Using standing rigging as a short wave antenna

[ndavie]

When the feed wire is a coax, and tuned to have low swr, the feed wire does not radiate much. Need to have a decent ground, of course.

[Franziska]

Thanks again.

So feeder coax, well grounded.
Feeder up until well over deck.
Antenna tinned wire with insulation in marine quality.

Alternatively as per Jim the whole rig.

For now the base is set :-)

[transmitterdan]

No, there should be no coax at the output of the tuner. This will make it harder for the tuner to work and will reduce radiation efficiency. Reread Paul Elliot's post.

Franziska,

I would be reluctant to put a SSB transmit wire inside a piece of single braid standing rigging. The reason is the single braid can be damaged either by lightning or by the SSB transmitter itself. The voltage at the top of a wire antenna can be very high during transmit. Especially on lower frequencies and at high frequencies where the wire is exactly a quarter wave long. Without proper treatment at the top there can be corona inside the single braid that damages the fibers. I would strongly recommend against this idea. You can use a halyard to raise a wire antenna to an upper spreader (or lower depending on rig height). If that halyard fails the rig is not in jeopardy.

[waterman46]

Originally Posted by Jim Cate

But, as i have often posted in threads like this one (and they come up very frequently) we've used the entire rig... mast and all rigging... as an uninsulated antenna for many years. We have done it with the base of the mast grounded and with it isolated, and it works well either way. It may not be ideal, but it works as well as insulated backstays as far as signal reports from distant stations can determine.
Jim

Jim, I think it would interest many if you could provide a few details of your HF antenna configuration. Such as, how or where you connected the tuner to the boats rigging, also is your mast stepped on deck or keel, and are spreaders wood or aluminum? Thanks!

Doug

[Jim Cate]

Originally Posted by waterman46

Jim, I think it would interest many if you could provide a few details of your HF antenna configuration. Such as, how or where you connected the tuner to the boats rigging, also is your mast stepped on deck or keel, and are spreaders wood or aluminum? Thanks!

Doug

G'Day Doug,

OK, the attachment is via the chainplate, which is about a meter from the tuner (manual MFJ Versatuner II). Mast is "keel" stepped, but in our strip planked timber boat, that means the step sits upon a massive timber structure, so it is not inherently grounded there. I've tried it both bonded to the steel shell keel and isolated... the tuning changes but no readily observable change in signal strength was reported. (That is not a very scientific comparison and far from complete, so there may be differences in radiation patterns). There are two sets of swept back spreaders and they are alloy.

The backstay does have insulators, btw, so it is isolated from the rest of the rig. Following a suggestion from someone here on CF I ran coax up the mast and set the backstay up as a top fed sloper... great performance was promised and I was keen to try it out. What I've found is that on 40 meters (the band I most often use) it is a great rx antenna with very low noise, but consistently 2 or 3 s units lower reports from distant stations. Works pretty well on 20, and when in noisy locations I sometimes use it on that band.

Anyhow, several friends have used the whole rig on their boats with good results, no one has been shocked or gotten RF burns, and they have been happy with the simplicity of the system. No guarantee for anyone's outcome, but it is a simple and inexpensive thing to try out.

Jim

[waterman46]

Originally Posted by Jim Cate

G'Day Doug,

OK, the attachment is via the chainplate, which is about a meter from the tuner (manual MFJ Versatuner II). Mast is "keel" stepped, but in our strip planked timber boat, that means the step sits upon a massive timber structure, so it is not inherently grounded there. I've tried it both bonded to the steel shell keel and isolated... the tuning changes but no readily observable change in signal strength was reported. (That is not a very scientific comparison and far from complete, so there may be differences in radiation patterns). There are two sets of swept back spreaders and they are alloy.

The backstay does have insulators, btw, so it is isolated from the rest of the rig. Following a suggestion from someone here on CF I ran coax up the mast and set the backstay up as a top fed sloper... great performance was promised and I was keen to try it out. What I've found is that on 40 meters (the band I most often use) it is a great rx antenna with very low noise, but consistently 2 or 3 s units lower reports from distant stations. Works pretty well on 20, and when in noisy locations I sometimes use it on that band.

Anyhow, several friends have used the whole rig on their boats with good results, no one has been shocked or gotten RF burns, and they have been happy with the simplicity of the system. No guarantee for anyone's outcome, but it is a simple and inexpensive thing to try out.

