RFI interference--How to eliminate???

[cknizeski]

Originally Posted by ResQguy

That right there should be changed. Connect the ground to chassis ground as close to the radio as possible, not the battery. Connecting anything directly to the battery's negative terminal invites not only noise but a possible return path thru your radio should the main ground lead become loose.

There is different thoughts on that. I was always told it is better to go directly to the Battery with the ground, but to be sure to fuse the negitive to prevent it from becoming a return path back to your radio.

This is from K0BG's web site an extremely informative site on all aspects of a mobile install including noise elimination Wiring & Grounding

KØBG.COM

"Although there are two schools of thought with respect to where the power cable ground of an amateur transceiver should be connected, all agree that the chassis should not be used as a ground return. While this practice was wide-spread in the past, doing so in a modern vehicle should be avoided at all costs. It is important to remember that today's vehicles are rolling computers, with some models having as many as 50! Each one of these CPUs has sensors connected to it which control every facet of operation. Using the chassis for a ground return can cause a ground loop to occur which can corrupt the data read from them".

[hertzian]

Originally Posted by ozzie

I have installed ferrites on my coax near the antenna and near the radio with no change.It appears that the cab is "charged" with RFI. When we use a quarter wave mag mount and move about a foot away from the cab the RFI disappears. As we move to the bed rail the RFI also goes away.

Are those ferrites rated for VHF, or are they HF ferrites? For example, the thin rectangular snap-together ferrites from Radio Shack (#273-104) are for 3-30 mhz. The snap-on-cable types with a hole in the middle are very good at VHF, 30-300 mhz. (RS # 273-105). I'd probably start with 4 of them if they fit your cable.

[ResQguy]

Originally Posted by cknizeski

There is different thoughts on that. I was always told it is better to go directly to the Battery with the ground, but to be sure to fuse the negitive to prevent it from becoming a return path back to your radio.

This is from K0BG's web site an extremely informative site on all aspects of a mobile install including noise elimination Wiring & Grounding

KØBG.COM

"Although there are two schools of thought with respect to where the power cable ground of an amateur transceiver should be connected, all agree that the chassis should not be used as a ground return. While this practice was wide-spread in the past, doing so in a modern vehicle should be avoided at all costs. It is important to remember that today's vehicles are rolling computers, with some models having as many as 50! Each one of these CPUs has sensors connected to it which control every facet of operation. Using the chassis for a ground return can cause a ground loop to occur which can corrupt the data read from them".

Interesting that every new police vehicle manufacturer is "doing it wrong" by providing a chassis ground stud in the trunk... I think we will continue to follow their guidelines to maintain warranty compliance. It's been my experience that every vehicle owner's manual provides at least some guidance in installing electrical accessories (though most of them lean towards airbag safety or non-interference with ABS). I can agree though, that IF you chose to ground to the battery, you must fuse it the same as the positive.

[ozzie]

I totally disconnected the ground to the battery and attached the ground to another battery outside the vehicle and no change in RFI. I then found that with only the power hooked up I am still generating a ground someplace because the radio still powers on. I assume the ground is coming from the coax. I am going to disconnect the red power from the battery and connect it to another battery outside the vehicle tomorrow and see if that changes anything.

[benbenrf]

Ozzie

To the point on this one – if you want the low down in due course will be happy to explain and put all the reasoning & theory into context for you, with pleasure.

From what you have said i.e. your descriptions of the problem, the actual audible sound, and how you have approached it, is revealing.
You have a magnetic interference problem – as opposed to an electrical interference problem. Secondly, it’s also my humble opinion (and my radio/receiver experience is minimal, but I have 30 plus years experience in the defense & satellite antenna business) that the antenna is also not the problem – it is (suprizingly) a power supply problem - which in the case of vehicle means: battery (unless of course you have something like an AC/DC inverter or DC/DC converter in the power supply chain).

Solution: invest in a good quality low pass filter capable of dealing with EMI (the magnetic field component is important here more so than the electrical field component). Must of course be capable of handling whatever amperage is going to run through it. A "coilws" product will do the job (www.coilsws.com). Something like their EMI-P30A or 50A – not cheap, but I am confident once installed that will be the end of the problem. These specific units are reccomended by Rohde & Schwarz, Racal, General Dynamics use them, Agilent as well. They also have some PL type low pass filters (as opposed to the above which are Pi types) but the PL's are about twice the price and I doubt harmoics are an issue here (they seldom are unless youhave loads of electronic gear on the vehicle - just get rid of the fundamentals above 1Mhz or whatever and you'll be fine.

Also - don;t hesitate to phone wscoil - the tech guys (not the sales guys) can be real helpful and know their subject well

Installation note: as a rule Pi type low pass filters are installed & located as close to the battery as possible, but I have used them right up against the DC power connections on instruments like signal analyzers/receivers in direction finding vans with equal and better results on occassion.

If you do decide to invest in a P30A or similar, great if you feed your results back to the forum. Power supply filtering is an issue that catches a lot of folk out when installing scanners/receivers into vehicles.

[ozzie]

benbenrf--I can tell that you are surely a thinking man. This looks very promising. I will give them a call and order what I need.

