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Old 18-10-2009, 18:33   #1
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Length of Insulated Backstay for Ham Radio

Length of Insulated Back stay for Ham radio
This winter I am changing my 2 back stays for a single 3/8 Back stay with insulators to allow use of Ham radio. Any advice out there as to what length of wire between both Insulators I should use?
I do not have SSB radio yet but will purchase before going off shore. I am changing the standing rigging this winter and while I am at it I plan to set up back stay for antenna.
Is there a set length for each radio antenna what is it. Or does the length depend on the radio etc
Any advice appreciated
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Old 18-10-2009, 19:59   #2
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I think the minimal length is about 22 feet with an antenna tuner. Without the tuner the antenna would only be optimized for a narrow frequency band.
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Old 18-10-2009, 20:32   #3
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Minimum length of 23', measured from the antenna tuner. About 40' is a good length.

Three ways to go:

1. Traditional insulated backstay, with insulator a few feet from the top and an insulator near the bottom -- often 8' or so above the deck. Antenna fed with GTO-15 wire from antenna tuner belowdecks, close to base of backstay.

2. Just install a single insulator near the top of the backstay. Feed the backstay/antenna from the chainplate belowdecks. No thru-deck needed. Works well unless you have a hydraulic backstay adjuster. Cheaper, fewer potential points of failure, more efficient due to very short run of GTO-15 from tuner to chainplate. You can put nylon or pvc boot on lower part of backstay if you're worried about someone grabbing it while you're actually transmitting.

3. Forget the backstay altogether. Rig an "alternative backstay", made from s/s lifeline. Pull one end up with a spare halyard (or dedicated halyard). Tie lower end off to pushpit on one side. Feed at lower end with GTO-15 thru-deck to tuner just underneath. No need for expensive insulators. No potential points of failure on your standing backstay. Works every bit as well as a traditional backstay. Very robust (mine is almost 20-years old). See pic at: DSC_0028

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Old 19-10-2009, 14:36   #4
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Is there a reason why everyone seems to use the back stay? why not one of the shrouds? afterall most have the chain plates going through the deck which would keep the connection clean and away from water?

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Old 19-10-2009, 14:39   #5
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Keep the lower insulator above anyone's reach. Toching when transmitting at full power could be painful or worse.
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Old 19-10-2009, 14:59   #6
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Pete,

The reason for use of the backstay is to keep the antenna as far away from other rigging as possible...in the clear, so to speak. Shrouds work OK, but on most boats not likely as well as the backstay due to proximity to the mast and other shrouds.

There are exceptions, though. I'm finishing the install on a big cat which has no backstay and only ONE shroud on each side. Insulating one of them at the top, and feeding the chainplate at the bottom.

The danger of RF burns "and worse" is highly overblown, IMHO. I've never seen one in over 40 years of hamming. Hey, you could certainly feel a tingle, and most people would be smart enough to remove their hand quickly. Also, you can insulate the lower portion of the shroud or backstay or whatever with a PVC or nylon boot if you're really worried about it.

Understand, we're talking here about small cruising sailboats, not about commercial passenger-carrying vessels. Easy enough to warn the crew to not grab the XXXX while you're actually transmitting, which is the only time there's the possibility of an RF "burn".

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Old 19-10-2009, 16:02   #7
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Thanks everyone for you help.
From what I gather anything from 23 to 40 feet would work with a tuner.
Secondly I hear one may get away with one insulator placed about 1 foot from the top of mast.
I expect my rig will end up having a Y about 8 feet up (2)’ SS wires tied to one 3/8 “ SS back stay
Bill you indicated min 23 feet from Tuner did you mean from where the tuner wire connects to the back stay as the distance from tuner could vary quiet a bit inside then through hull up the ” leg to 3/8” backstay etc.
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Old 19-10-2009, 16:37   #8
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Sergy,

In your original post, you said you were replacing those 1/4" stays with a single 3/8" backstay. I had understood, therefore, that you would have just that, i.e., a single 3/8" backstay (on the centerline of the boat).

Now, it appears you're still talking about a split backstay, only in a Y configuration, with two 1/4" lowers and a single 3/8" upper. Is this correct?

Too bad, if this is the case. It would have been easier with a split backstay consisting of two 1/4" wires all the way from the deck to the truck of the mast.

The Y configuration can complicate things a bit. Matter of fact, I'm going to troubleshoot one such installation tomorrow.

If, indeed, that's what you're going to do, then it would probably be best to install an insulator near the top of ONE of the two 1/4" stays, just below the Y in order to insulate this lower backstay from the rest of the antenna. Then, install an insulator near the top of the 3/8" stay a few feet down from the truck of the mast. Feed the other 1/4" stay from belowdecks. I'm assuming that the Y connection is electrical as well as mechanical, between the 1/4" and the 3/8" wires.

And, yes, I meant from the TUNER itself. The GTO-15 wire is a radiating part of the antenna. You want to locate the tuner as close as you can to the base of whatever you choose for an antenna.

Just out of curiosity, why are you replacing the two 1/4" backstays with a Y-configuration?

