Insulated backstay question for SSB experts

jerrytug

jerrytug

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Hello if anyone could answer this slightly obscure question I would be grateful.

I'm hopefully buying a yacht with twin backstays, fitted with a SSB radio, aerial tuner etc.

The backstays are widely separated where they attach to the stern, but join the same fitting at the aft side of the masthead.

Both the backstays are insulated at top and bottom.

One of them is connected to the tuner in the lazarette in the usual way.

The other insulated backstay is not connected to anything.

I have just got a quote for renewing the 22-yr old rigging ( from a reputable rigging company) and he says there is no point in having both backstays insulated, just the one connected to the tuner.

However, I thought both might have been insulated for a reason, that being, interference/interaction between the two.

I will bounce this query off my ham club, but no meetings til next year.

Is there a good reason to insulate BOTH backstays? Cheers Jerry
 
I would suspect the other backstay might form a coupled loop, backstay-guard wires-forestay?
It gets complicated, and it's not exactly my field, but I think life is simpler if these things are either properly insulated or properly short circuited.
There always seems to be a bit of trial and error involved in HF set ups, so if you have something that's well sorted, try not to change it?
The other backstay will be fairly coupled to the aerial one near the top, it will make a difference if the mast is connected or insulated.
Very hard to estimate how big a difference though.
 
No, it is not necessary to have both insulated and your rigger is quite correct.

The backstay serving as an aerial should be insulated at the bottom and part way up the backstay (depending on its length). The tuner should be connected to the backstay as close to the bottom insulator using the shortest length of cable possible between the tuner and the backstay taking great care that the cable is properly tied to the backstay. I have exactly that arrangement and it works perfectly - albiet my insulator is about 2/3rd the way up.

It is usual to cover the part of the back stay within reach with a plastic sheave to avoid any accidents as the wire can get really hot when used on full power.

If you think about it assuming the Genoa is mast head then the same would apply to the foresay as this will also join the mast almost as close as the other backstay.
 
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ip485 said:
No, it is not necessary to have both insulated and your rigger is quite correct.

The backstay serving as an aerial should be insulated at the bottom and part way up the backstay (depending on its length). The tuner should be connected to the backstay as close to the bottom insulator using the shortest length of cable possible between the tuner and the backstay taking great care that the cable is properly tied to the backstay. I have exactly that arrangement and it works perfectly - albiet my insulator is about 2/3rd the way up.

It is usual to cover the part of the back stay within reach with a plastic sheave to avoid any accidents as the wire can get really hot when used on full power.

If you think about it assuming the Genoa is mast head then the same would apply to the foresay as this will also join the mast almost as close as the other backstay.
Click to expand...

Thanks ip. Good point about the forestay, it never occurred to me.. cheers Jerry
 
ip485 said:
... It is usual to cover the part of the back stay within reach with a plastic sheave to avoid any accidents as the wire can get really hot when used on full power.
Click to expand...

1) That sounds like a rust inducer as discussed under headings of shroud and lifeline covers.

2) If the wire is getting hot that sounds like wasted power (and possibly poor matching). Would it not be better to (loosely) wind a copper wire around the insulated portion of the backstay and clamp it to the stainless at top and bottom? Most of the current would then flow through the copper since the stainless will have a much higher resistance.

Mike.
 
I've got a similar arrangement, and have only got one backstay insulated... in my case, the top insulator is as high as I can safely get it, and the lower one, just high enough that any stay that might be reasonably grabbed as a handhold while making aft is below the bottom insulator... still leaves a good length of stay for the aerial... I haven't mounted the tuner yet (another job on the long list!), but will also put a plastic cover over the lower length, if nothing else, to avoid any conducted heat causing problems.
 
>If the wire is getting hot that sounds like wasted power (and possibly poor matching).

When transmitting HF if you hold the wire above the insulator you will cook your hand from inside out like a microwave. To stop any visitor doing that I used to light a cigarette on the wire. Below the insulator is fine because the ATU wire is obviously connected above the insulator.

You don't need two insulated back stays but I wouldn't bother to spend the money on a new stay the insulators are doing no harm and don't affect the strength of the backstay.
 
KellysEye said:
When transmitting HF if you hold the wire above the insulator you will cook your hand from inside out like a microwave. To stop any visitor doing that I used to light a cigarette on the wire. Below the insulator is fine because the ATU wire is obviously connected above the insulator.
Click to expand...

So does the wire get hot or not? (I know nothing about lighting cigarettes!)

Mike.
 
Thinking back to my days operating high power HF sets in the Army, the worry we used to have wasn't the actual temperature of the connections to the antenna but the way the HF signal would induce localised heating in any flesh in contact with it when transmitting. Holding your hand near to any part of the antenna system would mean it felt warm: actually holding it could quite literally cook your hand. As a demonstration of the dangers inherent in HF radios, we used to do a demo: inside the hanger, we'd set up a station and then transmit on high power. All the flourescent tubes in the hanger would light up from the HF energy. Mind you, that was with the Larkspur system, which kicked out about 2.5kw via a rotary amplifier......
 
ip485 said:
taking great care that the cable is properly tied to the backstay.
Click to expand...

If you mean 'taking care that the cable is properly connected to the insulated part of the backstay' that is correct.

But don't be tempted to tape the rising lead from the tuner to the uninsulated part of the backstay. I've seen many set-ups like that. All you get is the poor ATU trying to match the tx to the entire boat.
 
