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Author Topic: Somewhat OT, but involves video transmission in a car.  (Read 7959 times)

Posts: 587

« on: April 25, 2014, 02:22:44 PM »

Hi I was wondering if you mobile operators can help out here.
I have installed a wireless backup camera in my car.  This uses a license plate type camera and transmits a 2.4 gHz signal to a receiver on my head unit (radio).  Now, when the car is turned on accessory (no engine running) and the transmitter and camera are operated off an external battery then everything is perfect.
Next, if the transmitter is run off the backup light (12V when in reverse) and the engine is not running, then there seems to be a fair bit of interference and noise generated.  Thus it would seem that the noise is coming over the 12V line.
When the engine is running then it's almost impossible to see the signal, it's full of noise and it freezes occasionally.
The transmitter / receiver is of course cheap stuff made in China so I'm sure that there is little consideration made to noise filtering.
This plus the fact that my engine is in the back of the car doesn't help.
So how do I go about dealing with this?  I presume I need some type of power filter and possibly some type of ferrets on the video cables?

Thanks for any help, Tom va2fsq


Posts: 10248


« Reply #1 on: April 25, 2014, 03:39:13 PM »

Unfortunately, a lot of stuff from China doesn't meet Part 15, or Canada's equivalent. Presented with the exact problem (I had purchased one as a Christmas gift for my next door neighbor), I junked the unit, and replaced it with a wired one. Problem solved!


Posts: 1794

« Reply #2 on: April 25, 2014, 04:26:18 PM »

I find it interesting as 2.4ghz is line of sight and the transmitter is on the back of the car
down low and the RX (screen) is upfront and neither are line of sight to each other.
It would likely work as as long as there is a car or trash can or the like behind you as
a reflector but in the clear its going to be crappy.  Likely that is more a factor then
noise on the power.

Also most of the stuff in there runs on 5 or 3.3V so 12V is filtered by the power
supply needed to get to that voltage internally.

Now ignoring CE/FCC and Canada's radio agency rule for a moment.  The whole
idea of using 2.4ghz to get from the back of a car or truck to the front is just foolish
and unreliable at best.


Posts: 15019

« Reply #3 on: April 25, 2014, 04:51:40 PM »

There is so much plastic and glass in cars today that it wouldn't surprise me to be able to get a 2.4GHz signal over that short distance. There's probably plenty of reflected signal as well.

I assume that in order to get your backup lights to come on you had the ignition switch turned on but didn't start the engine. That probably means that the various computers in the car were running (a potential cause of noise on the power line and/or 2.4GHz interference). Did you try the external battery on the camera/transmitter with them in their final location? Did you try it with the ignition switch on? The goal is to determine if the interference is getting into the system via the 2.4GHz receiver or via power wiring or a ground loop in the video wiring between the camera and the transmitter. The power line should be easy to filter externally but if vehicle computers are generating 2.4GHz signals it will be a much bigger problem.

You could also try moving the receiver/display away from the vehicle and running it from a battery to determine if the interference is getting into the transmitter or into the receiver. If you have the camera/transmitter in place, powered from the backup light, and the engine running but the signal is clean with the receiver/display on battery away from the vehicle then that tells you that the interference is entering the receiver directly, either via its antenna or power wiring. If you move it into the vehicle while still on battery and the interference comes back then its getting in via the antenna. If its clean until you hook it to vehicle power then it's getting in via the power line so you can add a filter there.

Bob  AA4PB
Garrisonville, VA

Posts: 587

« Reply #4 on: April 25, 2014, 06:34:27 PM »

Yes, funny how one thinks about radio signals from a ham perspective when one is working on ham equipment and then one forgets basic principles when working on something else....that's me.
a 2.4 gHz is line of sight and won't go through solid steel! Otherwise we'd all be in bad shape every time we used the microwave for something lol.
So all the signals are reflected for sure.  It's directly behind the engine so between it and the front dash there's several feet of aluminum followed by the metallic radio itself. I can relocate the transmitter a bit to be higher up and bypass the majority of the metal of the engine.
Interestingly, when I tested it out of the vehicle on it's own battery, it was in front of the car.  There it had a plastic bumper to go through and the front firewall.  Not much else in the way.  Also interesting is that there was no noise generated at all with the ignition on.  Therefore the noise that was being picked up seems to be only when the transmitter is attached to the car's power.  At least when the engine is not operating.  On the other hand the signal strength was usable.
Not so when the engine is running though.
It might be worth a try to filter the supply and see the results.  Any suggestions?


Posts: 1315

« Reply #5 on: April 28, 2014, 07:17:35 AM »

just because it came with a license  mount doesnt mean you musy use it that way.
I have one that the camera and transmitter  are seperate units and can be mounted up in the window.
also the one at the license gets dirty  fast.

Posts: 571

« Reply #6 on: May 08, 2014, 09:31:06 AM »

Gonna be dumb here but how much vibration does your engine give the video camera? Not questioning EMI from the car but if it's that much worse with the engine on at that frequency makes wonder. Any computer rfi would be obvious with just the electric on, not the engine, and you demonstrated that was the case.

Posts: 273

« Reply #7 on: May 08, 2014, 06:28:11 PM »

Just out of curiousity

What are you driving that has the motor in back??
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