[ozzie]

I believe that after alot of looking online that the cause of my RFI is the coil packs on this truck. I found another thread of a 2010 ram truck with the same issue. Would bonding be of any help? I have seen articles on ham radio sites regarding this. I have already tried to install ferrites on the coil pack wires without any luck. I maybe am not using the correct material in the ferrites or not using enough ferrites, or possibly have them in the wrong place. If I were to try and put them on the coax would I put them near the antenna or near the radio? What material number would work best for VHF high band??

[ozzie]

I have since found this info on the subject. http://www.batboard.batlabs.com/view...hp?f=8&t=72881

[jfhtm350]

http://www.batboard.batlabs.com/view...hp?f=8&t=72881

The requested URL was not found on this server.

[W2NJS]

Why do all of you helpful people continue to ignore the possibiliity that the cause of the problem is the electric fuel pump?

[ozzie]

[I] took it to the dealer today and they disconnected the fuel pump while it was running and when I was recieving the interference and it did not alter the interference at all.

[benbenrf]

Originally Posted by ozzie

I believe that after alot of looking online that the cause of my RFI is the coil packs on this truck. I found another thread of a 2010 ram truck with the same issue. Would bonding be of any help? I have seen articles on ham radio sites regarding this. I have already tried to install ferrites on the coil pack wires without any luck. I maybe am not using the correct material in the ferrites or not using enough ferrites, or possibly have them in the wrong place. If I were to try and put them on the coax would I put them near the antenna or near the radio? What material number would work best for VHF high band??

Ozzie

Unless you use the correct ferrite type in the correct way and positioned correctly, there use becomes hit and miss.

Criteria that need to be addressed to do this properly are:

- what is the frequency of the interference
- what amount of attenuation is required at this frequency

Some figures for the above are going to determine the ferrite size required i.e. inner/outer diameter differences (ratio), and the material the ferrite is made out of (which determines it’s permeability).

When you have all this info you can calculate amongst other things, for example the amount of times you need to loop the cable through the ferrite core. This is quite important because the loops made through the core determine the frequency & bandwidth at which max interference attenuation will take place.

In short, to get ferrites to attenuate interference is not simply a case of looping a cable through a ferrite of x diameter – you need to have some understanding of the characteristics of the interference, at least it’s frequency, it’s strength and it’s bandwidth…….. otherwise I suspect your time & effort will come to zero. Some knowledge of the impendence of the circuit it is going to be used in would also help.

There are loads of online resources on the net that can be accessed via Google which will show you how to work this all out. It sounds complicated, it’s actually quite straightforward.

Good Luck

[techman210]

You can mess around with ferrites all day long, but professional installers put in a brute-force filter, FIRST and then break out the ferrites as a last resort. The OP has already been recommended a good filter, and this page has some that I have had good luck with in the past:

DC Power Onboard with Newmar offer Copper Strap, Copper Screen, Ground Shoes, and Noise Filters. Grounding Straps are an ideal conductor for RF grounding of SSB radios and other noise sensitive transceivers or bonding of thru-hulls. Ground Shoes prov

Lots of things can affect RFI that leave you scratching your head. I saw off-brand spark plugs create interference at 460 MHz and not 155 MHz.

Two exact similar diesel trucks, had two different high-end Motorola radios installed, both had the same level of AC hash from the electrical system when we put an o-scope on it - only one radio had a problem.

You can run in circles all day long, but after verifying good grounding on all points (including at the antenna mount) slap in a filter and see what happens. Then get creative. Time is money.

[ozzie]

I am finally getting more info from the service manager at the dealership in Little Chicago,WI in 5 minutes than I did in the last 6 months. The service manager went through his channels at Chrysler and they said they have filters for the issue. They just needed to know the band I was operating on. The service manager said the RFI is surely coming from the coil packs. Many of the vehicles they sell already have 2 capacitors on the engine, but the trucks do not. The engineers at Chrysler will determine the correct filter,placement and method and get back to the Service manager. I went to 3 other dealers and they all knew nothing or blamed the installer for the problem.

[trsundstrom]

Wirelessly posted (Moto Droid Bionic: Mozilla/5.0 (Linux; U; Android 4.0.4; en-us; DROID BIONIC Build/6.7.2-223_DBN_M4-23) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30)

I would have the dealer, if not you, bug the appropriate engineering departments in Detroit. You can't be the only owner with such a problem. A few eons ago I got helo from Ford. HTH.

[Matthewy8]

I'd be interested in what you found. I have a dodge magnum with the same engine and same exact problem. I've bonded the hood grounded the exhaust in multiple places. tried the ferrite beads on the ignition coils and injectors replaced the ignition harness capacitor (it was leaking anyway). Still no fix.

[ozzie]

Matthewy8, I have now grounded the PCM to both the block and the body and added a total of 4 mopar capacitors to the coil power wires and no luck at all. I am aware of the same vehicle being used at a park reserve for law enforcement and spoke with one of the guys there. He has the same problem and has also had no luck. When I took it to the dealer this week one of the engineers at Chrysler actually called the tech back on the phone. They had a discussion, but no fix yet.