Optical Isolation

[gkgsr]

Hi All,

I'm dealing with TV tuners in my car, and im getting a weird hum from the tuner, when watching TV. The pitch of the hum changes with the station im watchin, i.e 1 station is higher MHz to pick it up it goes up and down with that..

If i unplug the aerial it is fine, but as soon as its tuning something its making lots of electrical noise through the amps.

Just wondering if theres any circuits available using some form of opto isolators? Also I'd need a 2 input, 1 output switch box made, maybe I can combine the 2.

ANy other opinions?

tim.

 

[audioguru]

You can't use an opto-isolator with the very high frequencies at the antenna. If you use an opto-isolator to pass the audio to your amps it will also pass the interfering sound.
You say you have more than one tuner, maybe they are interfering with each other.

TV in your car? Do you live in your car?

 

[Optikon]

TV in your car? Do you live in your car?

This totally pegs your age Audio, DOH!
:lol:

 

[audioguru]

TV in your car? Do you live in your car?

This totally pegs your age Audio, DOH!
:lol:

Sure I'm an old geezer. I go places in my car, I don't live in it nor watch TV soaps in it. My DVR records all the stuff I want to see when I want to watch it in the comfort of my home.

 

[gkgsr]

Yeah I have a TV tuner in the car, but i also have to decide whether to play xbox, or use my full desktop computer......

But the problem lies in the tuner, the computer and xbox aren't hooked up at the moment. IU've swapped the actual tuner where I got it, mayb theres a fault in the cables/aerial...

Any other ideas?

Cheers,
Tim.

 

[panic mode]

how exactly is aerial connected?

 

[Gorgon]

Hi All,

I'm dealing with TV tuners in my car, and im getting a weird hum from the tuner, when watching TV. The pitch of the hum changes with the station im watchin, i.e 1 station is higher MHz to pick it up it goes up and down with that..

If i unplug the aerial it is fine, but as soon as its tuning something its making lots of electrical noise through the amps.

Just wondering if theres any circuits available using some form of opto isolators? Also I'd need a 2 input, 1 output switch box made, maybe I can combine the 2.

ANy other opinions?

tim.

Hi Tim,
One thing I can think of is that you create a sort of ground loop with your antenna connection. If you isolate the DC from the screen of your cable from ground(body), just connect it with a small capacitor to get the hf ref.

This is just a wild guess but you never know. By the way have you tried to disconnect the antenna to the car-radio, just to see if that makes a difference?

TOK

 

[panic mode]

is that you create a sort of ground loop with your antenna connection

exactly, in a car everything connects to chasis which means that current is flowing through it all the time. receiver is probably also powered from car's 12V system and as such it is not isolated. if the coax from antena is touching any part of chasis (electrical connection, not mechanical) it will create ground loop, uncontrolled oscillations and problem described...

 

[gkgsr]

Well I don't actually have any form of head unit, only the computer with the touch screen..

The antenna for the tuner is a small dipole lookin thing, which has a standard push in type antenna connection. This runs through about 3 metres of RG59 coax, to the antenna. Antenna has a magnetic base, which sticks on the roof.

I'm gonna attempt to connect it through the line-in on the computer maybe it will filter it out :S

Also, will wrapping all of my cables in aluminium foil be good for them? i.e extra shielding?

Cheers,

Tim.

 

[audioguru]

The computer with the touch screen is causing your TV interference.

 

[gkgsr]

Well the touch screen is completely unplugged at the moment, just the amp and tv tuner going, still getting the noise.. maybe a faulty aerial or something similar.. ill see what i can work out;

Thanks for your help so far.

Tim.

 

[audioguru]

Maybe your amplifier uses a switching voltage converter that is sending RF interference.