Attaching antenna tuner to backstay chainplate?

jim99

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Have acquired a M710 and AT-130 tuner and trying to sort out the backstay antenna.

Is there any reason why I can't simply connect the antenna tuner to the backstay chainplate and install a single insulator near the top of the backstay? Sure does simplify things for me.
 

KellysEye

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A SSB aerial must have one insulator at the bottom of the stay and one at the top, if you connect it to the chain plate then it you touch it when transmitting you will get serious shock.
 

Martin_J

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And ideally you need the feed wire spaced away from the un-insulated lower part of the backstay with 75mm standoffs.. Or you'll get more induced current in the lower part, negating the use of the insulator..

Example of standoff shown here.
http://info.yachtcom.co.uk/hf-antennas.php

To prevent stray currents around the deck of the boat, you might also consider breaking the guard rails at some point, perhaps by having the aft ends lashed at their pushpit connections rather than stainless bottle screws or pelican hooks.
 

Martin_J

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Dockhead

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You can do what you propose, but you have to be careful that no one touches the backstay when you are transmitting. I suppose a plastic tube could be put around the lower part of backstay, which would be cheaper than an insulator. I would not use a lower insulator myself

I know someone who has connected his SSB tuner directly to a shroud chainplate, with no insulator anywhere, and has good results over 20 or 30 years like that. The whole rig is his antenna, and it works.

Antennas are complicated -- it can be worth while to experiment.
 

William_H

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And ideally you need the feed wire spaced away from the un-insulated lower part of the backstay with 75mm standoffs.. Or you'll get more induced current in the lower part, negating the use of the insulator..

I don't know what that is all about. If the chain plate were well insulated and if you take steps to avoid people touching the wire giving RF burn when transmitting then should be OK. I think the bottom insulator is fitted because almost inevitably the GRP around the chain plate will wet with salty water so proving a leakage path of power to the sea. I think it a good idea to at least carry a whip antenna of some form because of the loss of HF com when dismasted. (as required by ocean racing requirements) ol'will
 

KellysEye

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>I know someone who has connected his SSB tuner directly to a shroud chainplate, with no insulator anywhere, and has good results over 20 or 30 years like that. The whole rig is his antenna, and it works.

Utter madness that means all his rig has a high voltage and if he touches it his hand will be cooked from inside to out.
 

Neeves

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It is possible to buy small long shackles with what looks like a small sheave on the clevis pin. These are, or were, focussed at insulating lifelines (so you can imagine the size). The little sheave like device was the insulation.

We had an M800 and A120 and used these insulting shackles on our backstay aerial - with total success. We secured the back stay to the insulation (I don't recall how) and then 'filled' the shackle with silicone which ensure when the backstay was loose the insulation stayed 'in place'.

I assume your requirements in the UK are similar to ours, in Oz - the vessel needs to be licensed to carry an SSB and the operator needs an SSB endorsement to their personal radio operators license.

Jonathan
 

Dockhead

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>I know someone who has connected his SSB tuner directly to a shroud chainplate, with no insulator anywhere, and has good results over 20 or 30 years like that. The whole rig is his antenna, and it works.

Utter madness that means all his rig has a high voltage and if he touches it his hand will be cooked from inside to out.

Only when transmitting.

A highly respected circumnavigator and his wife, who have lived on their boat for something like 30 years. I suppose this setup works better if you're double handed -- easier to keep everyone away from the rig when you're transmitting.

Also, remember that the voltage in a long wire antenna is much higher (like, orders of magnitude) at the top, than at the bottom -- the impedance is not constant. For a tall rig, I'm not sure it's that great a risk at hand-grabbing level.
 
