Backstay Insulator

[Tim Good]

Forgive my ignorance but when you have a backstay with an insulator in it, is that for us with SSB or something similar?

My boat (relatively new to me) has an insulator and then a small black cable running up it and connecting to the wire just above the insulator. What number of things could that be for? In fact the black cable has a black box on the end of it also which was clipped to the backstay with a jubilee clip.

 

[William_H]

Yes the backstayw as being used as an antenna. Mostly this is for SSB HF 2 way radio. However it could also be used for LW/MW AM radio reception or low frequency weather fax type signals. The real question is what is the balck box and where does the wire go to after the box? I think it is too small to be an auto antenna tuner as used with modern HF SSB radios so might be an active amplifier for a receiver. That strap if it is stainless steel would have been for mounting but if of brass or copper then typial of HF SSB antenna tuner earthing connection.
I reckon that in practice you will disconnect the box and find if any service you want does not work. Probably not. good luck olewill

 

[typhoonNige]

I'm no expert on SSB but I do have one with the backstay as an antenna. For this to work there needs to be an upper insulator too.

 

[Neeves]

If an SSB the antenna tuner is normally quite large 300mm x 15mm x 7mm and though they can be waterproof they tend to be mounted inside (and out of the way). The tuner will also need to be earthed and this is commonly achieved to an external earth plate, bolted outside the hull. The bolts for the earth plate will then be connected to a pretty hefty copper tape that would be connected to the tuner. Alternatively the keel can be used as the earth - but you would still need that hefty earth tape (a band of copper, ours is about 30mm wide but thin). If the keel is the earth the copper tape would normally be bolted to a keel bolt (so you would have an extra nut on one keel bolt and the copper tape, unless it has been removed). So if an aerial for an SSB there should be that earth tape somewhere down in the bilges and you might also an earth plate on the hull when you next come to slip. When used the earth plate should not be covered in AF (though not sure why as the keel would have an AF coating). An SSB has a hefty power requirement, compared to most other items on a yacht (windlass and electric winches excepted) and there could have been a dedicated power terminal with circuit breaker (which might have been since used for something else). It would be unusual to have the SSB at the helm - again if it was installed it would be at the nav station and there might be holes for the bracket.

When we raced our SSB was removed for inshore races and only re-installed for ocean races (simply left all the cables) - it was too expensive to have wet spinnakers thrown over it every weekend.

I cannot speculate what the small black box might be that you have.

We find our SSB, here in Australia, of value. its is excellent for weather forecasts (which are broadcast every 4 hours) as Australia does not have total coastal VHF coverage with forecasts, we do not 100% mobile coverage either (though close) and we do not have a sat phone. It is also useful for keeping in touch with other yachts and some shore stations geared up to provide a safety net for yachts. So SSB is very last century (we have one now because we needed it for ocean races) - but still has uses and unless its an inconvenience I'd leave as is - someone might want it in the future.

Jonathan

edit

It is possible to buy a mobile phone amplifier, connects to an external aerial port on some phones. They are common in America (where they can be sourced) but banned here in Oz and NZ. The ban extends to Australians selling them to use in Australia, but you can buy them from NZ to use here (but the use is illegal - but difficult to police). They are said to extend coverage to a couple of hundred NM, but that might be hype. I hear they are good offshore but if you use them, locally, the signal is so strong it interferes with the reception for anyone else nearby. These amplifiers need an aerial (but I thought specific type) and power. If your previous owner was 'into' communication in isolated places that might be what your black box is - though why its located near the, possible, SSB aerial - I'm not an aerial expert. I would have thought the black box would have had a name moulded into it - which would be a better clue.

close edit

 

[MM5AHO]

I use SSB aboard too, and the descriptions above sound right to me. A cable connected just above the lower insulator on the backstay is the "feed" to the antenna (which is the backstay). That cable typically goes to an antenna tuner, as described by others. The black box in your pic looks too small to be that. It might be simply a join in the cable, waterproofed by installing in a box. Opening it might suggest its purpose.

