Electrial Rf interference, theory and practice of using Ferrite Ring Cores 'choke'

[ChrizK]

I appreciate that @mark641 asked how ferrite cores work here, answered by @Lucien Nunes , but TBH, it is at a deeper level than I need.
My question is more so in regard to the practical use of them.

I (unfortunately) bought a Road Angel Halo Pro dashcam ...I bet you can already guess the problem ...my DAB Radio.
Speaking to Road Angel, they say that they are aware of the problem for 'a few' customers. My immediate response was 'but if it is only a few, does that mean that some units are faulty producing interference that others do not?'. They refused to accept this but could not give me a reasonable answer to the question. However, they suggested a Ferrite Core, to which I answered, I already have added one and it makes no difference. They then suggested adding three ... my response being ... "these things are big and I have just spent the weekend hiding the cables in the trim".

Anyway, I ordered 20(!) from Amazon and proceeded to clip three onto the cable, despite it being completely impractical. As I had guessed, it made no difference. I clipped a further two onto the rear camera, still no difference.

This makes me wonder 'how' best to 'apply' these things. I have seen the cable looped around the core, and alternatively fed straight through. Is there a difference/recommended way? Also, where does the interference 'come' from? I heard one comment that the core should be located as close to the 'device' as possible. Is that correct? This interests me ...is it correct that the device (in my case, the dashcam) creates the interference, but it is the cable that becomes an antenna, which 'emits' the radio frequency?
Considering that I have wired in a 'female cigarette' connection to the car fuse board (using a fuse piggyback), is this also a device?
ie is it valid to add (yet more) cores at this end as well? This perhaps goes back to the question 'is there any value adding more and more of these?'.

Sorry for all the questions, but hopefully someone can be kind enough to reply in laymans terms (and apologies if I have ended up in the wrong forum, but it made the most sense to me!)

 

[Lucien Nunes]

The dashcam generates RF internally, some of which escapes along the power cable and radiates from it, or continues along the vehicle wiring and gets into the radio. Connections along the chain such as the lighter socket do not contribute, although if the 'plug' actually contains a voltage regulator to send say 5V to the camera itself, then the regulator might just possibly be the culprit. (What is the plug like and how is its output connected to the camera... USB?). One wants to trap the RF as close to the source as possible. If the source is the camera, as you have fitted ferrites there without any effect, either the radiation is not from the cable (it might be radiating straight off the circuit boards and through the body of the unit) or it is at frequencies at which the ferrites are not effective. Adding more cable turns can increase the attenuation, but if there is none with a single pass through, adding more probably won't make any difference. You might try moving the unit relative to the car body and radio, while listening for the effect. If that makes much more of a difference than moving the cable, then the cable might be a red herring. The same applies to the rear camera and the voltage regulator in the plug, if there is one. BTW did you simultaneously fit a ferrite core to the rear camera connection leaving the front unit, as well as near the rear camera itself?

The reason only some customers are experiencing this probably lies in the different vulnerabilities of their radios. The dashcam might be naughty in radiating too much interference, but equally some radios might be naughty in not being adequately screened against it. Mutual interference has been an ongoing issue with electronics for over a century and a significant fraction of product R&D and cost is associated with controlling it both inbound and outbound. Some pairings of devices are going to be more problematic than others. It might be showing up some deficiency in your aerial or aerial wiring that has otherwise gone unnoticed, i.e. the aerial signal is weak but adequate (with digital, you might not be aware of a problem via the audio) in which case the interference is relatively much stronger.