Jim

I may have missed something in this thread. Dumb question: The chainplate you are connecting to, is it the upper shroud, or the backstay? When chainplates are mentioned I think, mistakenly, only of shrouds.

[Jim Cate]

Originally Posted by waterman46

I may have missed something in this thread. Dumb question: The chainplate you are connecting to, is it the upper shroud, or the backstay? When chainplates are mentioned I think, mistakenly, only of shrouds.

We have but one shroud chainplate each side, and this is the one on the port side (with this swept back rig, the caps, intermediates and lowers all terminate at the same place).

I don't know if it matters much where you feed the mess... on our previous boat (old IOR one-tonner) we fed via the backstay chainplate and that worked too.

Jim

[continuouswave]

Originally Posted by Paul Elliott

Very true, but there's no reason we should necessarily desire a dipole pattern.

Yes, that may be true, but I am afraid it was the OP who asked for a "dipole" antenna to be created. As I explained to him, he is not going to get a dipole radiation pattern out of his random collection of wires across the entire spectrum of 3 to 30-MHz.

[Paul Elliott]

Originally Posted by continuouswave

Yes, that may be true, but I am afraid it was the OP who asked for a "dipole" antenna to be created. As I explained to him, he is not going to get a dipole radiation pattern out of his random collection of wires across the entire spectrum of 3 to 30-MHz.

Yes, and my comment wasn't a dig at you. I assumed that the OP was less concerned with the "dipole" part than the "antenna" part. and just wanted to point out that there's nothing magic about the dipole radiation pattern.

[David B]

Originally Posted by continuouswave

There is really no antenna known as an inverted dipole. The term "dipole" refers to the radiation pattern of the antenna, not to a particular form of the antenna. The most common form of antenna with a dipole radiation pattern is a half-wavelength horizontally polarized linear antenna fed in the center. If the legs of the antenna droop, this is often called an inverted-vee half-wavelength antenna.

There is no expectation and no reasonable basis for a jumble of random length rigging wires, a mast, and other conductors all bonded together to exhibit a dipole radiation pattern across the 3 to 30-MHz spectrum.

Probably means an Inverted V antenna. That is definitely a dipole. Centre-fed, with feed-point the highest, and the ends down towards ground (deck) level.

[David B]

Originally Posted by Franziska

One question, I'm replacing standing spectra rigging.

Now would be a good moment to put a wire in the core to be used later for Short Wave Radio.

What kind if wire should I put in?
Coax? Tinned? Stranded?
What length should I put in?
What diameter?

As stated above its just to prepare a possible later marine short wave radio installation at a convenient point in time.
I am aware that later there will be more stuff to do, like a ground plate and the like...

Thanks for suggestions.

Yes, good idea. Copper (not hard-drawn, but regular soft, stranded copper - preferably tinned, with good insulation) would be ideal. Beware also, the end - at certain frequency/antenna length combinations, very high voltages can appear at the far end. So think arcing, and spectra and standing rigging supporting a mast ......
Make sure the end is very well insulated. Cut the wire to length, plus a few cm. Work the insulation back as far as you can. Trim the copper to the length you want, then work the insulation back over it. Now fold the empty insulation over, and slip some heat-shrink sleeving over it. Shrink it, then a final layer of glue-lined heatshrink sleeving over the end will give you a water-proof, and hopefully arc-proof termination.

As to diameter, the theory is the larger the better, but you need to get it up inside the core, so that is a big limiting factor. 2.5mm2 would be the minimum - 4mm2 would be better.

Down the other end, if you have the wire exiting the spectra above head-height, then joined to a heavier insulated wire running outside the spectra, then down through a gland to your ATU, that will give protection for crew, but frankly, no one should be near the conductor when you are transmitting anyway.
Finally, the other option is to have a separate length of copper-cored double braid. That way it is fully independent of your rigging.

Length - depends on the frequencies you intend using.

Hope that helps.

David

[cburger]

My backstay has been pretty good at receiving signals. The new Icom as a dedicated receiver has been much simpler, faster to operate for tuning than the old push button Sea. The idea behind my question was to judge if a different length longer, with a different shape may improve reception.
The Icom RC75 will allow the use of two antennas, coax and long wire.

Last weekend I attempted to attach the lower shroud by running copper wire to a thru bolt from the chain plate inside a locker with no result.

[cburger]

Picture of the installation