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Old 24-12-2012, 09:58   #1
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Best Antenna Location for my Ketch ?

I have a ketch rig and am preparing to install SSB.

The rig is a split backstay (red on diagram) with the lower sections about 23' long. There is also a triatic(?) stay (green on diagram) between the two masts that runs through a block at the top of the mizzen then down to a turnbuckle attached to the front of the mizzen at boom level.

I have the equipment already (ICOM M802+140AT and KISS ground).

I see at least five possibilities for the antenna element.

1/ Insulate one of the lower legs of the backstay at the triangle connector.

2/ Use both the lower legs of the backstay by insulating the upper section (forming an end fed inverted V ?).

3/ Use the triatic by insulating the connections at the top of main mast, top of mizzen and lower turnbuckle.

4/ leave the rigging alone and hoist a semi permanent "wire inside a rope" antenna or lifeline cable.

5/ Use a GAM split lead antenna clipped over one of the lower backstays.

Anybody have any advice or experience that might help me avoid wasting a lot of time and money experimenting ?

Thanks,
JM

P.S. I tried to ask this question inside another thread about Ham radio on a ketch, but the discussion seemed to be stuck on Ham equipment vs Marine SSB and Licensing.
I am licensed (VE0JM) and the equipment is already purchased so no point in discussing that here.
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Old 24-12-2012, 10:23   #2
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I would choose your ideas 1 or 2. As longer is generally better maybe use the whole backstay with an insulator 5 feet from the masthead and one on each leg 7 feet off the deck. Or whatever. Will you need to provide a conductive path between the legs and the standing upper part? I.e. is there a block there?
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Old 24-12-2012, 11:16   #3
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Re: Best Antenna Location for my Ketch ?

Thanks Daddle:

There is a Just a triangle plate with three fork terminals in the middle of the backstay:



Is there enough conduction through the pins and rigging terminals or do I need to bridge them ?

Do you have any experience with the "inverted Y" configuration you are suggesting ?

Cheers,
JM
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Old 24-12-2012, 11:31   #4
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Re: Best Antenna Location for my Ketch ?

That might conduct. But I would carry two conductors to bypass it if it gives you trouble later.

The wavelengths are so long, and the rigging bits so short, it is impossible to know what goes on with the HF radiation. All the long metal pieces of the boat affect, plus or minus, the radiation of a signal. All you can do is try. It probably makes no difference if the second, unfed, leg of the double backstay is insulated at the upper or lower end.

Might help to replace the triatic with synthetic to break up the weird loop of the two masts and triatic ... but then again, who knows? Do the simple thing and see if it works well enough.
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Old 25-12-2012, 03:20   #5
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Re: Best Antenna Location for my Ketch ?

Quote:
Originally Posted by NahanniV View Post
I have a ketch rig and am preparing to install SSB.

................
...............

P.S. I tried to ask this question inside another thread about Ham radio on a ketch, but the discussion seemed to be stuck on Ham equipment vs Marine SSB and Licensing.
I am licensed (VE0JM) and the equipment is already purchased so no point in discussing that here.
Good try
Wish you Merry X-Mas and good luck
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Old 25-12-2012, 07:50   #6
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Re: Best Antenna Location for my Ketch ?

Or you could use a 23 ft. Shakespeare whip antenna.
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Old 25-12-2012, 09:35   #7
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Re: Best Antenna Location for my Ketch ?

Our Camper & Nicholson 58 ketch is old school. I have two insulated shrouds on the port mizzen to choose from - upper and lower. Mizzen top is 48 feet.
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Old 25-12-2012, 10:00   #8
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Re: Best Antenna Location for my Ketch ?

I should have mentioned that I use a vinyl coated wire that parallels the back stay. It has a 4' rope lead at the top and a bungee at the bottom. Works fine.
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Old 25-12-2012, 21:41   #9
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There is a problem with points of marginal conduction in a transmitting antenna, and the results may not be apparent to the transmitting party.

Poor conduction between metal parts due to oxidation can create a type of non-linear diode. Putting transmit current through it can generate all sorts of high power harmonics and RFI.

I can't tell you how often this occurs, I don't know. Just a warning to be aware. A properly constructed antenna is a safer bet.

73
Chip
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Old 26-12-2012, 10:06   #10
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Re: Best Antenna Location for my Ketch ?

Quote:
Originally Posted by Celestialsailor View Post
Or you could use a 23 ft. Shakespeare whip antenna.
I did consider a whip. But, it would have to be within a few feet of my mizzen shrouds (and parallel to them) since the mizzen boom extends well past the stern (>2') and the end of the main boom is quite close to the front of the mizzen mast.
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Old 26-12-2012, 10:14   #11
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Re: Best Antenna Location for my Ketch ?

Quote:
Originally Posted by Nicholson58 View Post
Our Camper & Nicholson 58 ketch is old school. I have two insulated shrouds on the port mizzen to choose from - upper and lower. Mizzen top is 48 feet.
I had not considered using a shroud.

My mizzen is probably a lot shorter than yours. I don't think the lowers would be long enough.

Is the insulator on the upper shroud above or below the spreaders; If above, how is the spreader tip insulated ?

Thanks,
JM
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Old 26-12-2012, 10:40   #12
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Re: Best Antenna Location for my Ketch ?

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Originally Posted by SoonerSailor View Post
There is a problem with points of marginal conduction in a transmitting antenna, and the results may not be apparent to the transmitting party.

Poor conduction between metal parts due to oxidation can create a type of non-linear diode. Putting transmit current through it can generate all sorts of high power harmonics and RFI.

I can't tell you how often this occurs, I don't know. Just a warning to be aware. A properly constructed antenna is a safer bet.

73
Chip
Thanks.

I am leaning toward insulating one leg of the backstay, so not relying on the triangle plate conducting.

But, I had been thinking of feeding the antenna by connecting to the chainplate below decks, seems like a nice clean solution.

It seems like there wouldn't be a lot of corrosion between the stainless parts under tension ?

Rusty bolt effect - Wikipedia, the free encyclopedia

Do you know if there is a simple way I can test for this condition ?

73s
JM
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Old 26-12-2012, 10:45   #13
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Re: Best Antenna Location for my Ketch ?

Simpler to put a tiny jumper around the fittings and then not worry about it. You can feed it from below decks if it is well insulated from the hull and other rigging. Try not to touch it while transmitting.
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Old 26-12-2012, 11:00   #14
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Re: Best Antenna Location for my Ketch ?

my vhf antenna is on masthead. my ssb antenna is my main mast port side backstay. my garmin antenna is built into machine/.
yes my formosa is ketch rigged.
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Old 26-12-2012, 11:59   #15
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Re: Best Antenna Location for my Ketch ?

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Originally Posted by NahanniV View Post
Rusty bolt effect - Wikipedia, the free encyclopedia

Do you know if there is a simple way I can test for this condition ?

73s
JM
You are probably right that stainless parts under fairly high tension would be unlikely to manifest this problem. Thats just a gut feeling of mine too, but I find there are frequently exceptions to my gut feelings! I think daddle's advice is good - put a jumper around potential problem points for good measure. I don't really know if there is a simple way to test for "rusty bolt effect". You could start by measuring the resistance across a questionable connection. That might not rule out the possibility, but if the ohmeter reads more than a few tenths of an ohm I think the connection would be suspect.

Chip
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