SSB Radio: Backstay Insulators - what's the deal?

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demonboy

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SSB Radio: Backstay Insulators - what\'s the deal?

I'm hoping to install an Icom M710 on our boat and am aiming for the cheapest option, which I believe is to use the backstay as the whip and get the boatyard to fit insulators on the backstay.

I've read a little on this and most people seem to be replacing their backstay at huge cost! What's the deal? I thought I just bought some insulators that the boatyard wrap round the backstay. Am I missing something here or got the wrong end of the stick?
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

Hi Michael,

I thought the insulator was a plastic thing that prevents electric shocks or something and covers most of the backstay. Obviously I'm wrong as a quick search for Stalock shows a small connection for each end of the backstay.

I'm interested: what does the insulator do and did the purchase of these two insulators completely negate the need to buy a £300 whip aerial?
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

Insulators insulate a section of the rigging from the rest of the rig, turning it into an aerial of defined length. This involves cutting the backstay at the top and bottom to attach/insert the insulators. As this requires more wire than exists it is normally necessary to replace the backstay.

The backstay is used as it is the longest single length of 'wire' on the boat.
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

Interesting. I have a ketch, so the backstay will be shorter than a normal backstay on a sloop. Reckon that will make a difference?

Thanks for your replies so far.
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

[ QUOTE ]
Insulators insulate a section of the rigging from the rest of the rig, turning it into an aerial of defined length. This involves cutting the backstay at the top and bottom to attach/insert the insulators. As this requires more wire than exists it is normally necessary to replace the backstay.

The backstay is used as it is the longest single length of 'wire' on the boat.

[/ QUOTE ]

The wire between the insulators needs to be a minimum of 7 meters.
The first insulator needs to be above head hight. you dont want anyone leaning on it or touching it while transmitting
rob
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

[ QUOTE ]
As this requires more wire than exists it is normally necessary to replace the backstay.[ QUOTE ]


No, this is not the case. When you insert the insulators you increase the length of the backstay, so you must reduce the remaining wire to compensate and can therefore use the existing backstay. I've done several of these for other boats as well as my own and never yet had to replace a backstay.

Incidentally, I suggest that the wire length between insulators and forming the antenna is around 11 metres.
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

[ QUOTE ]
The first insulator needs to be above head hight. you dont want anyone leaning on it or touching it while transmitting [ QUOTE ]


Whilst apparently sensible, I usually advise people to have the bottom insulator a little lower than this so that the feeder connection is readily accessible for maintenance, which will certainly be necessary on a regular basis to maintain a high quality connection.

One often hears this warning about not touching the antenna whilst transmitting and I understand that nasty burns can result, but has anyone actually seen or know someone this has happened to? It beggars belief that anyone would be stupid enough to be hanging onto a backstay while that was being done!!
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

[ QUOTE ]
The wire between the insulators needs to be a minimum of 7 meters.
The first insulator needs to be above head hight. you dont want anyone leaning on it or touching it while transmitting rob

[/ QUOTE ]

No idea where you get the 7 metres from? Most Marine auto ATU's will sort out the random impedence presented by the backstay at whatever maritime frequency you decide to communicate on.

Also although it might make sense to have the insulator above head height to avoid RF burns, it doesn't take much to ensure that no-one is hanging off the backstay if you are about to use the SSB. Many the time I've yelled from the saloon, "Please keep clear of the backstay - I'm about to use the SSB..."!

And to the person who wondered whether it really is possible to get RF burns, yes it is. I used to work in high power RF and it hurts... Some say its worse than DC which is generally reckoned to be a 'bad shock'.

Finally, you can use the original backstay as you end up removing wire to fit the insulators. The insulators aren't 'wrapped round the wire' by the way, but they form part of the rigging. Last time I looked a pair of Sta-lock insulatoirs for my backstay were £300 - so not sure if I will save very much over a £300 whip..
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

From my experience An RF burn is not a shock, you don't feel any tingling. What you get is intense localised heating froma an arc which stings and burns. For lower power if you grasp the wire firmly there is no arcing or burning it is the very light touch that really gets your attention.

Yes I would put the bottom insulator closer to the deck for maintenance. If you are concerned about people being burned then insulation around the lower part of the backstay will avert problems.

Insulators used in a backstay are usually the roll swaged type where the wire goes into a socket which is squashed. The insulation material taking the load in tension. A piece of backstay is cut out.
Radio aerial masts used to use egg insulators of porcelain. The wire was passed through holes such that one loop of wire looped through the other loop and the porcelaine was in compression. This style have been used for boat stay aerials however obviously the loops consume a lot of extra backstay wire.

