HF antenna cable to the backstay

[Wideocean7]

I’m hoping for some guidance with my HF aerial cable.

The background is that I will be replacing the corroded HF cable between the tuner and backstay. (I’m not sure if its’ relevant but my yacht is aluminium). When I bought her, the cable was sleeved in a flexible hose and cable tied to the backstay, with no stand-offs. Unfortunately the system wasn’t operational when I bought her so I have no idea if this set-up worked.

Many yachts seem to have the cable running up the backstay, with stand-offs of around 50mm – 75mm (2” – 3”). I don’t know how important these stand-offs are. In my case, this would be a real pain because the cable could be accidentally grabbed because the backstay is immediately behind the helm position and also next to steps down to the duck-board.

So I’m wondering about the best options. The two options I can think of are:
-Keep the existing set-up, run the cable up the backstay, with no stand-offs.
-Run the cable up the radar post – see attached photo. Here I might be able to use stand-offs (if indeed they are necessary) because the post is less likely to be grabbed.

Wise feedback would be much appreciated.
Cheers

[Brian.D]

If the backstay "is" the antenna, then you would use GTO-15 wire from the tuner to the backstay. The GTO-15 wire is insulated and looks like coax, but it is not. It is a single wire within the insulation. The connection would be made where the GTO-15 and the backstay meet.

From what you are describing, the antenna is not the backstay, but a wire that is attached to the backstay with standoff insulators. If you want, you can use insulated wire for protection.

The connection from the tuner to the antenna should not be one piece of wire, but two separate wires. This will allow for any repair work to be done if needed. You can use whatever is convenient for that connection as long as you keep it water tight. Meaning, put protection on the connection.

When measuring the antenna length, the wire from the tuner is part of the total length. i.e. the antenna is 30ft and the wire from the tuner is 10ft. Total antenna length is 40ft.

There will be some more coming on to add to this.

[Wideocean7]

Thanks for the reply Brian.D

Perhaps I wasn't clear enough. I have an insulated backstay (you can see the lower insulator on the photo). I also have new GTO 15 cable for the run between tuner and backstay connection. That cable will need to be secured either to the short section of backstay below the insulator or to the radar post. So I'm asking if stand-offs are necessary for this short run? Many in this marina seem to use stand-offs but I haven't yet heard a good reason why. It would make things so much simpler and tidier if stand-offs were not needed.

[Jim Cate]

Without the standoffs there could be some small signal loss from coupling into the "below the insulator" portion of the stay, but in practice I doubt if you would notice a difference in signal strength. I would not worry about it in your place.

Jim
N9GFT/VK4GFT

[stormalong]

I have tried with and without stand offs and did not notice any difference.

The only reason GTO-15 is used is because on the high voltage insulation. The 15 is 15 KV (thousand volts). There is no magic wire. The conductor in GTO-15 is just a copper wire. You can do the same thing by running ordinary wire through a hose.

The worry is RF burns if you are touching the wire while transmitting. With 100 watts (ham) or 150 watts (marine SSB) there is little risk of RF burns.

Brian N7BMW

[stormalong]

Originally Posted by Brian.D

The connection from the tuner to the antenna should not be one piece of wire, but two separate wires. This will allow for any repair work to be done if needed. You can use whatever is convenient for that connection as long as you keep it water tight. Meaning, put protection on the connection.

Brian D, I don't understand what you are saying about using two pieced of wire instead of one. Could you expand on this?

[Wideocean7]

Originally Posted by Jim Cate

Without the standoffs there could be some small signal loss from coupling into the "below the insulator" portion of the stay, but in practice I doubt if you would notice a difference in signal strength. I would not worry about it in your place.

Jim
N9GFT/VK4GFT

Thanks Jim - good to have such a clear reply. Cheers

[Wideocean7]

Originally Posted by stormalong

The worry is RF burns if you are touching the wire while transmitting. With 100 watts (ham) or 150 watts (marine SSB) there is little risk of RF burns.

Brian N7BMW

Stormalong - the risk of someone accidentally touching the cable whilst transmitting is definitely there. Would a standard electrical conduit reduce the chance of burns or could the plastic melt? I've no idea how one gets injured from high wattage RF.

[stormalong]

Originally Posted by Wideocean7

Stormalong - the risk of someone accidentally touching the cable whilst transmitting is definitely there. Would a standard electrical conduit reduce the chance of burns or could the plastic melt? I've no idea how one gets injured from high wattage RF.

Not standard metal electrical conduit but PVC would do. To get an RF burn the victim would have to be in direct contact with the feedline or antenna. As already mentioned the feedline is part of the antenna.

If a metal conduit was used it would act like an RF choke and really screw up your transmitted signal.

This topic has been discussed many times and the conclusions have been a 100 or 150 watt signal is too weak to do any harm. Add to that the nature of an SSB transmission, where the average RF is much lower than peak. If you were transmitting AM, FM or CW the power delivered to the antenna is continuous, with SSB the power varies with the modulation.

I have been a ham for 40 years now and have never heard of anyone getting an RF burn from a 100 or 150 watt transmission.

There is no way that you are going to melt whatever plastic insulation you choose. If you were transmitting kilowatts the situation would be different.

[Wideocean7]

Thanks for your reply Stormalong. Very helpful.

[Brian.D]

Originally Posted by stormalong

Brian D, I don't understand what you are saying about using two pieced of wire instead of one. Could you expand on this?

Sorry, now that I look at it again, "not" should not be in there. It should be a single run from the tuner to the backstay, then a connection made at the backstay. My apologies.