Bill
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Old 19-10-2009, 16:58   #9
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Thanks Bill
It would be much easier if I stayed with the (2) back stays from chain plate to top of mast.
The only reason I am considering doing the split to 3/8 is I was told by Rigger that 2 backstays was not as good as (1) 3/8 ??? I choose to split because I have 2 chain plates at the back of the boat one on each side. The more I consider this I am leaning to stay with the original configuration. Therefore
It seems that it would make adapting one back stay for antenna much easier. Any thoughts The original owner had run a seperate wire with insulators along the side of back stay and it keept swinning in the wind so I removed and hope to make it neater by using the backstay.
The 2 back stays have been up for 25 years so something is right.
Ps there is a whole bunch of looks like 2 " copper webbing criscrossing through the builge area I presume this is the Ground plane that I will need.
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Old 19-10-2009, 18:14   #10
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I'd suggest getting advice from a HAM! The length of the antenna makes up half of the sine wave required for transmitting, and the grounded tuner creates a full sine wave length based on the frequency that you're transmiting. Different wave lenghts for different frequencys.
DON'T TOUCH THE ANTENNA WITH THE TRANSMIT KEY DEPRESSED. iT CAN KILL YOU. This is why the backstay is used, The longer length allows the bottom insulater to be out of reach.
If you doubt this, hold a fluorestent tube lengthwise about two inches from the antenna and press the transmit key. It turns on!
Install the tuner at least three feet from your inverter as the RF from the tuner can fry the inverter. Also install the tuner as far away from the radio as possible(at least three feet).
Regards John A - KC6LRY
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Old 19-10-2009, 18:50   #11
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JohnA -

btrayfors is a ham, and your antenna wave theory is a bit off. Also, a transmitting antenna, at the 100 - 150 watts max output of typical marine transceivers, can cause surface burns but won't kill you. Much, much higher outputs might cook you, but the frequency is too high to depolarize heart and skeletal muscle. RF energy like this, at much lower frequencies, is actually used in the operating room to cauterize bleeding points, and people do not die from it.

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Old 19-10-2009, 19:05   #12
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John A.

I've been a ham for for some 50 years, during which I've built ham transmitters, receivers, even a few televisions and stereo systems from kits. I've installed hf gear on boats, cars and airplanes. So, I have some first hand experience about the subject.

No one is likely to be killed from touching an antenna when it is energized by a radio frenquency (RF) signal from ham/marine hf gear on a recreational cruising boat; I believe that other experienced folks on this forum would agree that we don't want to spread false information that would unnecessarily frighten people.

Perhaps a tight grip might actually result in a small burn (I've received a few), but anyone that is gripping an antenna is sure to release it very quickly. I'll give you the remote possibility that someone could be startled and perhaps fall overboard and drown, but the RF signal isn't going to kill anyone.

Energizing a light bulb with RF energy is quite different than energizing it with alternating current (AC), which can be lethal, but has no connection within the context of RF in this discussion.

Roger
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Old 19-10-2009, 19:24   #13
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I've no probem with your post, but maybe you can tell me why people are killed while one person is on a roof turning an antenna for maxmium reception while a second person is keying the mike and transmitting? I've lost two friends that way.
It's entirely possible that they suffered heart attacks and died in the fall, so yeh, touching the antenna was not at fault.
I was only quoting Gorden West, a person on the west coast who has given semminars for twenty years on Ham Radios. I received my first license from him during a semminar on marine ham radios many years ago, and the information may have been deluded as age progresses.
So heck, I can be wrong.
Have a good day.
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Old 19-10-2009, 19:34   #14
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Sergy:

You asked about the "ground". Don't think of the ground for the tuner and/or radio as an electrical ground for electrical safety. The ham radio ground is the counterpoise against which the energy is dispelled from the antenna. You don't need contact with your keel, a large mass of metal, or a great conductor to the water. The important factor is a large metal surface area against which the signal can push towards the antenna. I have used metal tanks and even the total amount of lifeline as the ground satisfactorily. Now, especially since being told that getting my water and fuel tanks involved in the energy use is just not smart, I have simply bought 25 feet of that tinned woven copper belt that is sold at auto maintenance stores for the purposes of grounding. I connected it to the appropriate wire on the tuner and unwove it just under the floor boards, and kept it separate and insulated from all other electrical grounding - which normally includes the engines, spars, other electrical components and the negative terminal of your batteries. The thin strands of wire in the belt have tremendous surface area, and the tinning appears to slow down the corrosion. I have been told I have the best 20 metre signal in the Caribbean.

The counterpoise has nothing to do with the other electrical grounding, and has no need to be connected to it. I don't know if using the electrical grounding might be a problem, causing sparks, corrosion, or the like; but why mess with it if it isn't necessary?

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Old 19-10-2009, 20:23   #15
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Originally Posted by Sergy View Post
Thanks Bill
It would be much easier if I stayed with the (2) back stays from chain plate to top of mast.
The only reason I am considering doing the split to 3/8 is I was told by Rigger that 2 backstays was not as good as (1) 3/8 ??? I choose to split because I have 2 chain plates at the back of the boat one on each side. The more I consider this I am leaning to stay with the original configuration. Therefore
It seems that it would make adapting one back stay for antenna much easier. Any thoughts The original owner had run a seperate wire with insulators along the side of back stay and it keept swinning in the wind so I removed and hope to make it neater by using the backstay.
The 2 back stays have been up for 25 years so something is right.
Ps there is a whole bunch of looks like 2 " copper webbing criscrossing through the builge area I presume this is the Ground plane that I will need.
Sergy,

Yes, the original configuration would certainly be easier.

I'm no rigger so can't comment on the advice you were given, but if you're still in doubt why not consult another professional rigger? And, as you say, the present setup has worked fine for 25 years!

What to do? Just install a single insulator in one of the 1/4" backstays, up near the top. Maybe 2-3' from the top. Then, feed that backstay from belowdecks, attaching a short length of GTO-15 wire to the chainplate.

Attach your RF ground to the tuner's ground lug. If you don't have one, or the one that's there is somehow compromised, just run a length of copper from the tuner ground lug to the nearest bronze thru-hull. Attach it securely, and you're good to go.

If you later find it difficult to tune on one band or another, you can add radials (tuned or untuned), or further attach your RF ground to convenient metal fittings (like pushpit/pulpit/lifelines, toerails, s/s rubrails, rudder complexes, etc.).

Have fun, and let us know how it works out.

Bill
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