Radio Frequency Interference AM Radio

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Aquabelle

Aquabelle

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Jun 15, 2012
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My Fusion AM/FM radio has suffered from 'noise' on the AM band in particular since installation. I finally got around to systematically tracking down the noise sources: turns out to be mainly the Victron inverter/charger, when in charger mode..... and to a lesser degree, the engine room ventilation fans.

The 'noise' shows up via the antenna cable: unplug the antenna, the noise goes away. No noise when the unit is running off an ipod or CD player. I have a dedicated AM/FM antenna, a quality brand installed new in 2009. The antenna cable doesn't run anywhere near the inverter/charger or cabling to the engine room fans. Noise occurs in dock or at anchor, doesn't change.

I have just email'd Victron to see if there's anything I can do at the charger itself to reduce the 'noise'. I'm surprised at the Victron finding, as these units have a good reputation for RFI suppression. I am not hopeful they will be able to suggest anything.

That aside, I can most easily install an in-line noise filter in the antenna line right behind the Fusion unit. I would be very interested to hear what experience others have of these in-line noise suppressors: do they work and if so, what brand/models are recommended?
 
Last edited:
You listen to AM?
 
Have you grounded the radio chassis and/or the antenna? On our sailboat we had a ton of static until I grounded the antenna. It was an automotive antenna that I installed in a cabinet and it turned out that it was designed to be grounded by mounting it in the antenna hole in the bodywork of a car.
 
Aquabelle said:
Yep....some particular favourite talk programs. Lots of other sources for music obviously
Click to expand...

Another option, should you not be able to correct that, is Internet radio. Many stations have direct Internet feeds that can be accessed through an ap called "Tune In" or equivalent. I stream my favorites Via Bluetooth right into my radio for convenient listening of stuff I can't get locally...
 
Carolena said:
Have you grounded the radio chassis and/or the antenna? On our sailboat we had a ton of static until I grounded the antenna. It was an automotive antenna that I installed in a cabinet and it turned out that it was designed to be grounded by mounting it in the antenna hole in the bodywork of a car.
Click to expand...


Thanks Carolena: the antenna is a ground-independent type. The chassis is NOT grounded...and it doesn't appear to have provision for grounding. I too wondered about that....so now you have raised it, I will email Fusion for their comment on this
 
Heron said:
Another option, should you not be able to correct that, is Internet radio. Many stations have direct Internet feeds that can be accessed through an ap called "Tune In" or equivalent. I stream my favorites Via Bluetooth right into my radio for convenient listening of stuff I can't get locally...
Click to expand...


Steve: you are right, that would be a work-around. But it bugs me that something that should work, doesn't ! So I'm going to try to find a simple solution first...but if all too hard, that is the fall-back.
 
OK, I've ordered the in-line antenna noise suppressor (AS-100) recommended by Crutchfield at this link:


Noise suppression guide


I will report back how it works. At $10, no risk trial.


Now for the noise coming from my two engine room exhaust fans. I understand the first-choice approach to these is to fit 'ferrite suppressors' to the power supply cabling to the fans. Can anyone tell me where to fit these: right at the fan itself, or just after the circuit breakers that supply each of them? On the +ve wire I suppose??
 
When you disconnect the antenna, do you get any AM reception? You say "disconnect the antenna cable, noise goes away". The fact that you have no noise on non-AM sources doesn't matter as we are talking specific frequencies. The issue remains whether the antenna/cable are picking up the interference from the suspect devices directly over the air or from RFI emitted from the power cable. Have you tried wrapping the antenna cable in aluminum foil or similar? Anyway, the antenna in-line filters are cheap, 10 or 15 bucks over here. Try one and if it doesn't work you can take it back.
 
George: no, no AM reception without antenna...but no background hum/noise either. I can only access 6 inches or so of the antenna cable directly behind the radio....the remaining 15' would take pretty major surgery to uncover. Is it worth wrapping the first (I suppose I should say last?) 6 inches in foil?
 
Years ago I used ferrite beads to fix static on a sound system on a previous boat. You might give that a try, right now I can't remember what radio or just where they were clamped try google for information.
 
You are dealing with one of the most perverse problems in Radio Frequency (RF) electronics. External noise can enter any system through the power supply leads, into the antenna or, less commonly, directly into the electronics. Since the noise is not present when using an ipad or other source it is probably not coming in through the power supply or directly into the electronics. It is likely coming in through the antenna, appearing to the radio as just another signal. RF noise is commonly generated from florescent lights, 12V to 115 v inverters, electric motors and a host of other devices. The difficulty in eliminating this noise is the primary reason FM radio came into widespread use. There is not room here to go into the details but FM radio is much more noise tolerant than AM.

The RF noise generated by the various sources (motors, lights etc.) radiates through space, is picked up by the antenna, amplified and comes out your speaker and annoys you. Since it is in the same frequency range of the radio station you are listening to, it cannot easily be filtered out without filtering out your favorite station as well. The only real solution is to remove the source of the noise or start listening to FM like everyone else. The noise can sometimes be filtered out at the source but it is a tedious process. Turn off breakers one at a time and see if the noise goes away. That should help you determine the specific source of the noise. Depending on what it is, there are various techniques for eliminating radiated noise. I hope this helps a little.

Paul
 
Great reply Paul, thanks. I have i.d.'d the inverter/charger (in charger mode) and the two engine room exhaust fans as the noise culprits, by turning off their circuit breakers as you suggest (in fact I turned everything off and then back on one at a time; then when everything was on, did the same in reverse, turning each off one at a time)...so I can be sure these are the noise sources (with the charger being by far the worst) and the noise is coming via the antenna, not via the radio's power supply.
 
"the noise is coming via the antenna, not via the radio's power supply".

You might try using copper screen to encase the unit and then ground the screening.

A po-boy Faraday Cage.
 
An update on where I am with this issue. The antenna noise filter described at post #10 finally arrived and took about 5 seconds to install. It has made a substantial difference to the static noise problem....not completely removing it but getting it down to a point where it is tolerable to listen to the AM stations I want to access.


BUT here's the thing: in fiddling around connecting this up, I noticed that the noise was almost completely eliminated when I pushed the inner probe/male part of the antenna lead connector part-way into the female socket.....but when pressed all the way in to connect the outer part of the connector, the noise returned! So I'm guessing this means there is an antenna ground problem...is that right? The antenna is a quality marine ground-independent type: what do I need to check??
 
I think what he was saying is that you should filter the power, which is the source of the noise, not the antenna which is merely picking it up.

If your fans or inverter running causes RF noise received by your radio, then make sure both are well grounded first, then you might put a ferric ring around the DC wires or install a electrical noise filter on the devices causing the noise.
 
And to answer your other question, if you're trying to stop noise coming out of a device the ferrite should be placed as close to the device as possible.

Ken
 
Further to post #17: I have used my multi-meter to test for continuity between the central male fitting and the outer ground case, at the radio end: no continuity there so I think the co-ax is free of an internal short. I will have to wait till I have a friend on board to test continuity in the cable end-to-end: I am following the instructions provided here to test the cable:


 
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