Radio interference when rev motor with ipod

Submitted: Thursday, Mar 09, 2006 at 21:48
ThreadID: 31596 Views:2137 Replies:7 FollowUps:10
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Not really a 4wd question as such - but there I reckon it should be ok as I use it alot when camping :) Anyway I had a quick search and nothing exact. I hope someone can help.

I have 3l td Patrol GU. Also have Ipod video using an FM transmitter. When this is on, I am getting interference coming through stereo from the car motor. Does not exist when just playing stereo normally. As I rev the motor, you can hear the interference pick up with it.

Any suggestions as to where I start to eliminate this interference?



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Reply By: crfan - Thursday, Mar 09, 2006 at 21:57

Thursday, Mar 09, 2006 at 21:57
Hi Alan,
Do you have the FM transmitter running off its Batteries or 12v supply .Mine doesnt do it off its own batts but does if its plugged into the cig lighter and if i move the cords around can change it but not stop it.
AnswerID: 159597

Follow Up By: Member - Alan (WA) - Thursday, Mar 09, 2006 at 22:46

Thursday, Mar 09, 2006 at 22:46
Running from 12v not batteries - I will try battery power and see if it makes any difference. Would be a shame if this were the case as I try not to have things that require too many batteries.

FollowupID: 414242

Reply By: Lone Wolf - Thursday, Mar 09, 2006 at 21:58

Thursday, Mar 09, 2006 at 21:58
Two things...

1) Signal Strength. Is your iPod in a position whereby the signal strength is being impeded, making the transition to your antenna a hard task?

2) Frequency. Have you used all the available bandwidth on your FM transmitter?

After trying those two things, then maybe an Auto Electrician could have a quick look for you.

AnswerID: 159598

Follow Up By: Member - Alan (WA) - Thursday, Mar 09, 2006 at 22:49

Thursday, Mar 09, 2006 at 22:49
Yep should be no impediments to signal.

Am trying different frequencies - so far no real change.


FollowupID: 414243

Reply By: Sand Man (SA) - Thursday, Mar 09, 2006 at 22:00

Thursday, Mar 09, 2006 at 22:00

iPod Video???

Most FM transmitters have alternate channels to select. Have you tried different channels in search of a channel with no interference?

Alternatively, you could try replacing the FM transmitter within an adaptor that interfaces between the iPod and the tape slot of your car sound system, assuming it has one. This will eliminate any possibility of the transmitter being the cause.

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AnswerID: 159599

Follow Up By: Member - Alan (WA) - Thursday, Mar 09, 2006 at 22:51

Thursday, Mar 09, 2006 at 22:51
Has a tape drive - so I guess I could get a different connection.

I read a previous post about someone hooking their ipod up to their stereo via the CD changer option - hard-wired. Like this idea and someone said can get wiring via West Coast Hifi - will look into this alternative.


FollowupID: 414244

Reply By: Eric Experience. - Thursday, Mar 09, 2006 at 22:03

Thursday, Mar 09, 2006 at 22:03
I asume you have the fm transmitter in the vehicle and you are using the radio antenna on the outside of the vehicle, if the fm transmitter is connected directly to the radio antenna plug you will be ok. Eric.
AnswerID: 159600

Follow Up By: Member - Alan (WA) - Thursday, Mar 09, 2006 at 22:54

Thursday, Mar 09, 2006 at 22:54

Connecting direct - like to sound of that - I would love to say I know how to do that.....but alass.....not.

Hey but I am not proud - How do I do this?

FollowupID: 414245

Follow Up By: V8 Troopie - Friday, Mar 10, 2006 at 01:43

Friday, Mar 10, 2006 at 01:43
Alan, I do not think its possible to do what Eric suggests. The 4 frequency Belkin FM gadget I have has its antenna within the short (15cm) wire that goes to the headphone socket. I doubt that any of the other ipod FM transmitters have an accessible antenna connection.

What I do on my boat is to run the ipod from the belkin/ ipod cig socket accessory. This has a headphone skt where I plug in the FM transmitter.
I had some interference but velcroing the FM transmitter in a certain place fixed it. Of course, I had some choice where to place the cig lighter skt as well.
In my troopie I feed the Ipod headphone output straight into the CD input of the cassette only stereo. Perfect sound. I did try first the FM transmitter option but had problems like you, maybe fitting another cig socket elsewhere and with ferrite suppressors might have cured it.

