UHF CH5 Engine Interferrence on GME4200

Submitted: Saturday, Apr 01, 2006 at 13:08
ThreadID: 32420 Views:1659 Replies:9 FollowUps:8
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Hi Guys, and the Gals.

I am picking up engine interferrnce through my GME 4200 UHF CB on Ch5.

It's picking up the revs of the engine and when i accelerate, this is emulated through the GME speaker.
This causes hassle as i can't scan - the bloody thing keeps locking onto the engine!

I was told to go and buy a EMI block thingy.

As the car i have is a Mitsubishi magna '95 V6 3.0ltr, do i need to buy 6 'EMI thingys' one on each plug lead, or do i need one EMI thingy for somewhere else, or attach it to the GME somewhere?

I'm using a RF Ind 6db anntenna.

Is there any specification that i need when buying a EMI thingy - they look just like a ferrite core thing - for different cable thickness's upto 10mm.

Any help would be appreciated.

Thanks,
Alan.

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Reply By: Member - Troll 81 (QLD) - Saturday, Apr 01, 2006 at 14:22

Saturday, Apr 01, 2006 at 14:22
Alan

I dont know what a EMI thingy is but why cant you just skip scanning that channel?

AnswerID: 164250

Follow Up By: Mad Dog (Australia) - Sunday, Apr 02, 2006 at 07:07

Sunday, Apr 02, 2006 at 07:07
Not a good idea to block the emergency channel.
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FollowupID: 419210

Reply By: PandJ - Saturday, Apr 01, 2006 at 14:35

Saturday, Apr 01, 2006 at 14:35
G'day Alan,

What the hell is EMI block thingy? maybe they mean a "thingamagig"!

If I were you i would take it to the place of purchase, let them hear the noise and see if they can get onto GME Electrophone as it could be in the transmitter. If no good seek out a good Auto Electrician.
Good luck P@J
AnswerID: 164255

Reply By: arthurking83 - Saturday, Apr 01, 2006 at 14:44

Saturday, Apr 01, 2006 at 14:44
I don't think you need a specific type ????

I'm not a radio guru, but I've had the same trouble you had, and I fixed it by re-routing the antenna cable (the coax).,

I've had similar troubles with AM band on the car radio, and found that the EMI 'slugs' didn't help!

I have a number of electronics devices...cameras, etc... and some have EMI cores fitted to the cables(from the manufacturer), where the cable passes through the core and then wound around to come back through the core again!

Don't know if that's the way it supposed to be done????

AnswerID: 164256

Reply By: Kiwi Kia - Saturday, Apr 01, 2006 at 16:09

Saturday, Apr 01, 2006 at 16:09
EMI thingy = Could be a resistor type suppressor for fitting in line with spark plug leads, not required these days with suppressor ignition leads.

Could also be small suppressor chokes or capacitors fitted to generator or alternator leads.
AnswerID: 164271

Reply By: Darian (SA) - Saturday, Apr 01, 2006 at 16:25

Saturday, Apr 01, 2006 at 16:25
Might be easier as mentioned above to delete that channel from your scan sequence. You can still use the channel manually for repeater work, when required. Had to do that on Ch 35 with my Icom 400 Pro - the Barrett HF 950 puts out some rubbish on that frequency - my handheld UHF won't scan past that channel either within 10m of the Barrett. Radios ! Just as well we enjoy such toys.

AnswerID: 164274

Reply By: Member - Mike DID - Saturday, Apr 01, 2006 at 16:26

Saturday, Apr 01, 2006 at 16:26
If the interference is ONLY on Channel 5 then interference suppressors will not help. This would be due to radiation from the clocks in one of the computers in the car. Could be Engine Management system or anything.

Mike
AnswerID: 164275

Follow Up By: Alan Southport QLD - Sunday, Apr 02, 2006 at 06:53

Sunday, Apr 02, 2006 at 06:53
Hi Mike,

I wouldn't have said that my computer management system (clocks), was going - yet :)

Ch5 is 476.525Mhz. So the interference is around that range.

I'm not dismissing your reply, but for now, i'll look at other solutions first.

Thanks,

Alan.
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FollowupID: 419209

Follow Up By: Member - Mike DID - Sunday, Apr 02, 2006 at 07:12

Sunday, Apr 02, 2006 at 07:12
Do you get interference on Ch4 and Ch6 ?

Does the interference start when you switch on the Ignition or after you start the engine ?