The backstay is used mainly because it is the most remote wire from the mast and any paralell wire which will suck the power away. In the same way a wire hauled up to the mast is not as efficient. Or in the same way on radio masts they break up all the stays with insulators.
In the case of a ketch if you want a longer aerial the triatic stay could be insulated and connected via a down wire to the tuner (which will be part of the aerial) or via a connection to the insullated backstay. good luck olewill
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

[ QUOTE ]
[ QUOTE ]
The wire between the insulators needs to be a minimum of 7 meters.
The first insulator needs to be above head hight. you dont want anyone leaning on it or touching it while transmitting rob

[/ QUOTE ]

No idea where you get the 7 metres from? Most Marine auto ATU's will sort out the random impedence presented by the backstay at whatever maritime frequency you decide to communicate on.


[/ QUOTE ]

The icom website says
Required Antenna element length to achieve full proformance varies according to the lowest frequency 1.8mhz band 7 meters or longer 4mhz band 3meters or longer. The longer the antenna element the better the antenna efficency.

not my words icoms

Rob
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

Yes

I have been stupid enough to be on the receiving end of an RF Burn.

Its not like touching a hot object

It burns from the inside outwards.

By the time you feel it there has been a lot of damage, a very deep burn.

I would suggest having the botton insulator low enough to be able to easily remake the connection but I would put some plastic tubing round the bottom few feet of aerial.

At one time I used a powerful RF amplifier to an aerial which trminated in a tree. It killed the tree!

High power RF is not something to take lightly.
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

[ QUOTE ]
The wire between the insulators needs to be a minimum of 7 meters.
The first insulator needs to be above head hight. you dont want anyone leaning on it or touching it while transmitting rob

[/ QUOTE ]

No idea where you get the 7 metres from? Most Marine auto ATU's will sort out the random impedence presented by the backstay at whatever maritime frequency you decide to communicate on.

The icom website says
Required Antenna element length to achieve full proformance varies according to the lowest frequency 1.8mhz band 7 meters or longer 4mhz band 3meters or longer. The longer the antenna element the better the antenna efficency.

not my words icoms

Rob

[/ QUOTE ]Who am I to argue with ICOM. Actually - what they say doesn't contradict what I said. After all they say you can use 4 metres of backstay for 7Mhz and higher - but who has a backstay 4 metres long? Also their comment is a bit of a generalisation. A more effective vertical is one that is close to a quarter wave of the frequency used. Other lengths present an odd impedence which the ATU transforms to allow the transmitter to think its 'looking at' 50 ohms impedence. If the wire is too short, not only does the wire become very inefficient at low frequencies, but you get higher losses in the ATU. But here we are getting into radiation resistance, and not impedence mismatch...

The length of 7 metres that they suggest is not some invisible electronic wall, but their suggestion as to what might be OK with their ATU.
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

[ QUOTE ]
From my experience An RF burn is not a shock, you don't feel any tingling. What you get is intense localised heating froma an arc which stings and burns. For lower power if you grasp the wire firmly there is no arcing or burning it is the very light touch that really gets your attention.


[/ QUOTE ] We will have to disagree Will. I don't fancy touching the antenna (or getting anwhere near it) at high power. RF burns at high power are nasty things and at microwave frequencies they are extremely dangerous.
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

Agree with Morris - the bit of stay that has to be the aeriel must be insulated from the rest of the rig. All the setups I've used had the bottom insulator right above the lower rigging screw, with the feed to the set clamped to the wire just above the insulator.

Exact length/position of the aeriel is fairly unimportant, although long is better than short. As Morris says the ATU will compensate for whatever length you end up with. In my experience the sets with the best ground get the best transmission/reception. Either ground to a metal keel or to a really big conductive foil inside a GRP hull.
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

I think all the others have answered you but:

The two insulators in the back stay can be any distance apart but the further the better. The lower insulator should be out of reach - well too high for people to put there hands out and touch the wire above it easily - so they do not get burned.

Remember when you put the two stalock insulators in you effectively make the back stay a bit longer - so measure the extra length and cut the extra length out at one of the joins.

You do not need a whip antenna when using the back-stay - it works very well indeed...
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

Thank you all. You've answered my initial questions and given me additional food for thought.

I'm still a little confused when people say "put the insulator as low as possible" though. Surely the insulator is replacing the swage fitting at the bottom (and top) of the backstay, so by default the insulator is attached to the chain plate at the deck? Is this not the case? Michael's post suggests that the lower one should still be above head height.......
 
Re: SSB Radio: Backstay Insulators - what\'s the deal?

[ QUOTE ]
Thank you all. You've answered my initial questions and given me additional food for thought.

I'm still a little confused when people say "put the insulator as low as possible" though. Surely the insulator is replacing the swage fitting at the bottom (and top) of the backstay, so by default the insulator is attached to the chain plate at the deck? Is this not the case? Michael's post suggests that the lower one should still be above head height.......

[/ QUOTE ]

Where the insulator is will only make a difference as to whether you can touch the bare antenaa or not. In fact the wire you run up to the backstay from the ATU will also form part of the 'antenna'.

If you look at the insulators available, you will see that they don't usually replace the end terminal, but are put into the backstay. That's why you get a choice where to break the wire and insert the insulator. They look something like this:
catpic_043_rgb_200by200.jpg
 
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