RFI Nois

As I understand it RFI is essentially is noise that is superimposed as a disturbance or a voltage transient on equipment. It can be impressed on the entire boat electrical power supply, or on data and signal lines that carry your GPS or navigation data between each other. This noise is then processed along with all the good data, and it will corrupt or degrade the processed information.

That being said.
After installing a new GPS and Radio.
*I now have a humm in my radio.

What would be the easiest way to track this down to eliminate the hum from my new radio?

SD

SD, I guess I'd start with the grounds, since that is usually a good place to look.* After that, depower everything, turning devices and circuits back on one at a time to see if you can reintroduce the hum.* Flourescent lights onboard?* The ballasts are notorious for generating EMI/RFI.

Do you think it could be Induced coupling interference?
*
Where*I may have electrical wires installed in parallel with other wires.

I am just thinking about possible issues to check on when I go to the boat this weekend.

I may have a Parallel run of my signal cable with my main power wiring.

SD

Delfin wrote:Flourescent lights onboard?* The ballasts are notorious for generating EMI/RFI.

Click to expand...

Thes lights turned out to be the culprit on my boat.

*

skipperdude wrote:

Do you think it could be Induced coupling interference?

Where*I may have electrical wires installed in parallel with other wires.

I am just thinking about possible issues to check on when I go to the boat this weekend.

I may have a Parallel run of my signal cable with my main power wiring.

SD

Click to expand...

Possible, and you can check out that theory by moving the wires and seeing if the hum changes in tone.* You should also check the wiring to the antenna and make sure what you have is matched to the new radio, and that if you have installed new coax the fittings are properly grounded.* A lot of times this is a process of elimination, but it is possible the radio has an issue as well.* If you still have the old, can you swap it out and see if the problem persists?* If not, you have the solution.

*

As Carl on Delfin says, shut things on and off and see what happens.* We have found the inverter/charger can be a major source of "noise".** That would be my guess if you are plugged into shore power.

I was told that the best tool for tracking down the noise is to use a battery powered *AM radio.
The idea being that by holding the radio close to subject wiring and components that the radio will pick up the interference right away.

Lets say I track down the noise what is the best way to supressit.

I was* told something about crossing the wires at a 90 deg.

Or filter or capacitor of some sort.

SD

-- Edited by skipperdude on Wednesday 9th of March 2011 11:46:16 AM

-- Edited by skipperdude on Wednesday 9th of March 2011 11:47:37 AM

skipperdude wrote:

As I understand it RFI is essentially is noise that is superimposed as a disturbance or a voltage transient on equipment. It can be impressed on the entire boat electrical power supply, or on data and signal lines that carry your GPS or navigation data between each other. This noise is then processed along with all the good data, and it will corrupt or degrade the processed information.

That being said.
After installing a new GPS and Radio.
*I now have a humm in my radio.

What would be the easiest way to track this down to eliminate the hum from my new radio?


After many years in the electronics field, the word "hum" to me, is a 60 hz, low pitched sound, much like a human would make when "humming" a tune.

So - do you have a hum or do you have something better described as "static"?
What brand and model GPS and radio?
Does the noise go away if you turn the GPS off?
Is it only on certain channels or all of them?
Did you change any other wiring or just replace the existing GPS and radio using the same wires?

Click to expand...

*

rwidman wrote:


After many years in the electronics field, the word "hum" to me, is a 60 hz, low pitched sound, much like a human would make when "humming" a tune.

So - do you have a hum or do you have something better described as "static"?
What brand and model GPS and radio?
Does the noise go away if you turn the GPS off?
Is it only on certain channels or all of them?
Did you change any other wiring or just replace the existing GPS and radio using the same wires?

Click to expand...

*

I installed a Garmin 4208 with a camera and a connection to the flat screen TV.
With a new Icom M422.

All new wiring except for the antenna coaxel.

I just noticed the humm.**More of a buzz as*I was shutting things down after my crab trip.

I think everything was off but the radio. But I can't be sure.
*
Damm old age sucks.

Note to self make a note to self.

*Oh yea. I also hooked up the DSC between the GPS and The Radio.

My Garmin 5208 causes noise on channel 68 on my VHF. I verified that it also causes noise on a handheld and a portable AM radio. I'm working on it.

-- Edited by rwidman on Wednesday 9th of March 2011 12:49:18 PM

Great.**We can compare notes on monday next.

I think the channel I was on was 16.

SD

You might want to try snap on ferrite chokes where the power leads enter the radio. It could be some sort of ground loop.
Bill

Billylll wrote:

You might want to try snap on ferrite chokes where the power leads enter the radio. It could be some sort of ground loop.
Bill

Click to expand...

That's not a ground loop.* A ground loop is where the grounds of different pieces of equipment are grounded at different places, resulting in a different potential and current flow from one ground to the other.

In the case of my plotters, the noise is eminating from the units themselves, not the power leads.* I have placed multiple chokes on the leads without effect.* If I hold an AM transistor radio near the screen of the plotter, I will hear the noise in the radio.

*

Billylll wrote:

You might want to try snap on ferrite chokes where the power leads enter the radio. It could be some sort of ground loop.
Bill

Click to expand...

I found the source it is my refrigerator.

Now how do I stop the buzzzzzz!!!

SD

*

skipperdude wrote:
I found the source it is my refrigerator.

Now how do I stop the buzzzzzz!!!

Click to expand...

Stop opening the door so often to get more beer....................Arctic Traveller

*

skipperdude wrote:I found the source it is my refrigerator.

Now how do I stop the buzzzzzz!!!

SD

Click to expand...

What type, voltage, etc.?

