VHF Radio Interference

Having an issue with our two VHF radios. We have two standard horizon GX6000 radios. When we transmit on some channels on one radio we will clicks or interference on the other. The weird part is that it only happens on certain channel combinations and not others.

The two VHF antennas are mounted like 8' apart. I am thinking of trying to put some ferrel snap cores around the antenna wires but, not sure what else could be causing the issue.

Have you spoken with Standard Horizon? I have found them to be helpful in the past.
(800)767-2450
With 2 SH radios there shouldn’t be any finger pointing.

Cigatoo said:

Have you spoken with Standard Horizon? I have found them to be helpful in the past.
(800)767-2450
With 2 SH radios there shouldn’t be any finger pointing.

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X2

The antennas are 8' apart but how close are the transceivers to each other? They could be interfering with each other if they're side by side.
If they're close together, try swapping antennas &/or power cables & see what happens. Maybe try removing a radio from the mount and temporarily relocate it to see if the issue persists. You could also tie a lazy figure 8 know in the antenna cable close to the radio if you have enough slack and make sure you don't have a lot of excess antenna cable coiled up behind the radio.
On our boat, we have one radio and respective antenna on one side of the bridge and another on the other side and one will sometimes bleed over to the other on some channels but it's not that big of an issue to me to worry about.

Thanks Shawn. The radios are about 4 feet apart. I do have about 6-10' of excess cable coiled from both antennas sitting at the bottom of our mast. Nothing behind the radios themselves. The two antenna cables do run through the same conduits from our pilot house all the way to the top of the mast. So there is a long cable run in close proximity but, I would expect that there should be no leakage past the shielding on the cables.

I called Standard Horizon and except for the ferrite suggestion they were not a lot of help. The tech I talked with however was not their primary marine guy. I was thinking after the ferrite I ordered arrived if I still have problems calling SH back.

scurvydog_pnw said:

Thanks Shawn. The radios are about 4 feet apart. I do have about 6-10' of excess cable coiled from both antennas sitting at the bottom of our mast. Nothing behind the radios themselves. The two antenna cables do run through the same conduits from our pilot house all the way to the top of the mast. So there is a long cable run in close proximity but, I would expect that there should be no leakage past the shielding on the cables.

I called Standard Horizon and except for the ferrite suggestion they were not a lot of help. The tech I talked with however was not their primary marine guy. I was thinking after the ferrite I ordered arrived if I still have problems calling SH back.

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Are the radio chassis tied to ground?

psneeld said:

Are the radio chassis tied to ground?

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That is a good question. The answer is no. I asked SH horizon that same question and got a very squishy answer. I was not sure if that was because the engineer I talked with really did not know but, he relayed it was mainly for lightning strikes.

The manual provides zip for guidance on that. In our boat we do NOT have a separate ground plane so the only option would be to tie it back to the DC negative bus.

This is one area of VHF radios I don't have a clear picture on.

Along the way, I was told chassis grounds were often used to bleed off RF that the shields in coax cable blocked from the actual transmit wire(s).

I can neither confirm or deny....but worth a try.

Which ultimate leads to any bonding system you have. While not great as the DC neg system may introduce more than reduce interference.

Check antenna connectors, particularly the shield connection. Putting a ferrite in the power supply lines would reduce HF coupling via power supply. If you have a scope look at the power line on second VHF when you hit transmit on the first. Clicking could indicate a momentary supply issue.

These things can be tricky to troubleshoot. Does it happen both on 1W and 25W output? I was on a boat where transmitting on high would set off the nearby Cummins engine panel alarm.

I’ve got 30 years in the 2way business, and i’m not sure that effect is all that unusual. The victim receiver is getting a massive in-band overload. Do both units do the same?

ARE the radios and antennas properly grounded?

The very first thing I would do is with nothing changed, go look around and see there are any LED lights on, in the boat. If there are go around and turn them off and see if that makes a difference. If it does, then that is your problem. This was the cause of our poor radio signal as well as reception. Some LED lights are better than others. We dealt with it by going around the boat and switching off lights.

Jim

JDCave makes a good point about LED lights as sources of noise. The internal high frequency switching often produces radio frequency noise which can affect radios.

