Ferrite Beads on HF Radio Installation

[Dockhead]

Originally Posted by stormalong

Wide strap would be best. Large diameter thin wall copper pipe would be my next choice if that is possible. Wire has a small surface area unless it is very very large wire. Is it possible to cut a narrow slot through the bulkhead?. . . . I think in your situation for an optimum installation some holes will need to be drilled through those bulkheads.. . . .

I will try some 16mm2 battery cable I bought today (AWG 6).


There is one accessible spot in the bulkhead with one hole in it. I can't access any other bulkhead space without wrecking furniture in the aft cabin, which I am certainly not going to do for the sake of HF radio. Besides that, the bulkhead is mounted in a ring frame and I couldn't cut into that without a huge hassle, even if I could get to it.



I have a roll of copper strapping but there is no way to use it here.


Another concern, however, is proximity to other cables. The coax to the radio and the ground cable will have to be pretty near one another, and to various other cables. I hope this is not going to be a problem.

Originally Posted by stormalong

. . . Nothing wrong with properly crimped connectors on LMR400 since you have the crimping tool. Another caveat with LMR is that it is a foam dielectric and tight radius bends cause the center conductor to migrate towards the shield. Follow the cable specs and you are good.

I use both LMR400 and LMR superflex in my home ham shack. On the boat I use tinned RG213 going up the mast for VHF and for HF from the radio to the antenna tuner.

I would also suggest that the coax be routed separately from all other electric cables. Being in the same bundle is a good way to transfer RF into your electrical system. And keep it away from you autopilot compass sensor and it's wire too!

Thanks. I am aware of the drawbacks of LMR400 and wouldn't generally use it on the boat. This run was installed before me, as part of a satphone installation which I removed, and it was done professionally and well without any significant bends. I do have one run of LMR400 up the mast to the first spreader, for a VHF/UHF ham antenna, which I figured would be ok since it's not mission critical.

[Jammer]

Originally Posted by Dockhead

This cable has to go in the same conduit as control cables for Eberspacher heater, control cables for pilot solenoid, and rudder position sensor, also cables with power for the bathing platform hydraulics and some other stuff.

I guess I'm going to need ferrite beads on all of those? I sure hope I don't get a lot of RF in my engine room -- there are a lot of electronics in there.

Well, I would expect that's going to be something of a problem.


Read K9YC's excellent guide if you have not already done so.


HF generally requires more than a simple bead to suppress. In most cases a larger bead or toroid where the cable can make multiple turns through the window will work best. You will want to seek out 31 material as it works well at HF unlike most ferrites.


A fact to consider is that you will want to keep HF noise from your autopilot, heater, etc., out of your radio just as much or perhaps more than you will want to keep rf out of the autopilot and heater.


K9YC covers other filtering techniques you can consider e.g. capacitive and hybrid filters.

[Wotname]

Originally Posted by Dockhead

...........
I have acquired 5 meters of 16mm2 tinned marine cable, which is AWG 6, 4x the area of AWG 12, the biggest cable I can get through the conduit I have.

..................

Well, your 16mm2 cable is going to be better than AWG12 but not for the reasons you cite and not as better as you think.

It appears you are confusing cross sectional area to surface area; pardon me if I'm mistaken.

The RF characteristics are far more dependant of the surface area than the cross sectional area. In a round form, surface area equates to the circumference (RF speaking).

Looking at your example, AWG 12 has a diameter of ~2.1mm and a circumference of 6.6mm while 16mm2 has a diameter of ~4.6mm and a circumference of 14.5mm. So the RF difference between these two wires is twice or half denying which way you are looking at it.

FWIW, 16mm2 is closer to AWG 5 than AWG if you believe wikipedia https://en.wikipedia.org/wiki/American_wire_gauge

[Wotname]

Originally Posted by Wotname

Well, your 16mm2 cable is going to be better than AWG12 but not for the reasons you cite and not as better as you think.

It appears you are confusing cross sectional area to surface area; pardon me if I'm mistaken.

