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Old 23-05-2011, 22:21   #1
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Alternate 'Not-a-Backstay' Antenna

Installing an Icom M710/AT130 SSB system with a KISS counterpoise on my 2008 Hunter 38.
The boat has a B&R rig, so no backstay.
I would like to utilize coated stainless steel lifeline as an antenna as outlined many times on this and other forums by btrayfors.
I do not wish to install this in the usual backstay location or anywhere off the stern as it would cross over my solar panels.
My best alternate location is running up beside the aft port shroud (with the AT130 directly below). Antenna length would be from deck level to the second spreader. ~35'.
My question: Is the proximity to the mast and all of the associated rigging going to cause me signal interference problems?
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Old 24-05-2011, 06:30   #2
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Re: Alternate " Not a Backstay " Antenna

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Originally Posted by KnuckleDragger View Post
My best alternate location is running up beside the aft port shroud (with the AT130 directly below). Antenna length would be from deck level to the second spreader. ~35'.
My question: Is the proximity to the mast and all of the associated rigging going to cause me signal interference problems?
The rigging will interact with the antenna pattern and overall performance, just like a more conventional backstay antenna.

I think your biggest issue will be balancing distance from the shroud with interference with the main on a run. I would spend some time experimenting as modeling the system will be problematic.
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Old 24-05-2011, 08:41   #3
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Re: Alternate " Not a Backstay " Antenna

I had hoped to attach the antenna to the stay with zip ties and anchor it to the spreader at the top and the deck at the bottom. The GAM antenna is another option and it clips to the stay along the entire length of the antenna. What's the difference? They're kind of spendy though.
I should mention that the stays are grounded to the lead keel. I'm too new at all of this to know the significance of that fact.
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Old 25-05-2011, 06:39   #4
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Re: Alternate " Not a Backstay " Antenna

The GAM antenna works great on some boats and is a dismal failure on others. Boats with lightning bonded stays and shrouds definitely don't work well with the GAM but some others don't work well either. If it works it seems to work well. If I could figure out a pattern I would certainly share it.

The zip tie idea is not a good idea, particularly if your shrouds are grounded or otherwise bonded. Energy from your antenna will couple into the shroud and go to ground, which is clearly not where you want it to go.

Where are you in the world?
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Old 25-05-2011, 09:18   #5
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Re: Alternate " Not a Backstay " Antenna

KD,

I bought a GAM antenna and ended up selling it. It was too heavy and was concern about the noise since our rigs tend to act as violins. Also I did not want to drill anywhere near the chain plates for the tuner-antenna wire.

I inserted a 23ft thinned wire maybe 16 gauge inside a braided line about 45 ft long and attached to the aft end on top of the mast and to the stern pulpit (temporarily, want to add an arch but that’s a different story). I have heard that some people remove the core of the line to make it even lighter, I did not.

One of the advantages of the braided line that it stretches a little in case the mast whips around. I don’t get early enough to check-in to the nets but have been able to hear the time tones and made contact with some “hamer’s” in Alabama. The other advantage was that my tuner is closer to the antenna.
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Old 25-05-2011, 09:33   #6
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Re: Alternate " Not a Backstay " Antenna

KnuckleDragger,

I think that on your boat you really only have a few options:

1. some sort of "alternate shroud", s/s or other (like a "rope" antenna);
2. insulating a shroud and feeding that, preferably from belowdecks at the chainplate; or
3. a transom-mouted 23' whip antenna.

The first option is fraught with de-tuning problems, as Auspicious mentioned.

The second option may or may not be practical, depending on the details of your shrouds. And, if you choose to install just one insulator high up and feed the chainplate, you'll have to disconnect the grounding for that shroud.

The third option -- a SSB whip -- would work OK, if you're cool having a big vertical on the stern.

Sorry, but having no backstay and a big roach are real option-breakers in your case.

Bill
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Old 25-05-2011, 09:43   #7
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Re: Alternate " Not a Backstay " Antenna

Auspicious,
Thanks (?) for the bad news!! I could run the SS lifeline antenna freestanding from near the port chainplate hoisted to the top of the mast without intimate contact with any rigging . Mo betta?
Boat is in Portland, OR now but will live in Sea of Cortez starting this Fall.

Velero,
Have thought about a rope antenna as well. What I've read leads me to believe that a SS coated lifeline will hold up a lot longer in the marine enviroment.
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Old 25-05-2011, 10:03   #8
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Re: Alternate " Not a Backstay " Antenna

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Originally Posted by btrayfors View Post
KnuckleDragger,

I think that on your boat you really only have a few options:

1. some sort of "alternate shroud", s/s or other (like a "rope" antenna);
2. insulating a shroud and feeding that, preferably from belowdecks at the chainplate; or
3. a transom-mouted 23' whip antenna.

