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Video Interference

Pete_Repeat
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Pete_Repeat Enthusiast

Pete_Repeat

Posted
Posted

I'm surprised I couldn't find a topic in this but I did try.

My V36 2008 with Sat nav came with the rca (composite) plugs in the centre console. I tried a mirabox and my go pro and both have minor picture interference (lines and not overly clear) unfortunately.

Sounds is fine however.

Interference is the same with engine running or just on accessories.

I'm thinking a filter at the input would only help if it was from the source.

Anyone else have this.

I'm either thinking it's not a great connection and to resolve it.

Or tap into the component (rgb) input but this involves the radio out I believe (???). Would this improve the picture anyway?

Or preference would be a filter in the centre console but have my doubts this will help.

Suggestions? I want as clear a picture I can get from a miracast box but don't want to pull the radio out if it isn't likely to help much.

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Pete_Repeat Enthusiast

Pete_Repeat

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Posted (edited)

No one got any comments? I thought someone would either comment to say they have perfect picture through composite (single yellow rca video) or component (rgb). Or more hoping that others might have had the same interference as me but fixed it..

Key point is it's only the video signal that has interference and it is the same with engine on or off. And only appears when a video source is plugged in (can't see it on black screen).

I was hoping get feedback before pulling the centre console out and checking connections as that's the last resort. I'll likely have to pull the unit out as well which is what I was trying to avoid.

Edited by Pete_Repeat
The Max Mentor

The Max

Posted
Posted

What you're seeing there is video hum. I have it on mine as well, just haven't been bothered to get my hands on a humbucker (aka isolation transformer) to resolve it. It's highly likely because there's a ground loop happening between the mirrorlink device and head unit.

If/when I do end up pulling my finger out, the plan will be to hardwire it into the cable path within the centre console so that it doesn't take up any valuable space inside the armrest compartment.

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Pete_Repeat Enthusiast

Pete_Repeat

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Thanks for your response.

The weird part is that my go pro running off its own battery does it.

So I guess the ground loop must be in the car electrics and the ground of the composite signal (rather than the sources power)

I made a point of using the go pro to isolate the ground of the power source but perhaps I had one of those moments and plugged the usb in as well.... Don't think so but I've done stranger things ha ha.

To be continued tonight.

The Max Mentor

The Max

Posted
Posted

I made a point of using the go pro to isolate the ground of the power source but perhaps I had one of those moments and plugged the usb in as well.... Don't think so but I've done stranger things ha ha.

Let us know then because I was thinking about your mirrorlink device, which is powered by the car. If it's happening on a completely ground-independent device such as your GoPro on battery power, then it suggests my ground-loop theory is wrong.

Are you able to select NTSC over PAL? That is usually the reason for the lines isn't it?

Nope. If it's the wrong colour system, you would have an unstable (as in scrolling) picture as well as no colour.

Reason for this is because PAL has 625 lines of resolution whereas NTSC has 525 lines. So if you have 100 extra or fewer lines than what the display device is expecting, the end result is that it can't lock onto what is meant to be the true end of the field and you get the resulting perpetual scroll.

Then you have the colour subcarrier, which for PAL is 4.43MHz while NTSC is 3.58MHz. If they don't line up, you simply don't get the colour information coming through, hence why it's a black and white image.

I set up my Mirrorlink device to operate on NTSC, since that's the Japanese standard. The herringbone pattern on the screen is definitely video hum though, from my past experiences.

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Pete_Repeat Enthusiast

Pete_Repeat

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Posted

I'm gonna try the gopro again and make sure I didn't plug in the usb charge by habit... Hope I just messed up and it is ground loops as mentioned.

Was suggested by someone else to measure the outer of the rca input to ensure there is no voltage there, and if not (which it shouldn't) then try grounding it directly to see if that changes anything. Also have one of those ferrite cores to try on the power source..

Pete_Repeat Enthusiast

Pete_Repeat

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Posted (edited)

Hmm. Well you were right. I intentionally got the go pro to isolate power issues like ground loops or any high frequencies while the car is running... But must have subconsciously plugged the power in as well as there are no more lines running on battery tonight.

Interesting part is, the more rca plugged in the worse the interference lines get. Which seems to back up your theory of ground loops huh. And it's no worse with engine running or not so isn't noise due to the alternator.

Looks like a ground isolation or something is in order.

Thanks for the help. I'll report back if I find an easy but cheap solution.

Edited by Pete_Repeat
The Max Mentor

The Max

Posted
Posted

Good humbuckers aren't really cheap. Expect to pay anything around $60 for a mediocre one and around $130 for a decent one.

If you are feeling daring, you could use an audio ground loop isolator but the impedance of the transformer being mismatched to the video source may end up working against you.

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