The RF characteristics are far more dependant of the surface area than the cross sectional area. In a round form, surface area equates to the circumference (RF speaking).

Looking at your example, AWG 12 has a diameter of ~2.1mm and a circumference of 6.6mm while 16mm2 has a diameter of ~4.6mm and a circumference of 14.5mm. So the RF difference between these two wires is twice or half denying which way you are looking at it.

FWIW, 16mm2 is closer to AWG 5 than AWG if you believe wikipedia https://en.wikipedia.org/wiki/American_wire_gauge

Opps...So the RF difference between these two wires is twice or half depending which way you are looking at it.

[Jim Cate]

^^^^^

For rf, conducted on the surface of the wires, would you not add up the total surface area of the many strands rather than just the pi x D of the bundle?

Jim

[Jammer]

Maybe, though there isn't as much current in the strands in the center of the bundle. People who are into this sort of thing argue for pages and pages on the forums, sort of like gearheads talking about motor oil. In real installations, any differences are subtle. We're dealing with HF, and only 100 watts or so.


Besides, anything much bigger or fancier than the conductor in the parallel backstay antenna will just drive the losses there, because the currents are the same.

[Wotname]

Originally Posted by Jim Cate

^^^^^

For rf, conducted on the surface of the wires, would you not add up the total surface area of the many strands rather than just the pi x D of the bundle?

Jim

Maybe... but this not in my understanding of skin effect at RF frequencies.

Perhaps if each internal strand was insulated from the others but I would still think the EM field from each internal strand would cause current flow to only occur at the outer surface of the whole cable - just like it would if the cable was solid copper.

Happy to be educated though .

[Dockhead]

Originally Posted by Wotname

Maybe... but this not in my understanding of skin effect at RF frequencies.

Perhaps if each internal strand was insulated from the others but I would still think the EM field from each internal strand would cause current flow to only occur at the outer surface of the whole cable - just like it would if the cable was solid copper.

Happy to be educated though .

Fine, but all I care about is that it works.


I had an RF ground to a throughhull via a heavier battery cable in another boat, which worked just fine.



Jammer said AWG12 would work OK.


Bill Trayfors says wire is fine.


So will it work? There is no way I'm getting copper strapping through that bulkhead.


The through-hull is a really good one -- a giant 2" one which must weigh a few kg, which will have a lot of contact area with the seawater.

[Dockhead]

Originally Posted by Jammer

. . . Besides, anything much bigger or fancier than the conductor in the parallel backstay antenna will just drive the losses there, because the currents are the same.

Does it work like that?


The parallel backstay is ordinary lifeline wire, like 4mm, stainless steel (less conductive than copper). And is 3x as long.



Bill Trayfors says we fuss too much about ground connections -- we happily connect our antennas with thin GTO 15 wire.

[Wotname]

Originally Posted by Jim Cate

^^^^^

For rf, conducted on the surface of the wires, would you not add up the total surface area of the many strands rather than just the pi x D of the bundle?

Jim

Besides Jim, if this was correct we would have all been using extremely fine stranded copper cables instead of flat solid copper strapping for the past century - unless we have all been conned by Guglielmo Giovanni Maria Marconi, 1st Marquis of Marconi and his RF goddess.

But you could be onto something!

[Wotname]

Originally Posted by Dockhead

Fine, but all I care about is that it works.


I had an RF ground to a throughhull via a heavier battery cable in another boat, which worked just fine.



Jammer said AWG12 would work OK.


Bill Trayfors says wire is fine.


So will it work? There is no way I'm getting copper strapping through that bulkhead.


The through-hull is a really good one -- a giant 2" one which must weigh a few kg, which will have a lot of contact area with the seawater.

To be clear, on paper the 16mm2 cable will be better than the AWG12. The only question is by how much.

I think the answer is likely to be "a bit but not a lot better".

Although some think RF is a black art while others thinks believe it to be a science, I think some of the time we can't know all the variables.

Does it matter it your ground water contact is near the surface or a fathom deep?
Some will argue it matters and some will argue the difference is not measurable in meaningful way...

