Backstay insulation for SSB

[Posse]

Would you consider this to be sufficient insulation for the lower part of the backstay, or will I need to install an insulator?

There will be an insulator in the top of course.

[btrayfors]

Originally Posted by Posse

Would you consider this to be sufficient insulation for the lower part of the backstay, or will I need to install an insulator?

There will be an insulator in the top of course.

I don't see any sort of insulator in the pic. I believe you'll need to install a real insulator just above the block fitting.

Bill
WA6CCA

[Boatguy30]

First of all, how do you run the lead wire and still have an operational cascade tackle?

Second, what are the bearings in the block made of? If they are composite they may not conduct electricity

[Posse]

I was thinking that the block is probably not metallic, so will isolate in itself. But I may be wrong. I am not sure about the materials.

Also, I am unsure if this insulation is sufficient for HF, given that the metal parts are very close.

I was thinking to run the lead wire along one side of the lower part of the stay, but have not thought through how to make it flexible enough for operation.

There will be a targa arch behind the backstay - perhaps I can use that for routing the lead wire somehow.

[S/V Illusion]

Do you have a voltmeter? If so, check continuity. If none, the parasitic effect won't change simply by adding an insulator so it would be superfluous.

[svHyLyte]

Originally Posted by Posse

Would you consider this to be sufficient insulation for the lower part of the backstay, or will I need to install an insulator?

There will be an insulator in the top of course.

Ignoring for a moment your original question, that arrangement for a back-stay is very poor. If the line on the block at the bottom of the stay goes slack or ruptures, while under sail, unless you've got runners rigged, the mast will be toast. I suspect that was originally a split back-stay arrangement that someone (you?) wanted to make adjustable. The best way of doing that, but insuring the integrity of the rig, is to use two "cable" blocks (blocks with aluminum sheaves matched to the diameter of the cable), one each on each of the fixed length lower legs of the stay. The cable blocks are connected together and to a third block with a line running through it that is affixed at one end at one of the lower chain-plates and connected to a 2 or 3 part tackle fitted with a cam-cleat on the other end, affixed at the opposite chain-plate. One adjusts the tension on the back stay by taking a load on the multi-part tackle which pulls the 3-block arrangement downward along the line of the upper back stay, which, in-turn, draws the split lower legs of the stay together and accordingly tightening the back-stay.

With such an arrangement, one leads the antenna feed cable up one of the lower legs of the back stay, with proper stand-offs, and attaches it to the upper portion of the back-stay, above a proper insulator, leaving a bit of a loop/slack to account for the shortening/lengthening of the stay.

We had the foregoing arrangement on our prior yacht and it worked quite well with no risk of loosing the stay/mast.

FWIW...

[Boatguy30]

Actually the wire cascade as pictured is commonly used on boaters larger than the split system you describe. I've seen it used on vessels as large as 80' or so. Perfectly fine if well engineered.

[svHyLyte]

Originally Posted by Boatguy30

Actually the wire cascade as pictured is commonly used on boaters larger than the split system you describe. I've seen it used on vessels as large as 80' or so. Perfectly fine if well engineered.

So have I. But never on boats without runners rigged as I mentioned in my original comment:

...If the line on the block at the bottom of the stay goes slack or ruptures, while under sail, unless you've got runners rigged, the mast will be toast....

[Boatguy30]

I believe some of the larger Hanse use it and many other with no runners. It's sorta irrevelant since if the backstay suddenly blew with the runner on the tip of the mast would invert and quite possibly still break

[alley]

A backstay relies on an antenna tuner (i.e. impedance matching circuit) to make them resonant at the frequency of interest. Because the antenna tuner is really an impedance transformer, you can see some pretty high RF voltages at the ends of the radiating element, so you'll need some substantial insulation to keep the RF energy where you want it.

That said, from the photo it wasn't clear to me whether it was a wire or some high-tech fiber line going through the sheave. If wire, you definitely do not have sufficient insulation. If it's a fiber line, it might be OK when it's dry, but soak it with some salt water and you have a different story. Again, I think you need an insulator for it.

Mechanical rigging arguments aside, the backstay load will be carried by the bearings or bushings on the sheave. If they're metallic, I would be concerned over any potential corrosion that might be induced by RF currents and any weakening the that could result over time.

Just my thoughts and opinions. Remember, they're free and worth every cent!

Tom, KD2VH

PS - Rereading this after posting, it occurred to me that if you get corrosion on the sheave anyplace and you're using it as an insulator, the junction between the rust and metal can act as a rectifier and create a lot of noise, both on transmit and receive. Another reason to use insulators designed for the task at hand.

[donradcliffe]

As pointed out, you may want to run another fixed safety line from one side up past the block to guard against failure of the block or the adjusting line.

Don't ask me how I know this.

The fiber line will be more than sufficient insulation.

[Posse]

Thanks for all the good input.

I just applied a multimeter on the block fitting, and there is no continuity between the upper and lower part. Both the upper and lower part is wire.

However, you may be right that it is not good enough for high voltage / HF, and could have a corrosion issue. In that case, no doubt an insulator is needed.

The backstay arrangement is completely standard on this boat (Bavaria 42 Cruiser). But the block fitting may need an upgrade before ocean cruising. Possibly also some kind of backup as you mention.

Regarding the lead cable, I guess a little slack on the cable will provide enough room to adjust the backstay.

[S/V Illusion]

Originally Posted by Posse

Thanks for all the good input.

I just applied a multimeter on the block fitting, and there is no continuity between the upper and lower part. Both the upper and lower part is wire.

However, you may be right that it is not good enough for high voltage / HF, and could have a corrosion issue. In that case, no doubt an insulator is needed.

The backstay arrangement is completely standard on this boat (Bavaria 42 Cruiser). But the block fitting may need an upgrade before ocean cruising. Possibly also some kind of backup as you mention.

Regarding the lead cable, I guess a little slack on the cable will provide enough room to adjust the backstay.

No continuity means you are looking for a solution to a problem which doesn't exist.

And generalities about where along an antenna the high voltage point are stated above, it's essentially a random wire configuration in which the highest voltage is typically at the end, not the feedpoint.
That is why many people only use an insulator at the top.

[alley]

Originally Posted by Posse

I just applied a multimeter on the block fitting, and there is no continuity between the upper and lower part. Both the upper and lower part is wire.

Keep in mind that the multimeter will measure DC continuity, not RF continuity. RF will pass right through a capacitor, whereas DC will be blocked by it (open circuit).

[Posse]

I would rather say that I am seeking confirmation if lack of DC continuity is sufficient. It appears opinions are split on this question.

I can add that the distance between the closest metal parts of the upper and lower part is about 5-6 mm.