Does my antenna make sense?

[jim99]

Have acquired a used Icom SSB. Thought I would put a single insulator near the top of the backstay.

From the tuner, I will run a feed line to a bolt on the backstay chainplate, turning the entire backstay, from the tuner to the insulator, into an antenna.

I will put some sort of plastic tubing around the backstay for the 5-6 feet that might be touched by someone who is in the cockpit during transmissions.

Works for me... You?

Cheers

 

[ProDave]

To be correct you would want an insulator at the bottom as well. I guess you are arguing a chain plate bolted to fibreglass is an insulator?

 

[jim99]

To be correct you would want an insulator at the bottom as well. I guess you are arguing a chain plate bolted to fibreglass is an insulator?

No, the backstay, from the tuner to the chainplate to the insulator, would be live.

The plastic tubing would prevent electrical shock.

I'd save money with only one insulator and I would not be drilling holes in my boat.

 

[mjcoon]

No, the backstay, from the tuner to the chainplate to the insulator, would be live.

The plastic tubing would prevent electrical shock.

I'd save money with only one insulator and I would not be drilling holes in my boat.

Preventing electrical shock is good. But transmission power must not be bled off instead of radiated. I take it your boat is not aluminium or steel? Even so, chainplate fixings and backing plates are not naturally well insulated at VHF frequencies. You would not have to drill a hole in the boat to have an insulator in the backstay at a bit above reach height.

Mike.

 

[BelleSerene]

Works for me... You?

Cheers

No. Please don’t. I wouldn’t touch an insulated live HF antenna at the best of times. But with sea water, rain or dew linking the antenna to your plastic sheath, your great idea is a candidate for the Darwin Awards. And I don’t suppose you were going to calculate antenna length, or using high-voltage wire between radio and backstay?

Get someone who knows what they’re doing to do it.

 

[jim99]

You would not have to drill a hole in the boat to have an insulator in the backstay at a bit above reach height.

I would have to drill a hole in the deck to lead a feed line from the tuner to above the bottom insulator.

I have been told that there is sometimes a wonky RF link between a chainplate and the hardware at the bottom of a backstay. If that is the case I would run a wire from the bottom of the backstay to the same bolt on the chainplate that my feedline that runs from to the tuner. Again, no holes.

 

[jim99]

And I don’t suppose you were going to calculate antenna length, or using high-voltage wire between radio and backstay?

That has all been done. The antenna and control lines from the radio to the tuner are Icom standard. The tuner is a metre from the backstay chainplate. I would probably use GTO 15 from the tuner to the backstay.

 

[gertha]

The main challenge to SSB is getting a good earth.
If you are trying to save money , why not pull up a suitable Ariel wire, by spare halyard, striped of insulation, at times when you want to receive and transmit.
This saves the cost of both insulators and if prepared properly gives good protection at deck level.
Cannot think a bolt through a chain plate connected to a rigging screw connected to back stay is going to give a good connection.
However last year I failed to connect the tuner to the backstay and the tuner on its own was giving me 30 miles, so maybe a poor connection will give you all you want.

 

[jim99]

If you are trying to save money , why not pull up a suitable Ariel wire, by spare halyard, striped of insulation, at times when you want to receive and transmit.
This saves the cost of both insulators and if prepared properly gives good protection at deck level.

Good suggestions. I thought about a rope antenna, but wanted something more permanent. All our halyards are typically in use while sailing so I would be raising the antenna at anchor every time I wanted to use the SSB, as well as an all-band receiver we now have aboard.

It's not really about saving money. Just want to keep things simple with the fewest holes in the boat. Think I will push ahead and try it. Worst that can happen is it won't work (assuming I shrink wrap the backstay so no one is electrocuted).

 

[Birdseye]

Good suggestions. I thought about a rope antenna, but wanted something more permanent. All our halyards are typically in use while sailing so I would be raising the antenna at anchor every time I wanted to use the SSB, as well as an all-band receiver we now have aboard.

It's not really about saving money. Just want to keep things simple with the fewest holes in the boat. Think I will push ahead and try it. Worst that can happen is it won't work (assuming I shrink wrap the backstay so no one is electrocuted).

The reality in my experience is that you only use the SSB at anchor though I suppose it would be different if you were to do an ocean crossing. In any event, with the hoist up on a halyard approach, you get issues with the proximity of rigging wires which radically affect the swr. Its a nice idea but not a good one. Certainly didnt work well for me.

I would definitely argue against your intial proposal - salt encrusted and inevitably dirty GRP is not a good insulator. SSB transmission is dependant on both a good aerial ( the word antenna is an americanism ) and a good ground plane. The aerial needs to be at the right length for the transmission bands you intent to use or to be precise it need to avoid the wrong lengths for the bands you intend to use. If I remember 14303 is the ham maritime mobile net frequency so base on that.

I initially made the mistake on the current boat of trying to get the longest length of active backstay that I could so I put the top insulator at the end close to the mast. This had a nasty effect on the performance of the aerial and I had to relocate the insulator to a couple of meters down the wire. Presumably it was a capacitance effect against the earthed metal mast.

The biggest issue is the ground plane. I have tried numerous approaches from using the guard rail wire on a cat to a purpose designed grounding plate to bolts to my current lead keep. Never really found an entirely successful result though I once had a chat with a fellow ham in Venezuela from my boat in Spain when using the guard rails.

I played with the SSB because I am a licenced radio ham . I didnt find it much use at all, and indeed I cant remember when the set in my boat was last used. . Must be at least 2 years.

 

[Beelzebub]

If money is no object, an automatic antenna tuner and a long transom-mounted whip aerial may be the way to go. As birdseye has already stated, the groundplane is of huge importance. The mass of a decent-sized lead keel can serve such a purpose. Also, cabling of the groundplane has to be considered:- copper strip say 3" wide is a better bet than insulated wire.