Another thing to consider, if the FM transmitter uses AAA batteries (mine does) is their life span. I'm convinced the gadget runs these batteries down reasonably fast and a low battery is equal to a weak FM signal.
I fixed that one with a small regulator set to 3V output @ 12V input, no more battery problems. Connection was simply via dummy ( dowels & thumb tack) "batteries".
FollowupID: 414264

Follow Up By: Member - Alan (WA) - Friday, Mar 10, 2006 at 10:25

Friday, Mar 10, 2006 at 10:25
Hi Klaus

My setup sounds similar to what you mention -. Runs off 12 v -The FM trsnsmitter I use is digital and can use a wide range of settings..
FollowupID: 414292

Follow Up By: Eric Experience. - Friday, Mar 10, 2006 at 22:07

Friday, Mar 10, 2006 at 22:07
To test the theory place the ipod close to the antenna, if the noise stops you can go ahead and improve the connection. If the noise does not stop then you will have to place a filter in your supply to the ipod. to make a direct connection to the radio you can remove the radio and plug in to the antenna plug a cable with a switch to connect to the ipod or the original antenna, if there is no antenna terminal on the ipod all you have to do is tape a wire close to the built in one. Eric.
FollowupID: 414463

Reply By: Mike DiD - Friday, Mar 10, 2006 at 07:20

Friday, Mar 10, 2006 at 07:20
There are two types of these FM transmitters. Those that have fewer than 8 frequencies use a simple method for controlling their FM Transmit frequency. This means the frequency drifts, so there is a very good chance they will be transmitting off the correct frequency.

This makes them very prone to any interfernce.

Summary - if you are buying an FM transmitter, make sure it has at least 8 transmit channels.
- if you have one with less than 8 channels and you get interference - there's not much you can do.

AnswerID: 159644

Follow Up By: V8troopie - Friday, Mar 10, 2006 at 12:45

Friday, Mar 10, 2006 at 12:45
Thanks Mike, good advice, I wasn't aware of that. I was thinking of getting a better FM gadget at some stage for my boat, preferably one that is also powered from the Ipod to reduce the wiring complexity.
FollowupID: 414327

Reply By: Blackcat - Friday, Mar 10, 2006 at 09:17

Friday, Mar 10, 2006 at 09:17
Hi Alan, It is many a year since I worked on engine electrics however, if my memory serves me correctly, and it sometimes does; your problem may stem from your alternator. The faster the revs the more interference and the slower the revs the less? If this is so you may try going along to your auto electrician and ask them for a suppression capacitor. From memory around the 0.1 microfarad electrolytic should do the trick. You would need ask their advice as to where it should be fitted as there may be a number of alternative places to fit it. Good Luck Blackcat
AnswerID: 159658

Follow Up By: Member - Alan (WA) - Friday, Mar 10, 2006 at 10:28

Friday, Mar 10, 2006 at 10:28
Yep - high pitching sound - goes up up with the revs. I will try moving it around a bit first and make sure I have everything set ok. If not, I will do as you suggest. It's a bit of a needle in a haystack if you don't know what to look for.Thanks alot for the advice Blackcat.
FollowupID: 414294

Follow Up By: Mike DiD - Friday, Mar 10, 2006 at 13:12

Friday, Mar 10, 2006 at 13:12
ok, this combined with "Running from 12v not batteries " makes it clear that the AC from the Alternator on the 12 volts is causing the problem - an Alternator puts out rectified AC - not DC.

What you need is something that can filter out audio frequencies in the 12 volt feed to the Ipod - if it had been designed to work off a car supply you wouldn't have this problem. If you go to an Auto electrician describe it as Alternator Whine.

A 0.1 capacitor will only with radio frequency interference getting into the radio aerial.

I don't know of one that has Cigarette Lighter Plug and socket ready made. You could wire this one into the Cig Lighter socket for loads up to 5 amps - just don't use the Cig Lighter on it (it draws 10 amps)

FollowupID: 414336

Reply By: Lorne - Friday, Mar 10, 2006 at 18:26

Friday, Mar 10, 2006 at 18:26
go to and search for this CAT. NO. QM3780 this could be another alternative for your problem. It connects inline with your antenna and should cut out the interference
AnswerID: 159759

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