'96 4.0 2+2 - Radio cable

What is the purpose of the small circuit board with the blue antenna wire and the yellow 12v wire? Noise suppression?
Installed it was in a little black plastic box.

 

Someone must have some idea what it's for!

 

I know electronics, although I haven't seen this part before and can't tell what it is for. Seeing the other side of the circuit board would help. Also, where exactly this connects to?

 

Is this behind the radio or at one of the speakers, or one on each speaker?

 

It's a noise filter. A coil (transformer in this case) in series will allow DC uninterrupted but look like a high resistance to AC.

 

A noise filter coil has only two wires. You cannot use a transformer for DC, it simply won't transform anything. So why this board has 6 wires?

 

It's the cable coming out the back of the radio.
The Blue wire is the antenna and just goes through a resistor.
The Pink/White wire is the phone interrupt (I think) and goes to whatever the little black component is. There are no markings on the component.
The Yellow wire is +12v and goes through the transformer to one leg of the black component ( I'm thinking it must be some kind of switch).

 

You can use a transformer as a coil, a transformer is 2 coils separated by an insulator. You just wire the DC to one side of the transformer so the DC goes through the primary and the secondary is unused cheap and effective.

DC will pass unimpeded and any AC will be attenuated. The black component looks like a capacitor but I can not read what is written on it.

You can increase the filtering by adding a capacitor across the transformer. A large Electrolytic 200uf 100v in parallel with a small 0.01uf ceramic.

 

I think that is an aftermarket piece. I've not seen one like that before

 

Yes you can, but if you were to manufacture a bunch of filters you would not order more expensive transformers instead of simple coils.
No, this will not increase filtering (except for tuned filters used for high frequency, not the case here). Capacitor can be used to suppress the voltage spike which occurs when voltage source is disconnected. (The same effect is used in ignition coils to induce spark.) BTW, all units named after person are uppercase. Thus, it is V, W, A, Hz, etc. (Not v, w, a, hz.)

I was hoping the other side helps to understand what this board is for, but it wasn't much help. Elements with three legs are usually transistors or thyristors. (The latter has not much use in DC circuits.)

 

You would be surprised what I have seen manufacturers of very expensive electronics do in my 35years repairing highend test equipment, military and avionics.



Any LC filter can be tuned for any frequency it can be from a few Hz in a speaker Xover to the fine tuning circuit on the output of a YIG oscillator at a few GHz.


The capacitor will increase the slope of the filter, if we use a speaker Xover as an example a simple inductor in series as a lowpass filter will give a rolloff of 3dB per octave if you add a capacitor across the speaker the rolloff will double to 6dB/oct.

 

Its probably not a transformer but a coupled inductor - used to reduce common mode noise.

 

Hi Guys

I know absolutely nothing about Auto-Electronics but I wanted to swap out the Original Stereo for a much more modern one on my Car 'Cherry Blossom'

Which was surprisingly very easy to do, so this could viewed as a 'step by step guide' for anyone who is thinking of doing the same

But referring to your Question Pete (Petemohr) I did have to cut off the 'noise suppressor' to give me a bit more room to fit the New Stereo

Which didn't make any difference to the Sound Quality, or not that I was able to detect, where the reason that I mention it is that this 'noise suppressor' only had one wire

Which is on Page: 61 of my 'Cherry Blossom' restoration thread, which happened to be the very day that 'Cherry Blossom' was finally finished and put back on the road

Link to Page: 61 https://www.jaguarforums.com/forum/x...122634/page61/

(As an aside this also includes one of my favorite reggaeton dance tracks)

 

Even a common garden variety transformer will help filter common mode noise through its parasitic capacitance. CMN is a bugger because it is the same polarity on both conductors it does not present a potential difference to the load, so its only path to ground is via parasitic capacitance.



CMN is not really an issue in this type of installation, even the cheap power supplies have CMMR (common mode rejection ratio) of 100dB which is 100,000:1. CMN can be a real issue in high speed data and low signal audio like a turntable.



I suspect the circuit is a noise filter either LC or CL to filter alternator whine, which can not be filtered with just capacitance to ground.