The first option is fraught with de-tuning problems, as Auspicious mentioned.

The second option may or may not be practical, depending on the details of your shrouds. And, if you choose to install just one insulator high up and feed the chainplate, you'll have to disconnect the grounding for that shroud.

The third option -- a SSB whip -- would work OK, if you're cool having a big vertical on the stern.

Sorry, but having no backstay and a big roach are real option-breakers in your case.

Bill
Bill,
Thanks for the reply. Been hoping you would weigh-in on this since you are "responsible" for my "alternate backstay" thinking.
Option one is really the only option with any promise. I need to make it work as best I can.
The shrouds on this B&R rig are discontinuous from deck to mast, terminating at each lower spreader tip and then jumping to the upper spreader and so on. I really see no easy, safe way to isolate an individual shroud from the rest of the rig.
A whip would be impossible with my solar panel array above the bimini and extending off the stern a couple of feet.
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Old 25-05-2011, 10:35   #9
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Re: Alternate " Not a Backstay " Antenna

why not use a shroud or other mainstay for this?? did the sea gods make a law saying we HAVE to use back stays for this use???/ i know i am able to use triatic as an antenna-- but my main back is in use as that at present.... goood luck.
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Old 25-05-2011, 11:04   #10
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Re: Alternate " Not a Backstay " Antenna

KD,

The concern I have with SS lifeline is the extra weight alof, although not structural if you get a stiff breeze it will become structural and/or vibrate putting a lot of stress on the rest of the rigging. At some point I am going to add a block at the mast head to be able to remove the antenna when not in use. The braided line that I used is like my sheets so they will last for a long time especially if I take the antenna down when not in use.
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Old 25-05-2011, 11:27   #11
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Re: Alternate " Not a Backstay " Antenna

Don't worry about the "extra weight and windage aloft" by using s/s lifeline.

First, you use the thin stuff.

Then, you pull it TIGHT. That's part of the reason for using s/s wire rope: you CAN set it up tight.

Mine has been up for some 20+ years, including 11 years in the Carribean. During that time, the boat went thru FIVE major hurricanes (with over 100 knot winds in the marina). No damage to the "alternate backstay" at all.

To me, any antenna you put on a seagoing boat should be "seagoing", i.e., able to withstand high winds and the corrosive marine environment.

Bill
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Old 25-05-2011, 11:45   #12
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Re: Alternate " Not a Backstay " Antenna

my backstay for my main is my antenna---- was rigged 6 yrs ago and not used--i had a 34 ft olympian that ha backstay rigged as antenna and 26 yrs later was still good....i dont plan on doing any quick release type of added antennae---mine has already all the antennae i should need. i wouldnt know where to place a removable stay anyway--- have enough stays shrouds and halyards hanging around.....
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Old 26-05-2011, 05:30   #13
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Re: Alternate " Not a Backstay " Antenna

I do the same as Bill, and set up the alternate backstay tight.

While not relevant to your needs, KD, the challenge comes using a permanent alternate backstay antenna on a boat with backstay adjuster. I've done installations with a dedicated cleat but that is one more thing to manage when adjusting the backstay. I'm working with a rigger to identify an appropriate high modulus connection at the top of the antenna.

For your needs, I suggest you be prepared to try a few different mounting and landing spots and do some testing. Go anchor somewhere so you won't be fighting with interference from other boats nearby and don't have to worry about multipath from other rigging.
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Old 12-11-2011, 13:54   #14
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Re: Alternate " Not a Backstay " Antenna

To update the subject.
I went with the GAM antenna mounted on the port shroud (and the KISS counterpoise) and the results are much more than satisfactory. Reception is as good or better than most other boats in the Baja Haha fleet. I have not tried to transmit, as my only real goal was to receive the weather forecasts and cruiser nets.
Installation was super simple and didn't require any services of a rigger or other professional help. Just a ride up the mast...
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Old 13-11-2011, 02:01   #15
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Re: Alternate " Not a Backstay " Antenna

Just wondering if there is any experience out there with using a MAST as a HF Vertical?

My ketch has aluminium masts so...

Interested in 80m, 40m, 20m, 17m and 15m Ham bands mostly. Maybe marine HF freqs in that vicinity. It seems an obvious possiblity, but not wanting to reinvent the wheel or have to determine it won't work independently if it's already been tried.

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