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Old 26-10-2012, 03:07   #1
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Shroud as SSB Antenna?

The backstay on my boat is too fat -- 16mm or 5/8" -- to use as an antenna. There are insulators available in this size, but they cost more than $1,000 each [:eek]. Besides that, like others, I don't want to introduce additional failure points in this part of the rigging.

My boat has three spreaders and discontinuous rigging. How about if I used a shroud? The cap shrouds and lowers are also 16mm , but I've got a nice intermediate V1/D2 which is 10mm, and 12 meters long. That's about 40 feet long and a diameter where insulators are not prohibitively expensive. This part of the rigging is massively redundant and probably not highly stressed so I wouldn't worry about the structural issue.

My V1/D2 intermediates run through only the lowest spreader, and terminate below the second spreader. I realize I will have to insulate the shroud from the spreader it runs through (how to do that?). But I have another question -- the shroud makes a bend as it goes through the lowest spreader -- will that affect its efficiency as an antenna?

What do you guys think about this setup? (Paging Bill Trayfors!)

Another benefit to this setup is that the shroud chainplates are only a couple of meters from my nav table, instead of 20+ feet in the case of the backstay.
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Old 26-10-2012, 03:52   #2
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Re: Shroud as SSB Antenna?

G'Day Dockhead,

I always cringe before I post this technique. For 26 years now, on two different boats I have used NO insulators other than the hull. Currently I have a manual tuner, less than 1 metre of "feed line" to a bolt on my shroud chainplate. This makes a random length wire antenna which includes the mast and all the rigging above the deck.

It is sorta crude, but it works. Years of comparative tests show that it gets out about the same as conventional backstay antennas. Seems to be less directional than backstays, and certainly doesn't put weak points in any wires.

Why do I cringe? Because usually someone leaps on me with some sort of vile criticism! Anyhow, it does work...

Having said that, I just restepped my mast after a bit of a refit. My backstay has had insulators in it since I bought this boat (its just a light stay to induce mast bend in our fractional rig), and I've never used that wire as an antenna. But after reading of the virtues of a top-fed sloper, I'm gonna give one a try, and have led the appropriate coax to the masthead. If you are interested, I'll post my opinions after giving it a try. Will be a few days before it gets fully wired up, though... don't know what your time schedule is.

Cheers,

Jim N9GFT/ VK4GFT
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Old 26-10-2012, 04:17   #3
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Re: Shroud as SSB Antenna?

Jim the top-fed sloper is ok as a single band antenna.
If you are going to tune that antenna system belowdecks at the coax leading down you will have tremendous losses in your coax if you want to work multiband.

Jan
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Old 26-10-2012, 04:28   #4
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Re: Shroud as SSB Antenna?

Well, I suppose I could put an insulator just at the top of my backstay. Now that I think about it, the chainplate is bolted to a GRP and plywood beam, so shouldn't conduct to anything. That's one instead of two weak points, and $1000 instead of $2000 in insulators -- a little better already.

But what about the shroud idea??
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Old 26-10-2012, 04:57   #5
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Re: Shroud as SSB Antenna?

To me it doesn't sound as a good idea to try and use the shrouds though I have seen it installed on some boats:
- close and quite parallel to the mast all the way
- going through 3 spreaders you will need it well isolated

I would go for a far cheaper and flexible solution - indeed the "Bill B. Trayfors"-way with a sloping wire
- 1 (cheap) isolator at the top, and leading down to either side of the stern, attach it for instance the SB or port side of the pulpit with another isolator, from there some feet of GTO-15 down to a through-deck connector.
- just belowdecks have the ATU (automatic tuner); from there no problem at all to have 20 feet of good quality coax to you nav station.
- you will of course need an RF-ground system. Hundreds of liters of electronic ink have flown on that subject here....

No need for expensive backstay isolators.
Flexible because you can easily change the wire length to choose optimal frequency ranges or if having problem tuning with a certain length.
Cheap because you will only need like max. 40 ft of SS-cable or isolated zinked steel wire (as often used in HAM wire antennas), cheap (HAM) isolators. Only a good isolated trhough-deck lead will cost you a bit like $30-50.

Jan
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Old 26-10-2012, 05:24   #6
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Re: Shroud as SSB Antenna?

Quote:
Originally Posted by Goudurix View Post
To me it doesn't sound as a good idea to try and use the shrouds though I have seen it installed on some boats:
- close and quite parallel to the mast all the way
- going through 3 spreaders you will need it well isolated

I would go for a far cheaper and flexible solution - indeed the "Bill B. Trayfors"-way with a sloping wire
- 1 (cheap) isolator at the top, and leading down to either side of the stern, attach it for instance the SB or port side of the pulpit with another isolator, from there some feet of GTO-15 down to a through-deck connector.
- just belowdecks have the ATU (automatic tuner); from there no problem at all to have 20 feet of good quality coax to you nav station.
- you will of course need an RF-ground system. Hundreds of liters of electronic ink have flown on that subject here....

No need for expensive backstay isolators.
Flexible because you can easily change the wire length to choose optimal frequency ranges or if having problem tuning with a certain length.
Cheap because you will only need like max. 40 ft of SS-cable or isolated zinked steel wire (as often used in HAM wire antennas), cheap (HAM) isolators. Only a good isolated trhough-deck lead will cost you a bit like $30-50.

