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Old 22-04-2018, 00:12   #1
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HF Antenna off set by a cable tie and hose

Hi All My boat is up for new rigging and I am not in favour of insulated backstays after seeing 2 collapse in Disaster.
I have seen a couple of rigs with the HF cable run alongside of the Backstay set off by 100mm with plastic conduit and a cable tie for about 45 feet.
I am concerned for transmitting getting away so I am asking for advice before I start work on the mast.
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Old 22-04-2018, 08:24   #2
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Re: HF Antenna off set by a cable tie and hose

I don't have a lot of experience with this but my understanding is if done properly you can actually get better radio signals with the antenna next to the backstay as opposed to actually being the backstay.

GAM makes an antenna that goes over the backstay.

There is also the Rope Antenna. I've seen two of these recently but cannot comment on their performance.
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Old 22-04-2018, 08:39   #3
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Re: HF Antenna off set by a cable tie and hose

Yes, the GAM antenna is a commercial version of this, where the antenna wire is clipped adjacent to the backstay. It apparently works pretty well, but I know of one boat that tried it and had tuning problems on some bands. Those guys ultimately used a "ropeantenna" style antenna that gave them more separation from the backstay, and this worked better for them. I don't recall if they built or bought that wire-inside-rope antenna.

In theory, you want to have good separation between the antenna and rigging. However, your tuner can usually compensate for the parasitic coupling, to a point anyway. Even if properly matched by the tuner, you may get more loss than with a proper insulated backstay or well-isolated vertical. But "a little more loss" is usually not a big problem, and compromises are pretty common in our boat radio systems.
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Old 22-04-2018, 12:05   #4
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Re: HF Antenna off set by a cable tie and hose

Personally I'd revisit the insulated back stay and use stay lock terminals rather than standard swage terminals. I've never heard of a staylock or norseman failure although I'm sure it may have happened but it would be rare if properly installed plus if your a long term cruiser you can simply buy new cones and reuse the your staylocks when you rerig.If you really don't trust any terminal you should forget sailing as that's what's holding your whole rig up plus if anything is going to fail it will be your forestay not your backstay.
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Old 23-04-2018, 06:14   #5
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Re: HF Antenna off set by a cable tie and hose

The backstay insulators that I have heard of failing have always been undersized. The insulators are pretty expensive, and some people try to get by with the smallest (read cheapest) one that they can. The results are predictable.

I have, personally, never heard of a properly sized backstay insulator failing.
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Old 23-04-2018, 06:35   #6
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Re: HF Antenna off set by a cable tie and hose

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Originally Posted by rosco4271 View Post
.....
seeing 2 collapse in Disaster.
....
Do you remember any of the details about these rigs ?

I don't know about antennas parallel to rigging, but a rope antenna is easy to make and can work well. On my previous boat I made one entirely out of GTO15 wire that ran continuously from the tuner, thru a deck gland, and was hoisted up in the rigging.
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Old 23-04-2018, 10:48   #7
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Re: HF Antenna off set by a cable tie and hose

The closer to parallel, and the closer to other metal, that your antenna is, the more signal loss you will have.

That's why, in cases where the feed is mounted to a backstay (or other aloft-leading wire), you'll see standoffs.

How much signal you're willing to sacrifice will drive your decision. We use a whip antenna, which is vertical (which is the best propagation mode, as the pattern, seen from above, would be round, rather than oval as it would be for an angled antenna).

We routinely (whenever we're on, of course) act as relay for other boats, and my signal is usually very good wherever we're heard (such as, e.g., in CA or WA, from the Bahamas or US SE coast). That despite having "only" a 23' whip vs a (typical) 60 or greater foot longer backstay.

FWIW, the founder of the SSCA ham net has a trawler, with dual whips aside his topsides house; he gets even better than I. He posits (doesn't know for sure, but he certainly has the chops for HAM) that they are reinforcing at that distance.

YMMV, but if you ARE going to do it as you suggest, I suggest that you use the longest standoff you can rely on. OTOH, your antenna, at right angles to other metals, has little to no loss.

Ref:

http://www.marines.mil/Portals/59/Pu...-15-092827-423

EMI ? Electronagnetic Interference in industrial instalation and much more... | SMAR - Industrial Automation
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Old 23-04-2018, 11:25   #8
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Re: HF Antenna off set by a cable tie and hose

All sailboat antennas are a compromise. None of them are resonant and the grounding systems (counterpoise) poorly match.

You are starting out with limitations - don't make it worse. An insulated backstay is a better option than a whip. A wire parallel to the backstay will have a very attenuated and directionalized signal.

