The radio interfere problem on my Celsior

 

My car generates the ignition noise and it interferes the radio equipments.

As long as I listen to AM radio stations nearby, it is not serious but once I try

to catch short wave radio signals from abroad, it is very annoying and serious.

May be I expect too much but I want to improve it.

As I check the car using a short wave radio, the noise is coming out from the

cables connected to the ignitions coils. As I see the circuit diagram, there is

only a single capacitor connected to the 12V line to each ignition coils. Below

is the almost whole part of the ignition circuit and the capacitor is at the top

right corner.

 

Below is the enlarged top right corner.

 

The actual engine has this capacitor 0.47uF/250V below.

This is a film capacitor and it works mostly OK at lower frequencies such as

less than a few MHz. But it increases the impedance higher than that.

 

I already have started the experiment. In order to keep the impedance lower

at HF and VHF range, I added ceramic capacitors as is shown below.

I happened to use 5 of 0.0022uF since I only had them in my parts box.

The addition resulted about 10dB better than before at 10 MHz. This improved

the situation but 10dB was not enough for me. May be I should add some more

capacitors or add a series impedance to 12 live indicated by a red line below

for my next experiment.

 

My experiments will be continued.