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Author Topic: intermittent interference in jeep  (Read 641 times)
KC6TJK
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Posts: 4




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« on: February 16, 2002, 01:08:03 AM »

I have been having a problem with intermittent interference in my 1997 jeep cherokee. I have had this problem since I got the jeep about 7 months ago. It happens with the ignition on but vehicle not running, and with the vehicle running. It will be fine for a few days then start again. If I disconnect the antenna it will stop. Sometimes it will start and I will have this problem for about an hour and then it will stop. I have this interference in both my 2m/440 Kenwood G707 and a Motorola vhf radio but only on 2m 440 is fine. Any ideas?
Thanks
Bob
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WPQX931
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« Reply #1 on: February 19, 2002, 01:25:38 PM »

Assuming you are getting intereference from RF.  and your electrical system is properely installed.

There are plenty of things in your jeep that can cause rfi.  anwhere from ignition, injectors, fuel pump, air pump, fans, fans and blower,  ECU, alternator, one of many other electronic modules that controls various convinence features. you can determine that by observing how the noise sounds like.  varies with engine speed, varies with road speed, or constant at all time.

first, where is your antenna located?  what kind of mounting and cable are you running from the antenna to the radio.   usually the top of the roof is a good spot because it is the furest away from anything that makes noise and a nice shielding(roof) protects it from intererference.  use a mag mount on your roof and see if it makes any difference.

After that make sure your cable connections are tight and properely installed.  a bad connector or a coax that is stripped too much can pick up all kinds of stuff.

I would first get a bat
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WPQX931
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« Reply #2 on: February 19, 2002, 01:29:03 PM »

sorry,

I just reread your post...

key on engine off..... that eliminate the fan, injector, coil, fuel pump,

that leave ECU, electronic modules, mainly ECU. but still  check the anteanna system

Alex
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KB9YNB
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« Reply #3 on: February 25, 2002, 10:34:36 PM »

Actually,
most cars today WILL run the fuel pump for a little bit with the key on but the engine off.  it shouldn't run continuously with the engine off, however.  I'm not familliar with the Cherokee, does it have an electric engine cooling fan?  These will definitely run with the engine off and could be a significant source of RFI.  Does your cherokee have a power antenna for the broadcast radio?  is the motor on THAT causing your interference?

Just a few ideas!  

73, KB9YNB
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KC6TJK
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« Reply #4 on: February 26, 2002, 01:32:15 PM »

I don't think it's the fuel pump because the last time I was testing to fix my problem I had the key on for a good 10 min. As far as the electric fan goes, yes it has one but it only runs when the temp is up at about 200 degs. There is no power antenna for the am/fm. I have tried a mag mount and moved it all over the top with no change. It is very strange I will have no problem for days then it will have interference for 5 min up to an hour then it will go away. Would double shield coax help? I have one 3/4 roof mount on now and can change out the mount and coax to this if it will help.

Thanks for the help
Bob
kc6tjk
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