[s/v Jedi]

I have found that copper strapping always works, always works better and always means more work.

In this case, from the lazarette, you select a path through the bilge, mark it, sand it, then glue the copper to it, then paint it and the sanded area around it with Interprotect 2000 or TotalProtect.

In case of obstructions like bulkheads, your first choice is to use a multitool with plunge blade and cut a slot for the copper. Use thickened epoxy to close it after the copper is fed through. Second choice is to bring the copper up the bulkhead a bit, cut it, and continue down the same spot on the other side of the bulkhead. Next, drill a couple of small holes, then use copper bolts, washers and nuts to make the connection to both sides.

The main reason for doing all that extra work compared to pulling a wire is not the benefit of the copper strap, but to have it in the bilge, completely separate from other wiring.
Also, this run can have a capacitive coupling to the seawater. I have a balsa cored hull, which makes this impossible, but the whole aft end of the boat has a copper mesh included in the fiberglass layup schedule so that it is close to the water, but safely inside the fiberglass, never touching the water. This is all that is needed for a perfect tuner grounding.

[Dockhead]

Originally Posted by s/v Jedi

I have found that copper strapping always works, always works better and always means more work.

In this case, from the lazarette, you select a path through the bilge, mark it, sand it, then glue the copper to it, then paint it and the sanded area around it with Interprotect 2000 or TotalProtect.

In case of obstructions like bulkheads, your first choice is to use a multitool with plunge blade and cut a slot for the copper. Use thickened epoxy to close it after the copper is fed through. Second choice is to bring the copper up the bulkhead a bit, cut it, and continue down the same spot on the other side of the bulkhead. Next, drill a couple of small holes, then use copper bolts, washers and nuts to make the connection to both sides.

The main reason for doing all that extra work compared to pulling a wire is not the benefit of the copper strap, but to have it in the bilge, completely separate from other wiring.
Also, this run can have a capacitive coupling to the seawater. I have a balsa cored hull, which makes this impossible, but the whole aft end of the boat has a copper mesh included in the fiberglass layup schedule so that it is close to the water, but safely inside the fiberglass, never touching the water. This is all that is needed for a perfect tuner grounding.

Additional penetrations of the bulkhead from my lazarette are not practical; I only have a couple of ducts through the ring frame, and that's what I'm stuck with. Strapping won't go there. Nor could I really run strapping from there to the engine room. This is a non-starter. It will have to be cable. If cable doesn't work, then I'll have to sell the HF radio and switch to satellite. But I've used cable before for an HF radio RF ground, and it was ok.

[Jammer]

Originally Posted by Dockhead

Does it work like that?

Yes.


The basic antenna serving as a starting point for understanding is a dipole, that is, two pieces of conductive material (wire, rod, tubing, etc) extending in opposite directions. One would be connected to each terminal on the transmitter.


It is possible to substitute a conductive disc for one of the pieces, with the other conductor perpendicular. RF performance is nearly identical. The ocean is electrically the same as a conductive disc, or nearly so, with the soil on dry ground being similar but less ideal (because it is more resistive).

The parallel backstay is ordinary lifeline wire, like 4mm, stainless steel (less conductive than copper). And is 3x as long.

Backstay antennas are, well, terrible antennas, particularly when used for the entire HF band. The only reason they work at all is that a sailboat in the ocean benefits from a fantastic ground plane (salt water) and a lack of man-made noise (as long as sources on the vessel itself are controlled). I have experimented with backstay-like vertical antennas on my house and can confirm this experimentally.


You can build a simple dipole for a specific band and hoist it when needed and it will far outperform (by 10dB) a backstay antenna, and at a tiny fraction of the cost. No tuner needed. No ground plate needed. No RF in the boat. And some sailors do that. But they're fiddly and not suitable to rely on in an emergency, so they aren't the established practice.

[Brian.D]

That thru hull, make sure it is thoroughly cleaned of any paint the next time you haul out the boat. The inside of the thru hull will work fine, but you also want to use the outside as well.