Jan
Well, with a beam of 16 feet and shroud base near the rail, the intermediate shroud I have in mind will hardly be closer than 7 feet to the mast, until it starts to approach its upper attachment point.

And it will only go through one spreader -- I'm talking about the V1/D2 intermediate shroud.

Sounds like the setup you're talking about is the "lifeline" antenna -- haul a piece of lifeline up with a halyard; secure the bottom to the pushpit. Don't think any insulators will be needed; I would use rope at both ends.

I'm also considering that method, but trying to figure out whether using a shroud might be more permanent, adding no windage, etc.
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Old 26-10-2012, 05:44   #7
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Re: Shroud as SSB Antenna?

not to start an disagreement with the so called "experts" but i did not want to cut my backstay so we put on a gma electronics antenna -- now folks especially the experts will tell you they do not work -
however ours booms - we have had many compliments from cruisers all over the caribbean on how well our radio gets out - we have been relays for multiple cruiser nets on the hf as well as helping folks talk with chris parker -

i know a few folks will tell you that it is a waste of money but for the 5 years we have been using it - it has been great

just our opinion and what works for us
chuck patty and svsoulmates
in trinidad for hurricane season
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Old 26-10-2012, 06:15   #8
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Re: Shroud as SSB Antenna?

I've never heard of a "GMA Electronics antenna", and couldn't Google anything up, either. Can you shed some light?
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Old 26-10-2012, 06:29   #9
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Re: Shroud as SSB Antenna?

Perhaps this GAM antenna is what chuckr has in mind?
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Old 26-10-2012, 06:29   #10
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He means GAM Electronics.

Using a shroud is ok but you will need the upper insulator to be below the first spreader. If the length from there to the insulator at deck level is sufficient then it should work. 7 feet is not really optimal separation from the mast and you also have other standing rigging that is nearer I would guess. Also, the insulator at deck level may be more likely to get hit by something. Safety is a concern due to shock hazard. Only you can know what is acceptable in that regard.

Personally I would try the GAM before hacking a shroud into 3 pieces.

Dan
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Old 26-10-2012, 06:59   #11
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Re: Shroud as SSB Antenna?

Hi Dockhead,

again on the choice between an isolated shroud or a "lifeline" antenna:

- we have an example of an isolated shroudantenna in our marina but on a 2 master where it is not possible to use the lifeline or single isolated backstay approach. It looks quite neat and the antenna to tuner connection comes belowdecks quite close to the NAV station,and indeed out of the way, unfortunately the current owner does not use an SSB so I don't know how it works

- the shroud antenna will be close and parallel to the mast and other shrouds/standing rigging. Of course any type of HF antenna on a sailing boat will be close to some rigging

- knowing the enormous tension that is applied to a shroud I would not like the idea to cut it up with isolators

- the lifeline-type of antenna is easy, cheap and versatile. I have had one for many years now. I do use the (cheap) HAM type isolators on both ends, together with a strong elastic to tie the lower end to the top of the pushit, in this way I keep the wire antenna from floating too much when I tension the backstay for mainsail trim. I bring the GTO15-type wire from there down to the through-deck connector but also along stand-offs made from cheapie HAM isolators. Do not underestimate the importance of good isolators on antenna ends and bringing down the GTO15 wire to the ATU. - I have my doubts about wet rope in a salty environment.
Maybe this antenna looks less 'out of the way' and less sturdy, but it has never come down in strong winds

- if I wanted to look more "impressive" I would install a 7 m vertical pole on the stern.. the best way to have a HF antenna as far away as possible from the rigging. But that is a more vulnerable setup...
However I met a danish HAM sailor past summer coming back from the Azores. He had since long skipped his isolated backstay for a cheapie 7 m fishing rod-vertical (wire inside) with his ATU just below and he claimed a far better result (like 20dB stronger reception) ...but this is from "hearsay"...

Good luck,

Jan
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Old 26-10-2012, 09:19   #12
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Re: Shroud as SSB Antenna?

I too have had good results with the GAM antenna.
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Old 26-10-2012, 09:26   #13
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I suggest just loading up the shroud as is - as long as there isnt a path to ground near the feedpoint. See how it works on multiple bands, you may be surprised. My guess is it will work as well as a GAM antenna and nearly as well as the classic insulated backstay.

Almost any antenna on a sailboat is going to have some idiosyncrasies in radiation patterns that will vary with frequency. Experimentation is good.

Chip
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Old 26-10-2012, 09:31   #14
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Re: Shroud as SSB Antenna?

So So sorry about that - i had just gotten my first cup of coffee and listening to chris parker on sandy headed up the east coast and missed the mis spell - here it is

GAM / McKim Split Lead Antenna | GAM Electronics



good luck

just our opinion and what works for us
chuck patty and svsoulmates
in trini for hurricane season
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Old 26-10-2012, 10:32   #15
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Re: Shroud as SSB Antenna?

Quote:
Originally Posted by chuckr View Post
So So sorry about that - i had just gotten my first cup of coffee and listening to chris parker on sandy headed up the east coast and missed the mis spell - here it is

GAM / McKim Split Lead Antenna | GAM Electronics
chuckr, How high up the backstay have you mounted this?
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