Digressing, on mobile phones: The distance that most phone systems will work over is limited, but not by signal strength either way, but by the time it takes the signal to get between bast station and handpiece. Exceed that distance and the protocol will fail, as it takes too long to get the reply that the comms protocol was seeking. I made an antenna for mobile phone use once and ran into this problem at about 40 miles. Good signal strength, but no data comms.
Wifi is different, in that it doesn't have that "handshaking". Distances of several hundred km have been achieved on wifi.

 

[Bilgediver]

I use SSB aboard too, and the descriptions above sound right to me. A cable connected just above the lower insulator on the backstay is the "feed" to the antenna (which is the backstay). That cable typically goes to an antenna tuner, as described by others. The black box in your pic looks too small to be that. It might be simply a join in the cable, waterproofed by installing in a box. Opening it might suggest its purpose.

Digressing, on mobile phones: The distance that most phone systems will work over is limited, but not by signal strength either way, but by the time it takes the signal to get between bast station and handpiece. Exceed that distance and the protocol will fail, as it takes too long to get the reply that the comms protocol was seeking. I made an antenna for mobile phone use once and ran into this problem at about 40 miles. Good signal strength, but no data comms.
Wifi is different, in that it doesn't have that "handshaking". Distances of several hundred km have been achieved on wifi.

Some f the folk here are still using analogue phones in their countries so the ARQ problem does not exist. We regularly got 100 miles range using the old analogue phones between offshore rigs in the southern north sea and shore using wee beam antennas.

 

[Martin_J]

My guess is that the little black box in your hand contains a simple 9:1 unun...
It will allow the connection to be made from the 50 ohm Co ax to the single wire backstay antenna.
Most marine ATUs (Antenna Tuning Units) have this built in and you can then connect a random length wire e.g your backstay directly to it.
Other non marine ATUs will perform the same tuning function but will have a 50 ohm Co ax presentation for both rig and antenna.

 

[Martin_J]

Unun. ... strange word. Could be written Un-Un.... or Unbalanced to Unbalanced.

 

[Tim Good]

Unun. ... strange word. Could be written Un-Un.... or Unbalanced to Unbalanced.

Thanks all. Previous owner was a tech junkie and did mention of a mobile amplifier and there is an Inmarsat Terminal which I'm yet to remove. I'll else the wire in place at least as a mousing line.

 

[NorthUp]

"Balun"

 

[Neeves]

For those with an interest in mobile signal enhancement offshore you might like to look at products under the Cyfre brand. As mentioned above these are not legal in Australia. These look just like the little box in the OPs early post - but then lots of items look like that little box! From memory you needed compatible cables and an aerial/antenna (which look like a beefy VHF antenna). The amplifiers were phone or provider specific (and, then, they plugged into an aerial socket on the mobile phone). Ericcson used to sell, may still do, something 'similar' which was legal but then it was quite pricey.

Jonathan

 

[KellysEye]

As said a SSB installation has an insulator near the bottom and top of the mast, I've seen dozens of boats with SSB but never seen a black box anywhere near the backstay. The ATU is normally inside. Our tuner wasn't earthed the radio has an earth jack point.

>there is an Inmarsat Terminal which I'm yet to remove

If it's Inmarsat C keep it it great for free weather forecasts, as is SSB, and incoming short emails are free. Also it has an emergency button that connects to the nearest satellite which is much quicker the using an EPIRB. We had one and after the windvane it was the best bit of kit on the boat.

 

[Neeves]

Kelly, Now that you mention it our radio might have had the earth, not tuner. Our radio and tuner were adjactent to each other - but we had a remote head at the nav station witb a fibre optic cable connection to the radio itself.

 

[KellysEye]

> Our radio and tuner were adjactent to each other

The ATU should be as close to the exit point inside the boat where the wire is that connects above the insulator. Also the transmission wire should be connected to the ATU by coppper foil. Also bear in mind that the ground makes up half the aerial so the better the ground the better the signal. Metal boats have the best signal and the other boat we met with a strong signal was an American Cat that had copper foil built into both hulls.

The bottom line is it's not easy to get the best signal and the majority of boats with SSB don't have that but it's not a big problem. A strong signal gives the maximum range on a frequency but if you go up frequencies the range increases anyway so the problem of lack of strength is solved.