Hot not in the sense of direct heat but rf energy. The plastic sheeve should be thin pipe its not like the material used on guard rails. Any water readily drains as it should be a loose fit. There is no cause for concern about corrosion. The sheeve serves as not much more than a warning not to hold the backstay and mine has some hazard type tape wrapped around it to serve the purpose. Icom specifically state the wire from the tuner should be as short as possible (no more than a meter i recall) hence the insulator should be as close to the base of the stay as possible and why there is no uninsulated stay below as old varnish says. My icom puts out 150 watts, thats a reasonable amount of energy and you really dont want to be grasping the backstay while i am transmitting.
 
Btw my broadband dome and digital tv dome sit only a foot or so in front of the backstay so i was cocerned to see if the ssb would interfere although i appreciate very different frequencies. So far there appears to be no interference between any of the systems. Even the coax to the tracvision, the inmarsat and the ssb route along the same conduit but without issue!
 
Before I disconnected my SSB (!) the insulated cable was held off the backstay by a set of fat cable ties. In essence a big loop including cable and backstay was converted to two small loops with straight bit inbetween by two more cable ties , one close to the back-stay and one close to the cable. So no covering on the backstay and apparently better reception

TudorSailor
 
jerrytug said:
Hello if anyone could answer this slightly obscure question I would be grateful.

I'm hopefully buying a yacht with twin backstays, fitted with a SSB radio, aerial tuner etc.

The backstays are widely separated where they attach to the stern, but join the same fitting at the aft side of the masthead.

Both the backstays are insulated at top and bottom.

One of them is connected to the tuner in the lazarette in the usual way.

The other insulated backstay is not connected to anything.

I have just got a quote for renewing the 22-yr old rigging ( from a reputable rigging company) and he says there is no point in having both backstays insulated, just the one connected to the tuner.

However, I thought both might have been insulated for a reason, that being, interference/interaction between the two.

I will bounce this query off my ham club, but no meetings til next year.

Is there a good reason to insulate BOTH backstays? Cheers Jerry
Click to expand...

Most insulators are swageless fittings so easy to re-attach to new wire. And worth a reasonable sum second hand. So if they are thast sort dont let the rigger walk off with two of them.

Personally I would insulate both and then try using just one or both with a loop at mast head level to see which aerial worked best - the whole thing being a black art.
 
birdseye said:
Personally I would insulate both and then try using just one or both with a loop at mast head level to see which aerial worked best - the whole thing being a black art.
Click to expand...

I have twin backstays and before we fitted the SSB and re rigging the boat, the advice we got was to insulate both. I use only one of the stays as the aerial. The reasoning I was given was to stop the signal jumping across onto the other stay at the top where they are closest.

All I can say is that I am told we put out a very strong signal but as has been said above, this is all a bit of a "black" art
 
I cant imagine why you would even consider insulating both - you may as well insulate everything and anything in line with any aerial. There is simply do need and as good as the insulators, all you are doing is adding another potential failure point and cost. Just make sure you have the insulators located to give the best length of backstay between and the least cable run from the tuner to the bottom insulator. I have had no issues with my setup and often transmitt and receive over thousands of miles with excellent reception.

Of course if you have proof to the contrary all well and good but I think it needs to have some scientific base.
 
>So does the wire get hot or not?

I doubt anybody would be able to answer that, without doing what I did, because nobody would be stupid enough to cook their hand. However since you can light a cigarette on the wire indicates it must be hot.
 
ip485 said:
TUDORSAILOR - I dont quite folow how you had it setup and why the reception imrpoved?
Click to expand...

He's describing a method of mounting the feeder cable on standoffs a couple of inches long, rather than strapping it tight along the non-aerial lower part of the stay. A similar method I've seen is to use short lengths of plastic pipe, with a long cable tie round the wires at each end and through the pipe in the middle:

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If you simply strap the feeder to the lower part of the stay, you are connecting the two together. RF is not DC, it is not particularly impressed by the few mm of rubber between the two conductors.

Pete
 
KellysEye said:
>So does the wire get hot or not?

I doubt anybody would be able to answer that, without doing what I did, because nobody would be stupid enough to cook their hand. However since you can light a cigarette on the wire indicates it must be hot.
Click to expand...

Of course it doesn't get hot! You are putting out a maximum of 150 watts, and that's at peak power whereas on SSB you are usually emitting 1/6th of peak maybe less, so it amounts to rather less than a domestic light bulb. You can't light a cigarette from one of those, and in the SSB transmitter case the power is going into 15 metres of 10mm dia stainless steel wire: a huge thermal mass compared to a lightbulb: it would take ages and ages to make a discernible difference to the temperature, and besides you are radiating some of the power - hopefully!

I mention 'ages and ages' to point out that the thermal time constant of the backstay is long, so if you want to measure the temperature rise it's trivial: transmit for a while, turn off the transmitter (ie let go of the press to talk key) and, taking your time, go feel the backstay. It will be cold.

However the Voltage on the backstay while transmitting will be quite high, several hundred or even a thousand Volts depending on the match at the frequency in use, and several hundred Volts at RF will burn you quite nicely (ie nastily!).

As for lighting a cigarette from temperature alone, it would have to be above the burning point of tobacco, which is fairly close to dull red - you'd see it!
 
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