Interference on FM radio

[Tony x]

Hello all,
I'v trawled the web for an answer to this question but I'm still unsure which way to go.
Since fitting a dash cam, I'm getting a whole load of crackling through the FM radio. If I disconnect the power supply to the cam, it goes away.

I'm not sure if I should fit a noise supressor to the radios power supply like this perhaps? http://www.amazon.co.uk/RADIO-STEREO-12 ... terference and, if so, do I need 2? - one for the main supply and one for the 'always on' supply.

I've also read that if you set up the radio so it has its own dedicated power supply cable from the battery,this sorts out such issues.

A third alternative (so I've read) is to put a choke around the power lead to the dash cam. However, I'd sooner sort things at the radio end if possible so that any further gadgets don't mess it up.

I've never installed a radio in a vehicle and it's all a bit new to me as to how to solve such problems.
Advice much appeciated.

[g8dhe]

You use the term "crackling" which doesn't quite tally with the normal types of radio interference, if you had said there was a "burble" or "hissing noise" it would be different. "Crackling" would normally be associated with a bad connection, where do you have the Camera plugged in ? I'm guessing the standard cigarette socket, which is in fact the same feed as the radio power, so my first step would be to check the reliability of the socket and the plug on the camera.

[Tony x]

Cheers for the reply g8dhe
The connections are sound - the camera is hard wired in and other devices on the same circuit work fine and didn't cause an issue with the radio.
Likewise the plug for the camera is also fine.
By crackling, I mean the sort of sound you might hear in pre Freeview TV days when your telly was not properly tuned into a station
Any thoughts?

[silage]

Could be EMC from the camera if the device is close to the antenna cable? You might need some sort of chock on the cable, try calling in to some one who fits radios and let them have a listen?

[Tony x]

Cheers silage,
Would that be a choke on the cameras cable or the radios?

[g8dhe]

By crackling, I mean the sort of sound you might hear in pre Freeview TV days when your telly was not properly tuned into a station
Any thoughts?

It sounds like the cameras power supply is generating noise in that case.
If you can lay your hands on a ferrite core the type you see on Mains leads and good quality USB leads, then you could wind a couple of turns of the power lead to the camera around it as close to the camera as possible see here for a suitable type http://cpc.farnell.com/ke-kitagawa/grfc ... dp/FT01639
or a range of them http://cpc.farnell.com/webapp/wcs/store ... sults=true you want to be able to pass the cable at least twice or even more if possible.

[g8dhe]

Just a thought your not using a window screen aerial are you ?

[Tony x]

Thanks again g8dhe.
No, it'sthe standard Bongo aerial.
I'll give the ferrite core idea a go.
I might just try connecting the radio directly to the battery to see if that helps also and, with a losely held in radio, it should be a quick test.

[Diplomat]

It is very unlikely to be the radio's 'fault' if the radio and the earthy side of the aerial are properly bonded to the car's metalwork and if the normal reception is fault free.

If there is an actual power supply unit for the camera, it could be the culprit, in which case a choke in the lead placed near the supply unit might reduce the noise. the However, the noise source could also be the camera itself.

If the camera is fed directly with 12 volts via a lead with no gizmo at the vehicle end, then a choke in the lead adjacent to the camera might cure it, but only if the interference is radiating from the lead. If it is radiating through the plastic camera box, then the camera may need screening, with the screen bonded to car metalwork.

Check the integrity of the ground connection of the coaxial aerial cable at the aerial fitting. If it is not good, all manner of unwanted signals will be picked up by the cable as well as the metal antenna itself.

Try moving the position of the dash camera, relative to the radio, the aerial,and the aerial lead to the radio. If nothing cures the problem, you may need to consider mounting a different aerial near the rear of the van.

EMC stands for electromagnetic compatibility and all devices should be constructed to meet the fairly strict EMC rules. In order to meet the specifications, many manufacturers will produce a design which passes the test but when it comes to the production run, leave out the necessary suppression components. The empty spaces on the board and unused solder pads give the game away. This practice doesn't stop the device working but saves a lot of money across a huge production run. Unfortunately, the practice is widespread and will only be stopped if authorities can seize items which have had the components left out. This doesn't usually go down well with innocent purchasers who are not receiving interference themselves. Such is the wonderful commercial world we live in.


Frank

[Simon Jones]

I've got a dashcam in both vehicles and they tend use a standard 12v to 5v USB power adapter. I bought a few of these made by Belkin which actually whistle when under load and you can even hear them with the engine running (those V6's are so damn quiet ). It's the switched mode power supply inside that runs at a high frequency that makes the whistle an will likely be transmitting interference too.

Try replacing it with an alternative one. I've bought a couple from Poundland which are 500mA so plenty powerful enough and you can also get the matching USB lead there if you need one too.

[Dodgey]

I had the same problem with a cheap dash can. It was the 12v power adapter. Cheap Chinese unfiltered power supplies. Bin it and us another .

[Tony x]

Lots of useful info' given...thanks.
I've got a few more tests to do to determine what might be the cause of the issue including trying a different psu (which is 5v) trying the camera powered by a portable psu so it's completely free from the vehicles electrics and plugging a sat nav into the end of the lead the camera goes.
I'll post when I get to the bottom of it . I'm hoping I don't have to shield the camera.

[Tony x]

All's sorted and the radio is fine now. It turned out the radios chassis wasn't earthed. Now the sound is better than its ever been,
Cheers for all the input,
Tony