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Old 29-05-2021, 09:04   #1
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Ferrite Beads on HF Radio Installation

I've gotten back around to re-installing my HF radio, and there is one problem I had last year which I want to solve this year -- namely interference with my electronics when transmitting.


The ground cable (yes, I have copper strapping and know it's better, but it's impossible to route in this installation, so I'm using heavy battery cable, and it seems to work OK) runs nearby the N2K backbone and some other electronic cabling.


I thought ferrite beads might be liberally applied to this -- will that help? I supposed putting ferrite beads on the ground cable itself would be useless?
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Old 29-05-2021, 09:51   #2
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Re: Ferrite Beads on HF Radio Installation

I would think that it depends on if the interference is DC or AC related. The DC component would be related to the 12VDC or battery side. The AC component would be related to the RF side. So we would probably need to know which one.

Now, what I would do would be to put a Common Mode Choke at the input to the antenna tuner. This will keep any stray RF getting back into the radio, AND, into the "shack". You can make one your self or you can buy one. They do work as I use them on my VHF and HF stations in my home. If they work in the home shack keeping RF out of my laptop sitting right next to the radio, they should work on the boat.

Next is how is the radio tuner grounded? Gordon West recommends a seawater ground over the traditional copper ground. Now this is for RF, not DC ground. A good RF ground will also help to keep the stray RF out of the electronics.

But I think what you want to do is nip the problem at the source; that being the point of transmission, the antenna tuner.

One way to test this is to bring in a stand alone battery and connect it to the radio. Key the radio and see if the RF is still in the boat. If the offending interference is related to the boat's DC grounding, then you will know right away since the radio is no longer connected to boat's DC ground. I hope your antenna tuner is getting its power from the radio and not the battery. If independent, you might have to use two batteries then.

JMHO
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Old 29-05-2021, 11:19   #3
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Re: Ferrite Beads on HF Radio Installation

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Originally Posted by Brian.D View Post
I would think that it depends on if the interference is DC or AC related. The DC component would be related to the 12VDC or battery side. The AC component would be related to the RF side. So we would probably need to know which one.

Now, what I would do would be to put a Common Mode Choke at the input to the antenna tuner. This will keep any stray RF getting back into the radio, AND, into the "shack". You can make one your self or you can buy one. They do work as I use them on my VHF and HF stations in my home. If they work in the home shack keeping RF out of my laptop sitting right next to the radio, they should work on the boat.

Next is how is the radio tuner grounded? Gordon West recommends a seawater ground over the traditional copper ground. Now this is for RF, not DC ground. A good RF ground will also help to keep the stray RF out of the electronics.

But I think what you want to do is nip the problem at the source; that being the point of transmission, the antenna tuner.

One way to test this is to bring in a stand alone battery and connect it to the radio. Key the radio and see if the RF is still in the boat. If the offending interference is related to the boat's DC grounding, then you will know right away since the radio is no longer connected to boat's DC ground. I hope your antenna tuner is getting its power from the radio and not the battery. If independent, you might have to use two batteries then.

JMHO

Thanks, really interesting and really helpful.


I think I'm going to do this differently. I think it was a fundamental mistake to put the tuner in the salon. I'm going to rip it out and put it in the lazarette. Get all that electromagnetic action away from my nav station and instruments. I'm wondering whether I might even find a place for the radio itself (M802) which is further from the instruments.


This is a lot of hassle.
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Old 29-05-2021, 15:57   #4
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Re: Ferrite Beads on HF Radio Installation

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Thanks, really interesting and really helpful.


I think I'm going to do this differently. I think it was a fundamental mistake to put the tuner in the salon. I'm going to rip it out and put it in the lazarette. Get all that electromagnetic action away from my nav station and instruments. I'm wondering whether I might even find a place for the radio itself (M802) which is further from the instruments.


This is a lot of hassle.
Please remember the antenna tuner needs to be as close as practicable to the antenna and the RF ground.

BTW, great reply from Brian.D.
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Old 30-05-2021, 06:13   #5
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Re: Ferrite Beads on HF Radio Installation

Thanks for that.


I am moving the entire mess to the lazarette.


That brings the tuner to within 1 meter or so of the antenna (an isolated parallel backstay).


But the ground is really a bitch. The nearest through-hull is really distant -- maybe 5 meters or even more. And a strap is impossible to run to it. I understand that the ground cable will resonant and go way up in impedence if it is longer than 1/2 wavelength -- I can't get it shorter than half the 30mhz wavelength (10m).



I could do one of those sintered plates, but I really don't want to drill a hole in my fully cored hull.


