Dashcam interfering with DAB reception

[PAJ]

Hi ladies and gentlemen
I confess right away to having very limited knowledge in modern electronics (67 years old and remember the Wheatstone Bridge) so please (hopefully) reply in simple terms.

The camera causing difficulty is a Smart Witness Smart-I Duo. I have the main unit fixed to the underside of the plastic cover of the high-level brake light on the rear screen with the secondary camera mounted to the inside cill of the passenger door looking left. (I have a similar arrangement at the front with the camera unit behind the central mirror and the secondary mounted on the cill of the driver's door looking right, so all four directions are covered.)

The car is a 2014 model Skoda Superb Twin Door L & K 170 hp diesel automatic DSG 4x4. This just means that it is the saloon version rather than the estate. It has live television by DAB-t to the Columbus head as well as DAB radio and the interference is so strong that the tv image breaks up then goes off altogether and the radio switches automatically to FM. (Columbus is the name Skoda give to the info-tainment system - the radio/tv/GPS/telephone system displayed on a central screen on the dash.)

There is a shark fin antenna on the roof but this is probably for the GPS and 'phone as placing the camera close to it does not cause any interference with the digital reception. If the camera is brought close to the back window (any closer than the front of the rear headrest) the digital reception seems to be suppressed somehow. I have three of these camera sets and I have tried all three and the same thing happens. I have tried powering them from the car's own always-live sockets (normally the cameras are powered from a separate lighter socket wired from a spare fuse powered via the key, so the cameras come on with the ignition) to no avail and also just from the camera's own battery until it ran out. In every variation, the digital reception was cut off while the camera was on and came back when the camera was off (either un-plugged or after the battery died).

It is as if the camera is emitting some kind of signal that kills the incoming digital signal being received via the heater element in the rear screen or nearby. If I just hold the camera 12-15 inches away from the glass the digital signal returns.

The camera does not have any transmitting circuit (no wifi, bluetoothe or even GPS) but records onto a micro SD card.

It does not seem to be the power input (normal car lighter plug to mini-USB) as the interference stops if I switch the camera off by its own on/off button, and it interference remains if running off the camera's built-in battery.

The only thought I have re the problem solution revolves around a large hammer, so I would appreciate any suggestions from members.

Thank you in advance.

 

[Martaine2005]

67 years old and remember the Wheatstone Bridge

I wish you came here a few months back!!

 

[Martaine2005]

Hi paj,
It definitely sounds like the dashcams' wiring needs shielding. Or more shielding.
I have read that a 300mhz ferrite 'snap on' core can do the trick.
Apparently, it's something to do with the initial bands given to DAB and then extra bands afterwards.
Those extra bands are the ones being reported as getting interference from certain dashcams.
Also, if your radio antenna is at the rear window (normally the front), you could always fit another antenna elswhere on the car.
But try shielding the cable properly first. Or buy another cable that is already shielded.

Martin

 

[PAJ]

Hi paj,
It definitely sounds like the dashcams' wiring needs shielding. Or more shielding.
I have read that a 300mhz ferrite 'snap on' core can do the trick.
Apparently, it's something to do with the initial bands given to DAB and then extra bands afterwards.
Those extra bands are the ones being reported as getting interference from certain dashcams.
Also, if your radio antenna is at the rear window (normally the front), you could always fit another antenna elswhere on the car.
But try shielding the cable properly first. Or buy another cable that is already shielded.

Martin

Thanks for the prompt advice Martin. I will certainly try additional shielding, but the problem also occurs even when no external power supply near, running on its own short-lived rechargeable battery. Also there if satellite camera is not connected (it plugs into main camera) so nothing to do with that wiring.
Your idea of the rear window element being replaced by a seperate antenna is a good one. It must be the rear one because I have an identical camera in the front screen which causes no problem at all. The only difficulty is access to the antenna connection to substitute the replacement.

 

[Martaine2005]

All electronic devices have 'noise'.

Have a read on the Wiki about electronic noise and interference. Here.

Martin

 

[PAJ]

HI Martin
I have had a read-up and now see that anything with any kind of current will give off some degree of noise.
I had already thought about using a Faraday cage but it appears that any gap could render it ineffective so probably an aperture for the lens would defeat it.
I will buy a heavily screened usb power cable tomorrow (Monday) and also a snap-on ferrite core, which I see needs to be on the camera end of the cable, and power it from an adator rather than the supplied lighter-socket plug. I don't see how it could hurt to put a ferrite core on both ends of the cable.
I will let you know the result.
Thanks
PAJ

 

[Martaine2005]

using a Faraday cage but it appears that any gap could render it ineffective

Yes, including your phone, radio, GPS etc too.
Have a go with the ferrite cores first (cheapest) then the shielded cables.
You will get to the bottom of it eventually.
Good luck and don't forget to let us know how you get on and what worked for you!!
Good luck.

Martin

 

[PAJ]

Hi Martaine
Apologies for delay in replying: sadly the "fully shielded" cable I bought and then triple wrapped around a clip-on ferrite ringat the end at the camera was all in vain.
I think the only answer is your plan B: use a second antenna. The only problem is how to connect it.
Again, thanks for your input and I am still open to any other suggestions.

 

[Martaine2005]

That's a shame. Sorry it didn't it work out.
Can you get access to the back of the radio in the car?
That's where the aerial input will be.
You could always put an external on the roof in the centre. Front or back.
If it's at the back, you could splice from the original.
But I would have a play first before drilling etc.

I wonder what signal/noise the cam is emitting. The shielding should have worked really.
Let me have a read and get back to you later.

Martin

 

[Martaine2005]

Hi Paj,
I just called Smart Witness and explained your problem.
They say they are not aware of this and it's a first. (Yeah right).
They are finding out what they can and will ring me back either later before 6pm or tomorrow.
I shall get back to you when they have called me.

Martin

 

[Martaine2005]

Hi Paj,
Just had a call back from Smart Witness technical support.
It would appear that your issue is not new and happens in some other cars too.
Apparently there engineering team are trying to fix the cause of it. They don't know how or why yet..

I think it's back to the drawing board for now.
But one good thing came from this...
There number is those horrid 0844's
But when he called my mobile, I got there local number displayed.
020 8689 9999
You can cheaply pester them on a weekly basis now

Martin