*

I'd have to get the book. *it's on the boat.

It's just a Norcold 12 volt fridge. It also runs on 110 when hooked to shore power.

If this is not really going to interfere with radio reception I may try to ignore it.

It does keep the beer cold.

Trading one buzz for another

I need to see if it interferes on 12 volt or just 110.

I may just live with it.

There's just no beat. Can't dance to it.

SD



-- Edited by skipperdude on Monday 14th of March 2011 09:29:13 PM

Do as you suggested and try to figure out if it is on AC or DC that the noise is created.
It may have to do with where the power is wired to it if it is noisy on DC.

The controller box on the some Danfoss*units will cause a hum on the VHF radio.* I had an Adler Barber with a 15 year old Danfoss and the radio was all but useless when you transmitted on it.* Adler Barber was aware of the problem but their only fix was to put chokes on the line. They said the signal was coming through the 12V+ side.* That didn't work.

You might try a separate 12V battery and connect the radio both + and - to it to see if that is the problem.*

I installed a new cooling unit and the problem went away.

If you're trying to filter out RFI with chokes, etc., you want to put them as close to the source (in this case, the refrigerator) as possible. Also, make sure the refrigerator frame is grounded.

skipperdude wrote:



It does keep the beer cold.

Trading one buzz for another

Click to expand...

Clearly you have your answer.* Drink enough beer so that you can't tell where the hum is coming from - your brain, or the radio.

You said that the unit will run on both 120 vac and 12 vdc.* Is that through the ship's inverter, or are you saying there is a separate inverter on the Norcold?



*

The older Norcold have a two transistor inverter, relay and a multistep transformer to run from either AC or DC. I have one but it does not , that I'm aware of, cause any noise detectable by my VHF.
My VHF though has its own power supply from one battery set, the fridge has its own power supply from a different battery set and the wiring run is separated to a good degree.
That may be part of the reason I don't have a noise problem from the fridge.
Take a look at the wiring and if they are fed from the same terminal strip somewhere try separating them , including the ground side, even temporarily as a test.

These old fridges can be tuned up a bit. Do you run it on AC periodically? Try plugging it onto AC when it is running on DC. If you hear a change in the motor noise, such as a speed up, then there is a adjustable resistor that needs to be twiddled to get the frequency up again. Be carefull. If the frequency has fallen off it may increase the noise or the ability to hear it. The freq. fall off will also affect the cooling of the fridge and not for the good.

C lectric wrote:

The older Norcold have a two transistor inverter, relay and a multistep transformer to run from either AC or DC. .................

These old fridges can be tuned up a bit. Do you run it on AC periodically? Try plugging it onto AC when it is running on DC. If you hear a change in the motor noise, such as a speed up, then there is a adjustable resistor that needs to be twiddled to get the frequency up again. Be carefull. If the frequency has fallen off it may increase the noise or the ability to hear it. The freq. fall off will also affect the cooling of the fridge and not for the good.

And how old is that technology?* Something Fred Flintstone designed?

Seriously, I've read a lot of stories on how the dual voltage refrigerators operate and I'm not sure who or what to believe.* I'm assuming they are doing something different now, but what and starting when?

Click to expand...

*

MOre like Barney.

My version is a 1977/78. Norcold used that power design for a long time. I don't know if or when they quit. I found the schematic on the back of my fridge many years ago and using it have managed to keep it tuned up.

It is slated for replacement and darn near was done this year. The fridge works well still BUT its replacement will be much bigger and use the Danfoss system along with better insulation.

I don't know what other mfgrs. of the period used so can't comment although for the period I don't think they were any better/worse untill the Danfoss came along.

My DE-490 is still made, looked online, although I can't tell if the same power module is used, likely not. At some point I'll check as I downloaded the parts list. Thetford seems to have put manuals and parts list online, nice change from before.

Using a Ferrite choke right at the source (the switching supply for the old Norcold) and grounding the frig should take care of the problem. I use a newer Norcold DE0061 dual voltage unit. I always run the unit off it's DC power it does not induce common mode RF noise into any of my systems. As far as chartplotters they are probably MFD's so by design emit some RF from the microprocessor. I use a receiver like device from a telco toner kit (you can get them from Home Depot or Lowes) I find this to be a great way to find common mode noise sources.
At least you found the problem another thing you could try is if you don't use the frig on AC disconnect the plug and see if the interference goes away. The switching supply in these units can backfeed (on the DC side) I have seen it in the past when helping another slip neighbor track down the same issue you had.
Bill


-- Edited by Billylll on Sunday 27th of March 2011 08:08:39 AM

Billylll wrote:
*I use a receiver like device from a telco toner kit (you can get them from Home Depot or Lowes) I find this to be a great way to find common mode noise sources.

Click to expand...

*Great idea, I already have one but have never thought of this use.* I wonder if it could help me find how R.F. is getting into my autopilot.* My VHF, and my SSB both will cause the autopilot to go hard over.* I've tried chokes in several places, but it still does it.* I've also carefully checked my ssb grounding foil and both connections are clean and tight.* Any ideas?...................Arctic Traveller

*

With my SSB I ended up going with two of the largest DynaPlates and doing their connection to the auto tuners ground using 3" wide copper foil. In addition I had to move the HF SSB antenna and tuner away from my electronics locker and install multiple chokes on the affected devices as well as the power supply leads at the back of the HF transciever. I swapped my large VHF primary antenna location with the SSB 23' Marine grade antenna. It was a real pain in the you know what but now I dont interfere with any of the electronics on the boat and the radio performs better because it has less noise.

Bill


-- Edited by Billylll on Monday 28th of March 2011 02:55:11 PM