I have had backstay insulators on my boat for it's 32 year life with no issues. If you truly dislike that option consider some of the new synthetic standing rigging and then run your wire next to that.
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Old 23-04-2018, 12:41   #9
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Re: HF Antenna off set by a cable tie and hose

Install a Dyneema backstay.

And fid into the Dyneema rope a 14AWG copper wire for as long as you need.
Clean, neat and simple.

Check Colligo Marine rigging. They do this all the time.
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Old 23-04-2018, 12:54   #10
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Re: HF Antenna off set by a cable tie and hose

I use an insulated piece of lifeline, hauled up on the spare main halyard. It basically stays up there all the time

Installing an ICOM802 SSB Part 1: Creating and installing an alternative backstay antenna - Life on Gudgeon
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Old 23-04-2018, 13:52   #11
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Re: HF Antenna off set by a cable tie and hose

We have something very similar. We have the GTO wire from the tuner coming out on deck and connected to a copper braided wire which is hauled up to the spreader with a bungee at one end to keep it taught.

We have been told we have very good reception, so our combination of antenna, tuner and ground (plate in water and copper lined locker) seems to work

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I use an insulated piece of lifeline, hauled up on the spare main halyard. It basically stays up there all the time

Installing an ICOM802 SSB Part 1: Creating and installing an alternative backstay antenna - Life on Gudgeon
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Old 23-04-2018, 14:03   #12
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Re: HF Antenna off set by a cable tie and hose

Our antenna is stood off from our mizzen rigging exactly as you describe, but it then runs inside a piece of rope to the top of the main mast an an angle different than the backstay.

While we are still getting used to the SSB, previous owners circumnavigated with and used sailmail frequently, so I presume it worked well enough for that.
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Old 23-04-2018, 23:31   #13
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Re: HF Antenna off set by a cable tie and hose

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A wire parallel to the backstay will have a very attenuated and directionalized signal.
This isn't necessarily so. Attenuation will depends a lot on the tuner, and there will be little effect on directionality when the backstay / antenna separation is under a few feet (which is virtually always the case).

Still, it's better to try a different approach.
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Old 24-04-2018, 00:37   #14
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Re: HF Antenna off set by a cable tie and hose

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This isn't necessarily so. Attenuation will depends a lot on the tuner, and there will be little effect on directionality when the backstay / antenna separation is under a few feet (which is virtually always the case).

Still, it's better to try a different approach.
An antenna tuner is not a magic box that corrects antenna deficiencies. All an antenna tuners does is transform impedance so that a transmitter can push more power into the antenna.

What that antenna does with that increased power is another issue. Having that antenna (radiator) adjacent to another conductor (a random inductor) will change the radiation pattern. It's affect will vary with frequency. Furthermore, if that parallel wire is part of grounded standing rigging electromagnetic energy will be bled off to ground.

An ideal antenna radiates electromagnetic energy in the direction and takeoff angle that is best for communications. An random length end fed sloper is not that good to begin with. Handycapping it with a parallel untuned element can't be helpful. Think of this as a balanced feedline (ie ladder line) with no antenna at the end.
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Old 24-04-2018, 01:16   #15
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Re: HF Antenna off set by a cable tie and hose

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Originally Posted by stormalong View Post
An antenna tuner is not a magic box that corrects antenna deficiencies. All an antenna tuners does is transform impedance so that a transmitter can push more power into the antenna.

What that antenna does with that increased power is another issue. Having that antenna (radiator) adjacent to another conductor (a random inductor) will change the radiation pattern. It's affect will vary with frequency. Furthermore, if that parallel wire is part of grounded standing rigging electromagnetic energy will be bled off to ground.

An ideal antenna radiates electromagnetic energy in the direction and takeoff angle that is best for communications. An random length end fed sloper is not that good to begin with. Handycapping it with a parallel untuned element can't be helpful. Think of this as a balanced feedline (ie ladder line) with no antenna at the end.
I do understand this, and agree with much of it. But the balanced feedline comparison is quite problematic, and the coupled backstay is much more than an inductor. Any change in directionality will be more of a takeoff angle / lobe issue caused by an effective lengthening of the antenna due to the coupled backstay. And a coupled grounded radiator element can be quite efficient (see the J-pole or gamma-match for grounded element examples).

Anyway, I assume that we can agree that any effects will be frequency-dependent and somewhat random -- much like the behavior of a backstay antenna itself.

And yes, antenna tuners (matching networks) can be quite lossy when working into extreme impedance differences.

All this is why the "GAM" antenna (antenna wire clipped closely to the backstay) works well in some cases, and not so well in others.
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