF crowd really smacked me around on another similar thread for doing the same thing.
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Old 22-12-2013, 22:05   #19
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Re: Insulating BackStays for SSb antena cable

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Originally Posted by senormechanico View Post
I did the same thing on our previous boat, a Lord Nelson when we cruised Mexico. I got good signal reports all the time with no problems at all, and I repeated the installation on our Dragonfly trimaran.
I've even demonstrated to non believers by hanging onto the shroud when someone transmits. 80, 40 and 20 meters. No shock.
Recently, the CF crowd really smacked me around on another similar thread for doing the same thing.
Here's another smack! Different frequency, different antenna length, and you could very well have received a shock. It shouldn't be enough to kill you though, so carry on if you like -- apparently with your configuration the voltages aren't high enough.
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Old 22-12-2013, 22:21   #20
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Re: Insulating BackStays for SSb antena cable

It's not an electrical shock to be worried about but the concern would be an RF burn. 150 watts could give you a nice burn.
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Old 22-12-2013, 23:55   #21
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Re: Insulating BackStays for SSb antena cable

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It's not an electrical shock to be worried about but the concern would be an RF burn. 150 watts could give you a nice burn.
An RF burn is just a particular type of electrical shock. And yes, 150W could do serious damage. RF burns tend to cook the tissue rather deeply, or so I am told.

The voltage on a half-wave node of a backstay antenna can be several thousand volts. If this node is located where you can touch it you will get shocked. If you have a 40ft backstay antenna, when operating at 8MHz or higher, there will be a half-wave node somewhere on that backstay.
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Old 23-12-2013, 00:42   #22
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Re: Insulating BackStays for SSb antena cable

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Originally Posted by sailordiver View Post
I have a backstay with an insulator near the top of the backstay, but no insulator at the bottom of the backstay on one side(it is a split backstay system), but on the other side, there is an insulator. Is it practical to attach the antenna tuner to the chain plate and use it as an antenna that way? What would water on the deck do to the signal when transmitting?
What I suggest is that you connect both chain plates and the ground lug of the antenna tuner to a good RF ground. Then connect from the top of the lower insulator to the output of your antenna tuner. Add turnbuckle covers and slip on (split) insulation to the part of the backstay that is uninsulated and reachable from the deck. This antenna is know as a grounded shunt feed vertical.

Paul

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Old 23-12-2013, 02:02   #23
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Re: Insulating BackStays for SSb antena cable

Paul Vining sailor,

please explain again how that works?

Jan
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Old 23-12-2013, 02:08   #24
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Re: Insulating BackStays for SSb antena cable

Paul,

SHUNT FED VERTICAL

quite a different thing.

What about the gamma or Omega matching stub?

Jan
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Old 23-12-2013, 11:17   #25
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Re: Insulating BackStays for SSb antena cable

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Paul,

SHUNT FED VERTICAL

quite a different thing.

What about the gamma or Omega matching stub?

Jan
Agreed. A shunt-fed vertical has no lower insulator. The connection Vining proposed is still an end-fed vertical.

As long as the hull isn't waterlogged in the chainplate area, feeding the backstay at the chainplate should work fine. You still want an upper insulator (although the antenna might work fine without it -- it depends on the length, frequency, and tuner). With sailordiver's split backstay (one lower insulator) this should work as well. In fact, the one lower insulator may not be needed either.

Gamma and Omega matching tends to be quite frequency-sensitive. You could certainly match to a grounded backstay, but the match would only be good for a fairly narrow frequency band. I think an antenna tuner feeding a non-grounded backstay will be more likely to work.
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