Noise filter for mobile - Elmers Forum at eHam.net

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Noise filter for mobile	Reply
by KI4LIV on October 30, 2005	Mail this to a friend!
Greetings, I recently upgraded from an FT-7800R to a TM-V708A. Both radios suffered from a condition of where if I have a signal that is somewhat weak but readable, I am getting engine noise from my 2004 Chrysler Sebring. When I am somewhat close to the repeater or transmitter, the problem is not there - only with the distant stations. Both radios connected directly to the battery. This is happening both on simplex and duplex. I've read about noise filters for a long time but looking back at my "chicken band" days, I never found one that worked. Of course, the same filters may actually work on FM, but on AM they didn't do squat. So, my question is : Will a "noise filter" actually help this problem? Any one in particular that comes recammended? Thanks in advance! KI4LIV

RE: Noise filter for mobile	Reply
by K6AER on October 30, 2005	Mail this to a friend!
I sounds like the noise is coming in via the antenna line. By getting closer to the repeater the signal strength is capturing the interference. There might not be much you can do about radiate noise from the vehicle electrical system but here are a few suggestions. With a AM radio or a HT you need to find out if the noise is from the alternator, ignition, microprocessors or other electrical sources. Good grounding of the antenna mount area sometimes will help. From you description your noise does not sound like it is coming in via the DC line. Try to find a local Elmer who has mobile installation experience to help you. Also noise filters are for DC conducted noise and will not help noise from the antenna.

RE: Noise filter for mobile	Reply
by K7AAT on October 30, 2005	Mail this to a friend!
You did not specify if the noise is coming in on the antenna, or by way of the DC power lines. If on the power lines, (AKA alternator whine, or whatever), there are DC filters which you can buy and install in the power line. If coming in on the antenna, then something in your vehicle is generating an interfering signal. Depending on your antenna setup, you might be able to relocate the antenna to attenuate the interference. Better would be to find the source of the signal. Does it come on with the ignition turned off? Pulling various fuses (one at a time), while hearing the interferance is a good way to isolate where it is coming from. Once you hear the interferance go away when a certain fuse is pulled you can refer to the particular circuit it is on to pin point the interference and then deal with it. Good luck. Ed K7AAT

RE: Noise filter for mobile	Reply
by KI4LIV on October 30, 2005	Mail this to a friend!
The noise is a buzzing sound when idle, and when in motion the buzzing sound alternates speed along with the engine. No whine. I am using a Larsen trunk lip with an antennex nmo mount antenna. I have removed the antenna from the trunk completely to see if that would help (with engine idling), but no change was seen. I don't know if this will help, but the same sound can be heard on my IC-W32A HT when running it in the car off of the stock duckie antenna and running off it's own battery. KI4LIV

RE: Noise filter for mobile	Reply
by N6AJR on October 30, 2005	Mail this to a friend!
I ended up puting ferrite beads on my spark plug wires and the wires leading up to the coils ( the new type where each plug has a coil), also ground the neg side of the battery to the chassis, and ground the tail pipe to the chassis and put ferrite beads on the electric fuel pump, good place to start

RE: Noise filter for mobile	Reply
by K7AAT on October 31, 2005	Mail this to a friend!
"The noise is a buzzing sound when idle, and when in motion the buzzing sound alternates speed along with the engine. No whine." I'll assume that the noise goes away with the engine off? This sounds like ignition noise to me. There is a good sized catagory of procedures to deal with ignitioin noise. The ARRL handbook should give you a good start. If your vehicle does not already have them, I'd suggest you get a set of "resistor" ignition wires to replace the stock spark plug cables. Ed K7AAT

RE: Noise filter for mobile	Reply
by K0BG on October 31, 2005	Mail this to a friend!
If you're getting enough ignition noise to be heard when the radio is in the FM mode, you're going to have to do more than install a noise filter or a couple of beads. Incidentally, I have known of just two cases where ferrite beads installed on the high tension leads reduced radiated RF from the ignition system. The ignition noise when the radio is in AM mode is very common, and I'd be surprised if you didn't have a lot of it considering the make and model, especially if it has over 25K miles on the plugs. The first thing I would check is the continuity of the coax. The shield could be open on the antenna end and you might not notice it even with an SWR bridge. If you want to make sure it is ignition (and it probably is), go to my web site and look under Noise ID. Alan, KØBG www.k0bg.com

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