[RFI] 4 Runner Fuel Pump

Bill Turner w7ti@dslextreme.com
Wed, 09 Oct 2002 06:58:39 -0700

On Tue, 8 Oct 2002 22:29:35 -0700, Dennis Vernacchia wrote:

>I also tried outiing a 250 uH choke in each lead and also caps to ground
>on either side of choke and all I can do is INCREASE noise (hash) to S9
>when caps are on far side of choke away from pump.


Sometimes simply adding a capacitor can actually increase the
noise, as you have found.  This happens when the circuit has a
fairly high Q to begin with and the capacitor merely changes the
resonant frequency.  Caps alone work well when the circuit has a
relatively high equivalent series resistance, then acting like a
low-pass RC filter.

Try adding a capacitor with a small value resistor in series with
it, on the order of 10-100 ohms or so.  Some experimentation will
be needed.  You might temporarily connect a potentiometer in
place of the resistor and then install a resistor when the
optimum value is found.

73, Bill W7TI