 

[ChrizK]

Thank you @Lucien Nunes , I hadn't thought about 'the other end' properly. You are absolutely correct to guess it is a USB connection ... I am attempting to use the cable provided with the dashcam, rather than the additional purchase of the Road Angel 'hard-wire kit'. (considering I already have a cable, I not only consider the price of the HWK12 to be expensive, but also note comments saying that it is not correct for the new model ...no idea if true, but thought I would try an alternative).
I will try adding a core at that end too (along with the existing cores at the front and rear cameras).
Your advice and insight is greatly appreciated, although I am not sure if I will try all the investigation suggested ... I may find it is the camera position in relation to the radio, or the radio itself, but that ultimately means I can't use them together, so I end up down a blind alley

...just re-read your question ... could it be beneficial to remove the core at the front camera, leaving the core at the rear (which is as close to the rear camera as possible)? ...sorry, re-read again (and remember how I first understood) ... "leaving the front unit". TBH I can't remember where the cables split. I will have to remove it all as it is all 'nicely' hidden in the trim. Another job for the weekend.

 

[ChrizK]

You might try moving the unit relative to the car body and radio, while listening for the effect. If that makes much more of a difference than moving the cable, then the cable might be a red herring. The same applies to the rear camera and the voltage regulator in the plug, if there is one. BTW did you simultaneously fit a ferrite core to the rear camera connection leaving the front unit, as well as near the rear camera itself?

You were absolutely right to direct me to do more investigation. I pulled all the cabling out and added a ferrite close to the USB socket (inserted into the cigarette lighter as described earlier). The radio came on and I thought BRILLIANT! I then put everything back in place. Later went for a drive and the radio cut out continuously.
The bit of information I didn't provide ... the back camera was dangling from the trim as I didn't want to commit sticking t down with 3M double sided until it was all working. When I thought it was working, I stuck it to the back window. I asked on Ford Owners Club how to hide the cables at the front of the car, and an excellent contributor responded with a detailed answer (although I received this after I neatly installed everything). He told me to be careful of the car aerial and not to attach to the window(!). After investigation, I found that what I thought were heating elements in the back widow, also included the aerials (FM and DAB). So, I had stuck the camera pretty much right on top!!! Anyway, although I had two ferrites attached, after prying off the camera, I found no matter where I placed the camera on the top ledge/surround, the radio cut out ... as the aerial receivers are in very close proximity.
My problems seem to be resolved if I place the camera at the bottom of the window ...but the ledge has an acute angle, so the camera points straight at the sky. Not really sure what to do with that. Guess I need to make some sort of platform
At least I think I know where the issues are, and very much appreciate all the knowledge you have passed on, as it has meant I have some confidence that I have done all I can in the front of the car.
NB I should add, I placed a ferrite where the cable splits to feeding the rear camera. This is actually fairly close to the front camera, but I don't think it made any difference.

 

[Sparkgap]

Have you checked the USB supply? I'm a radio ham and many years ago I found a mysterious signal appearing on 2m and 70cms in my car. Eventually traced it to the plug-in usb in the cigarette lighter in the car feeding my mp3 player, changed it and no more problems. This also cropped up recently with some other usb-using stuff with the same result, I think the interference depends to a great extent on whether the converter is a switched-mode type or a simple voltage divider.

 

[ChrizK]

Have you checked the USB supply?

Thanks for your reply.
I need to build a platform and so the rear camera is still dangling.
The radio mostly works, but it cuts out in areas (irratating) which I am fairly sure is interference from the camera setup.
I may have to venture back to the USB. I guess I should have used the actual cigarette lighter socket before going straight in and wiring in an additional one. Would have been a lot easier to play around to determine the behaviour before concealing everything!

 

[Sparkgap]

Thanks for your reply.
I need to build a platform and so the rear camera is still dangling.
The radio mostly works, but it cuts out in areas (irratating) which I am fairly sure is interference from the camera setup.
I may have to venture back to the USB. I guess I should have used the actual cigarette lighter socket before going straight in and wiring in an additional one. Would have been a lot easier to play around to determine the behaviour before concealing everything!

One thought: if you have one of those power banks with a USB output try connecting that to the camera so it's not physically connected to the car electrics. That would establish if the interference is going through the car wiring from the plug or being radiated and picked up by the wiring.