radio static on AM
Thread Starter
Le Mans Master
Joined: Mar 1999
Posts: 6,744
Likes: 1
From: delmont pa
Cruise-In I Veteran
Cruise-In II Veteran
ignition noise on AM
why does the AM on my truck radio have no ignition noise at idle and at wide open throttle but has it at part throttle ? :confused:
[Modified by clem zahrobsky, 8:53 AM 8/14/2001]
[Modified by clem zahrobsky, 8:53 AM 8/14/2001]
Burning Brakes
Joined: Aug 2000
Posts: 883
Likes: 2
From: Hilton Head SC
Re: ignition noise on AM (clem zahrobsky)
Been thinking about a similar issue for quite some time myself. My AM has almost no noise at cruising speed, but it gets louder when I lift off the gas pedal. My theory, so far, is that it's alternator noise (not ignition) and that getting on and off the gas changes the load on the alternator. I have new silicone plug wires, resistor plugs and all the factory shielding in place except the plug shields. I am missing both the suppression capacitors (coil & steering column) and can't find replacements. I'm really curious as to what some of the electrical experts have to say and would love to find a source for replacement capacitors.
[Modified by JSB69, 9:40 AM 8/14/2001]
[Modified by JSB69, 9:40 AM 8/14/2001]
Instructor
Joined: Aug 2001
Posts: 130
Likes: 0
From: Yorba Linda, CA
Re: ignition noise on AM (clem zahrobsky)
Clem,
I'm no RF engineer, but I believe its related to the changing of frequencies of the EMI (electromagnetic interference) that the engine electronics (ignition and charging circuits) produce. AM is a simple amplitude modulation transmission scheme in the 540-1600 kHz range. Any change in amplitude of a frequency in that band and it will be “heard”.
Any EMI (or harmonic frequency of that EMI) will disturb the radio reception. When accelerating the EMI frequencies are changing quite rapidly, versus at idle and WOT they are more at a steady state and possibly farther out of the AM band.
Don
P.S. That's what all the capacitors do, they help filter the RF noise from the power lines.
[Modified by Don O'Connell, 12:54 PM 8/14/2001]
I'm no RF engineer, but I believe its related to the changing of frequencies of the EMI (electromagnetic interference) that the engine electronics (ignition and charging circuits) produce. AM is a simple amplitude modulation transmission scheme in the 540-1600 kHz range. Any change in amplitude of a frequency in that band and it will be “heard”.
Any EMI (or harmonic frequency of that EMI) will disturb the radio reception. When accelerating the EMI frequencies are changing quite rapidly, versus at idle and WOT they are more at a steady state and possibly farther out of the AM band.
Don
P.S. That's what all the capacitors do, they help filter the RF noise from the power lines.
[Modified by Don O'Connell, 12:54 PM 8/14/2001]