Not all LEDs are like this so if yours appear to be the problem then look around for those that do not radiate noise. It may just be one or two lights that are the problem.

My FM radio is affected by the LED lights in my boat. Actually just one LED. Of course my interference is not the VHFs but the LEDs do produce noise. To boot in my case my VHFs may not be affected because we don't run with any of the LEDs operating.

scurvydog_pnw said:

Thanks Shawn. The radios are about 4 feet apart. I do have about 6-10' of excess cable coiled from both antennas sitting at the bottom of our mast. Nothing behind the radios themselves. The two antenna cables do run through the same conduits from our pilot house all the way to the top of the mast. So there is a long cable run in close proximity but, I would expect that there should be no leakage past the shielding on the cables.

I called Standard Horizon and except for the ferrite suggestion they were not a lot of help. The tech I talked with however was not their primary marine guy. I was thinking after the ferrite I ordered arrived if I still have problems calling SH back.

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I see the bolded as the possible problem. Two wires running parallel will send a signal, a coil more so. Can you put some distance between the two coils
.

Further to the LED issue, I was told a filter could be fitted, but it was never clear to me if this was on the power source or the antenna. It’s one of those “round to-its” that I never got around to pursuing.

Jim

I would investigate if u could either raise or lower one antenna. As it is, you are just a wavelength apart, with gain antennas, face to face. Coupling a lot of power, antenna to antenna. Prolly injecting a significant power level into the in band receiver. That is sub optimum.
The 6000 has fairly decent receiver specs, what we call a 80dB receiver on IM and spurs. But u are pushing the envelope here, IMO.

Hey folks. Not likely LED as I have seen the issue with no LED lights on the boat. It has been this way since installation. I do have some type 31 ferrite cores on the way to see if that helps. The antenna are on spreaders on our mast. The way the mast is constructed moving for vertical separation is not really an option. I am worried as I eyeballed it closer on the distance after Diver Dave's comment. Distance may be closer to 7'ish. That puts it pretty close to the 6.2' wavelength for marine VHF.

What is strange is that if one radio is on 16 and I transmit on 68 you hear the clicking on the other radio. Move to channel 69 no issue.

Really appreciate the help!

Not too optimistic on the ferrites, but if the intention is to block/absorb 150MHz, then type 61 is a better mix. 31, above 100MHz losses effectiveness pretty quickly.

31 is very effective from 1 to about 100MHz.

My friend has called me to his ha shack in his house several times for antenna issues.
Our first step was to simply disconnect the antenna from the radio clean it and re-install it and in 99% of the cases the issue is gone.

This is is on antenna leads that don't get moved around.
It maybe just the vibration and moist conditions are causing a poor connection on the shield.
The PL-259 connector with the So-239 socket make a really a poor connection.
Try disconnecting, cleaning and reconnecting.
Might just work.

diver dave said:

I would investigate if u could either raise or lower one antenna. As it is, you are just a wavelength apart, with gain antennas, face to face. Coupling a lot of power, antenna to antenna. Prolly injecting a significant power level into the in band receiver. That is sub optimum.
The 6000 has fairly decent receiver specs, what we call a 80dB receiver on IM and spurs. But u are pushing the envelope here, IMO.

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I agree. Although 8' is well outside the NMEA suggestion of 4' separation for VHF antennas, that would be the first place I would look. Several manufacturers make extensions that have the appropriate threads on the ends so you can just screw them on and raise one antenna.



The second place to look would be the antenna cables running parallel. In some cables, the sheath -- the outer conductor -- is a braid, which has small holes in it as it criss-crosses. This will leak a little. In the best cables the braid is supplemented with a metallic film winding that completely seals the cable. Try pulling one of the cables and running it temporarily to the radio not parallel to the other. If this is the problem, either reroute the cables or replace them with LMR-400 or another high quality cable (or both).


Jim

I use the LMR400 at home, driving with a kiloWatt. I’ts almost unmatched for loss in that size range. I’ve not heard good things about its life in marine environments, or even coastal, though. The use of thin aluminum foil doesn’t do well against salt.
When i replace my sailboat coax, it will likely be Something like Belden 9914. Tinned copper shields, and sized like RG8.

I'm not expert, but at Panbo.com, LMR400 is the go to solution for tall sailboat masts where the offshore racing rules require very low loss.