So what to do? Lifelines? That would be a ca. 1 or at most 1.5m cable; could use a heavy battery cable. What do you think?
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Old 30-05-2021, 06:18   #6
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Re: Ferrite Beads on HF Radio Installation

I also have a massive stainless steel rudder shaft I could easily attach to, and which is even closer than the lifelines. Would that be better or worse than lifelines?



Bill Trayfors writes about this here: https://bigdumboat.com/LTS/ssbinstallation.html
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Old 30-05-2021, 06:20   #7
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Re: Ferrite Beads on HF Radio Installation

And last question: I have an unused run of LMR-400 cable which used to serve a now uninstalled satellite installation. Gross overkill for connecting M802 to tuner, but won't this be ok, with pretty decent shielding?
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Old 30-05-2021, 06:22   #8
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Re: Ferrite Beads on HF Radio Installation

Keep in mind that rf is running on the surface which is why copper strapping is best for the counter poise side of the radio, not wire of any sort. Moving your tuner close to the back stay is a smart move. Nothing wrong with tying in your lifelines, toe rail into the counter poise side of the radio.
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Old 30-05-2021, 06:39   #9
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Re: Ferrite Beads on HF Radio Installation

Everything from the tuner insulator onward is radiating antenna. You want as much outside as possible. Put a common mode choke/ isolator in the radio to tuner feed. Might consider the prop shaft stern tube for seawater ground connection.

I did away with my lower insulator on my backstay and could detect no signal reduction. Used pex and pvc tubing for safety insulation.


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Old 30-05-2021, 06:59   #10
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Re: Ferrite Beads on HF Radio Installation

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Keep in mind that rf is running on the surface which is why copper strapping is best for the counter poise side of the radio, not wire of any sort. Moving your tuner close to the back stay is a smart move. Nothing wrong with tying in your lifelines, toe rail into the counter poise side of the radio.


That's what everyone says, but our guru Bill Trayfors says that the strap is not necessary; wire works also:


"And, round wire works every bit as well as copper foil. Hey.... aren't dipoles constructed of wire? And aren't they effective?"


https://bigdumboat.com/LTS/ssbinstallation.html


I have a roll of copper strap, but there's no way I can use it. I can't lead it through a deck gland to my lifelines (if that's the way I go), and I can't connect it to a rotating rudder post (if I go that way) since it doesn't flex like cable. So I think it's going to be a heavy battery cable.
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Old 30-05-2021, 07:01   #11
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Re: Ferrite Beads on HF Radio Installation

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Everything from the tuner insulator onward is radiating antenna. You want as much outside as possible. Put a common mode choke/ isolator in the radio to tuner feed. Might consider the prop shaft stern tube for seawater ground connection.

I did away with my lower insulator on my backstay and could detect no signal reduction. Used pex and pvc tubing for safety insulation.


Frankly

Thanks. I considered using the regular backstay -- would be really easy to connect as the backstay chainplate is right next to the tuner. But then the whole rig would radiate, since I have no insulator at the top.


The parallel backstay solves all those problems, but it's extra windage and it's in the way, which is not good.
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Old 30-05-2021, 07:09   #12
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Re: Ferrite Beads on HF Radio Installation

The ICOM AT 140 internal ground connection is wire (I looked). Foil might be best in terms of biggest bang for the weight of copper, but large stranded wire has a lot of surface area. Short length is also a plus.


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Old 30-05-2021, 07:14   #13
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Re: Ferrite Beads on HF Radio Installation

Just so we understand... the ground side of the tuner is actually the other half of the antenna. It is not just a "ground". A true antenna requires two sides to work properly. Like a dipole or a vertical with a ground plane. An RF wave is an AC Sine Wave, so it needs a negative side just as much as a positive side.

If the rudder shaft is in contact with the water, that is a good point of connection. As for the connection, you know how a coffee pot that connects directly to the electrical base using circular rings? You can do that with the rudder shaft. Make the connection on the rudder shaft and that will be a brushing (or roller) that slides alone the copper tape on the hull near the shaft. Or something like that. Just a thought.

Do you have a vent that goes outside? You can run your wire out the vent and let it sit 6" below the surface of the water (Gordon West recommendation). A thru hull would be nice but if you don't have one... improvise, adapt, overcome.

I don't know your boat so I don't know what is what, but I am sure if you sit and think about it you will create a solution to solve the problem. No problem is unsolvable.

If you haven't seen this, give it a read.