Mike
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FollowupID: 419211

Follow Up By: Alan Southport QLD - Sunday, Apr 02, 2006 at 07:31

Sunday, Apr 02, 2006 at 07:31
Hi Mike,

Had to go to the car and check :)

Ch4 and Ch6 are clear (well Ch4 is dead clear), and if i was paranoid extremely little is coming through on Ch6, but hard to tell really. Only that the engine noise is REALLY clear on Ch5.

With the squelch set fine Ch4 and Ch6 stayed quite - but Ch5 cuts in.

With the ingnition on and ACC, nothing came through. Only when the engine is running.
Jerry replied thinking that it might be the alternator, but he has mentioned to check the leads - but i'm not sure how to.

I'm hoping that what i have tested for you, it is not the ECU :(
What do you think?

Cheers,
Alan.

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FollowupID: 419215

Follow Up By: Member - Mike DID - Sunday, Apr 02, 2006 at 08:53

Sunday, Apr 02, 2006 at 08:53
Ignition interference gets in via the aerial - disconnect the aerial to verify this.

Alternator whine comes in via the power leads - run the radio off a battery to verify this.

I have NEVER come across Ignition Interference or Alternator one that affects one channel, but not the one next to it. It has to be a crystal-controlled frequency - hence assumimg it is a computer-generated signal.

Or does it only happen with the vehicle parked in one location ?

Mike
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FollowupID: 419226

Follow Up By: Alan Southport QLD - Sunday, Apr 02, 2006 at 15:14

Sunday, Apr 02, 2006 at 15:14
Hi Mike,

Just got back in....

I haven't been able to run it off a stand alone battery, yet. Another day for that.

I disconnected the aerial from the back of the GME unit (as it sits on it's side near the passenger well), and found something interesting.

When the centre core was touching - the interferrence was really nice and clear - very little static - lots of very quick ticks etc or sharp broken static.
Connecting the aerial fully allowed the Interferrecne and static noise to come back through.

I thought i just needed a EMI thingy and ask you guys, the experts before i had to take it to an auto electrician.
As i haven't had a reply from Jerry yet, do you know where to test the Ohms on the spark plug leads?

Cheers,
Alan.
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FollowupID: 419264

Reply By: Member - Jerry C (WA) - Saturday, Apr 01, 2006 at 22:01

Saturday, Apr 01, 2006 at 22:01
Hi Alan,
You say that the noise varies with the speed of the engine, so I would suggest that it comes from the alternator which is is more of a high pitched buzzing noise or from the spark plug leads, the plugs are more of a tick tick tick. EMI is "Electro Magnetic Interference". So maybe the brushes in the alternator have passed their use by date or the plug leads are starting to go open circuit and are sparking across the faults. If you have a meter which will measure "Ohms" good plug leads will measure 10,000 to 15000 ohms depending on their length.

Good luck

Jerry.
AnswerID: 164322

Follow Up By: Alan Southport QLD - Sunday, Apr 02, 2006 at 06:50

Sunday, Apr 02, 2006 at 06:50
Thank you Jerry,

I didn't want to block the channel out (which of course would have been the cowards way out), as i do sometimes get locals on it.

You were the only one who actually answered my question - How do i stop this noise?

I think you are correct in that it is the alternator brushes.

But staying with the ticks - i do have a DMM. Where would i place the probes to measure this resistance - and should the engine be running?

Thanks.
Alan.
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FollowupID: 419208

Follow Up By: Mad Dog (Australia) - Sunday, Apr 02, 2006 at 07:40

Sunday, Apr 02, 2006 at 07:40
Alan, you are right not to block out channel five as it is the emergency channel and should be monitored for emergency calls.
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FollowupID: 419216

Reply By: Member - Jerry C (WA) - Sunday, Apr 16, 2006 at 22:43

Sunday, Apr 16, 2006 at 22:43
Hi Alan,
Sorry about the delay in answering.
To measure the resistance of the plug leads you do it with the engine off. You need to measure between the the ends of the leads, this may require the removal of the distributor cap so that you can access the six terminals inside. I don't know how practical it is to do this on a Magna so it maybe better or a lot simpler to talk to your friendly auto electrician.

Cheers, Jerry
AnswerID: 167302

Reply By: geordie4x4 - Sunday, Apr 16, 2006 at 23:11

Sunday, Apr 16, 2006 at 23:11
Alan,
I have been having the same problems with my Uniden UH012 and also had alternator problems. The alternator has been fixed and the radio problem has gone. The alternator usually has a small interference suppressor on the outside that you might ckeck first to see that it is properly earthed.

As for the EMI thingy it is simply a magnet.
AnswerID: 167310

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