Jim

The racers want low weight aloft, thus the aluminum and lots of air space in the dielectric. If u want longevity, different rules would apply.

So I put on the ferrites on both the power wire and antenna cable as it entered into the radio. Those had not effect on the symptom. I finally got back to port where I could get a ladder and measure the span between antennas. It' 44" which is about the max spread I can do on my mast. My guess is the issue has to do with how close the antennas are to each other. Each antenna cable does have a coupler in it do to the run but, each of those is wrapped in butyl and electrical take with more ferrites now.

Not sure there is much that can be done I expect at this point as I cannot get a larger antenna separation.

I have two VHF's with antennas 4 feet apart and the cables running the same path. I twist the cables together until they separate to go to their respective antenna and I also separately twist the entire length of the positive and negative power wires to each. They work fine but you shouldn't have them on the same channel at the same time, but why would you.

scurvydog_pnw said:

It' 44" which is about the max spread I can do on my mast. My guess is the issue has to do with how close the antennas are to each other.

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scurvydog_pnw said:

Thanks Shawn. The radios are about 4 feet apart. I do have about 6-10' of excess cable coiled from both antennas sitting at the bottom of our mast.

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Ok, I'm no VHF expert but HAM dabbling decades ago made me think about the heights of the antennas, in relation to each other AND the length of cables feeding them. Something about actual real-world dimensions of wave lengths (~6ft for VHF, iirc?) and how it relates to the total cable length. I'd wonder if that excess is part of the problem. That and (as others have mentioned) there are such things are screw-on extenders, and using one on one of the antennas might move it enough reduce the problems.

A VSWR tester on the cabling might also give you more info and point to solutions. But I've never used one myself.

https://shakespeare-ce.com/marine/product/art-3-tester/

4’ ext mast on one antenna? Or did i already ask that one. Sorry. Hot bahamas is a distraction!

Soo-Valley said:

I see the bolded as the possible problem. Two wires running parallel will send a signal, a coil more so. Can you put some distance between the two coils
.

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Yes this was a good idea. One of my tests was to pull the coils apart and separate and pull the excess cable out of the bottom of the mast so there was no coil AND some path separation. No benefit. but, great idea!

Here is some basic info:
Coax relies on the center conductor current being opposite and equal to the "inner shield" current. That means the magnetic fields are cancelled and no (or not much) coax radiation, EXCEPT for the potential issue of the antenna causing some "outer shield" current NOT balanced by the intended currents. That will radiate, and is typically undesired. It is stopped by common mode chokes AT the antenna base. Could be a simple coil of the coax or the use of ferrite, such as mix 61 for vhf. Ferrite at the radio is not called for. Twisting one coax with another coax is not called for.
Twisting the TWO power wires, plus and minus is generally a good idea, but usually not necessary.
But what is going on here is the intentional radiator, the Tx antenna, is far away the most powerful source of the signal. And, its being blasted into another, resonant VHF antenna nearby. Either that has to stop with better spatial positioning, or the victim receiver needs better spec for RF blocking. And, that could be tough. The front end RF filter will likely not provide any attenuation to a signal just 1% away. The entire marine VHF voice band is about that wide. So, the RF gain circuit is getting hit with high levels of off-channel, but very strong voltage levels. It goes non-linear, making dozens of unwanted additional signals inside the receiver. One or more of those makes it to the speaker as unwanted noise, clicks, or even a reduction in intended channel sensitivity. Its akin to pulling out a splinter in your own finger, while someone is hitting you with a baseball bat. Not optimum!

diver dave said:

\ Its akin to pulling out a splinter in your own finger, while someone is hitting you with a baseball bat. Not optimum!

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Lol. That brought a smile to my face.

Dave that is really what I thought as well that the antennas are too close and it is blasting the adjacent antenna. Even on the TX antenna set at low power I still see the issue.

I did put two mix31 on both cables at the base of the mast. I was not really able to find a snap on mix61 online. Given that I have two antennas/vhf for redundancy I am either unwilling to do vertical separation OR the mast is not setup for for horizontal spacial separation.

This is really my type "A" engineering personality coming through as I can avoid the issue now that I know which working channels crosstalk with 16.

Thanks for the post!