JMHO
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Old 30-05-2021, 07:49   #14
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Re: Ferrite Beads on HF Radio Installation

Quote:
Originally Posted by Brian.D View Post
Just so we understand... the ground side of the tuner is actually the other half of the antenna. It is not just a "ground". A true antenna requires two sides to work properly. Like a dipole or a vertical with a ground plane. An RF wave is an AC Sine Wave, so it needs a negative side just as much as a positive side.

If the rudder shaft is in contact with the water, that is a good point of connection. As for the connection, you know how a coffee pot that connects directly to the electrical base using circular rings? You can do that with the rudder shaft. Make the connection on the rudder shaft and that will be a brushing (or roller) that slides alone the copper tape on the hull near the shaft. Or something like that. Just a thought.

Do you have a vent that goes outside? You can run your wire out the vent and let it sit 6" below the surface of the water (Gordon West recommendation). A thru hull would be nice but if you don't have one... improvise, adapt, overcome.

I don't know your boat so I don't know what is what, but I am sure if you sit and think about it you will create a solution to solve the problem. No problem is unsolvable.

If you haven't seen this, give it a read.

JMHO

Thanks; yes I re-read the Gorden West article. He and Bill Trayfors contradict each other about foil/strap vs. wire. I hope Bill is right because I have no way of using foil.


The Gordon West article gives me doubts about the rudder shaft. The shaft does not contact the water (or not much); I think its main principle of operation would be capacitive coupling to the sea water.



So maybe the lifelines (which I think are proven to work well?) might be the better solution.
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Old 30-05-2021, 08:33   #15
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Re: Ferrite Beads on HF Radio Installation

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But the ground is really a bitch. The nearest through-hull is really distant -- maybe 5 meters or even more. And a strap is impossible to run to it. I understand that the ground cable will resonant and go way up in impedence if it is longer than 1/2 wavelength -- I can't get it shorter than half the 30mhz wavelength (10m).

So what to do? Lifelines? That would be a ca. 1 or at most 1.5m cable; could use a heavy battery cable. What do you think?

If you want good, reliable HF performance then get a sintered plate and install it the next time you haul out. Using a thru-hull is a compromise. Using lifelines is a compromise. Will they work? Sure, sort of, in a Rebel Heart sort of I-tested-it-once-and-got-50-miles sort of way; you'll end up with a directional pattern that works at some frequencies but not others. Backstay antennas are highly dependent on ground quality.

Don't obsess over strap vs. wire. Use strap where you can.

If serious about 10m make a separate antenna for it. The backstay is too long to work well at 10m. Using something else for 10m will make the length of the ground wire less critical.

Quote:
Originally Posted by Dockhead View Post
And last question: I have an unused run of LMR-400 cable which used to serve a now uninstalled satellite installation. Gross overkill for connecting M802 to tuner, but won't this be ok, with pretty decent shielding?

It will be fine as long as it stays dry if you can live with the stiffness and high minimum bend radius, and if you have the correct connectors and crimping dies. LMR-400 uses aluminum foil and copper braid and will corrode more quickly in the salt air than other types. I would use RG58 and give the LMR400 to someone who wants to use it on land.


Quote:
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Thanks. I considered using the regular backstay -- would be really easy to connect as the backstay chainplate is right next to the tuner. But then the whole rig would radiate, since I have no insulator at the top.

The parallel backstay solves all those problems, but it's extra windage and it's in the way, which is not good.

The thing about parallel backstays is that they are capacitivly and inductively coupled to the uninsulated backstay to which they are attached, so the antenna performance is no better than using the uninsulated backstay itself.


My advice is as follows:
  1. If you are serious about HF, get a dynaplate and insulate your backstay.
  2. If that is untenable, ditch the parallel backstay antenna and just use a backstay chainplate bolt as your antenna connection. Insulate accessible portions of the backstay for crew safety. You will have less windage and it will work just as well and look better.
  3. If you decide not to solve your ground problem, then make or purchase 1/2 wave dipoles for the band segments at 20 meters and above that you want to use. Hoist these from a flag halyard or whatever when needed and connect them straight to the radio with no tuner. There are some nice, clean designs out there where the antenna and feedline replace the core of a double braid rope.
Much depends on your goals. HF in this modern age is usually used for a reason. The compromises that will be acceptable and techniques that work best will be different depending on whether you are relying on HF as a primary means of communications with distant shore stations, using it for over-the-horizon comms with buddy boats, or trying for an occasional high-quality connection back home when the bands open up.


Oh, and ferrite beads on the ground connection alone would probably make matters worse because they would increase the ground impedance. They would also get hot, possibly hot enough to become a hazard, depending on the material used and various other factors.
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