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MM5AHO

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"



"Also, remember that the voltage in a long wire antenna is much higher (like, orders of magnitude) at the top, than at the bottom"

Depends on the length and the frequency. Can be high voltage at various portions, top or bottom. For example if its a half wave at the used frequency, will be high V at bottom.
 

lw395

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"



"Also, remember that the voltage in a long wire antenna is much higher (like, orders of magnitude) at the top, than at the bottom"

Depends on the length and the frequency. Can be high voltage at various portions, top or bottom. For example if its a half wave at the used frequency, will be high V at bottom.

correct.

You could have a lot of volts of RF there.

You can make all sort of junk work 'up to a point' as an aerial.
It's nice ot have something that works well and consistently, and doesn't stop working just becuase of a bit of spray or rain.
Just because somebody got away with something once doesn't mean it's a good idea to copy it.
 

Dockhead

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correct.

You could have a lot of volts of RF there.

You can make all sort of junk work 'up to a point' as an aerial.
It's nice ot have something that works well and consistently, and doesn't stop working just becuase of a bit of spray or rain.
Just because somebody got away with something once doesn't mean it's a good idea to copy it.

Of course, everyone would have to agree with that.

I was not necessarily recommending doing that; just noting that antennas are complicated and work sometimes in apparently mysterious ways.

I think what the OP has proposed -- with the upper insulator -- would be perfectly good practice if he protected the first couple of metres of the backstay from human contact. In fact I think it's better in some ways than having a lower insulator.
 

lw395

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Of course, everyone would have to agree with that.

I was not necessarily recommending doing that; just noting that antennas are complicated and work sometimes in apparently mysterious ways.

I think what the OP has proposed -- with the upper insulator -- would be perfectly good practice if he protected the first couple of metres of the backstay from human contact. In fact I think it's better in some ways than having a lower insulator.

I'd have to disagree with that.
I can't say I'm an antenna designer, but I've sorted out a few designs that don't work very well. I think it's a crap concept that would be laughed at by anyone competent in the trade. But the actual effect, you'd have to measure.
 

Dockhead

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I'd have to disagree with that.
I can't say I'm an antenna designer, but I've sorted out a few designs that don't work very well. I think it's a crap concept that would be laughed at by anyone competent in the trade. But the actual effect, you'd have to measure.

I'm curious what you think is bad about that?

I'm no antenna expert either, but this approach has been recommended to me by some very knowledgeable people.

Some obvious advantages: very clean connection below decks to the backstay; shorter run of the GTO wire, no standoff problem. So what's bad about it?
 

KellysEye

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I forgot to mention how many yachts I've seen with SSBs and two insulatorrs. 800 on theARC, over 50% of yachts the Caribbean are American and they all have SSBs, a thousand plus of them and the main European countries I saw were Scandinavian, Dutch and French 600+. So overall I've seen well over a thousand.
 
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john_morris_uk

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And ideally you need the feed wire spaced away from the un-insulated lower part of the backstay with 75mm standoffs.. Or you'll get more induced current in the lower part, negating the use of the insulator..

Example of standoff shown here.
http://info.yachtcom.co.uk/hf-antennas.php

To prevent stray currents around the deck of the boat, you might also consider breaking the guard rails at some point, perhaps by having the aft ends lashed at their pushpit connections rather than stainless bottle screws or pelican hooks.

That's exactly how I wired mine. I used cable ties and bits of plastic tube as stand off insulators. The whole thing works a treat.
 
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lw395

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I'm curious what you think is bad about that?

I'm no antenna expert either, but this approach has been recommended to me by some very knowledgeable people.

Some obvious advantages: very clean connection below decks to the backstay; shorter run of the GTO wire, no standoff problem. So what's bad about it?

If the deck is wet, you have possibility of high RF voltage meeting a body of water.
That can conduct to some extent, anything non-linear can damage your transmitter, distort the signal and create interference in other bands.
It sounds like it could be made to work well enough if you're lucky and it's done carefully, but otherwise it's asking for trouble.
If you manage to promote electrolytic corrosion of your backstay fixings or galling of the threads, I won't be surprised.
 
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