jsg@aero.ARPA (Jeffrey S. Gruszynski) (10/16/85)
Ignition noise on stereos: Ignition noise is wideband electromagnetic interference (EMI) generated by automobile ignition systems. It is caused by a combination of electrical interactions in this system. The necessary factor for this EMI is the presence of a spark gap in the circuit. Electrical sparks and arcs (1) all have negative electrical resistances, i.e. an increase in current produces a decrease in voltage across the gap. This means that electrically (and mathematically) positive (garden variety) resistances can be reduced or cancelled. Positive resistances include resistances in wires and components. This is not to say that no power is dissapated when the resistances are cancelled, but rather the resistance _looks_ like zero to other components in the system. This is the problem, the other components. The ignition system has stray inductances (L) and capacitances (C). When the resistances of a LC system are removed the system will ring at characteristic resonance frequencies. This is the ignition produces interfering RF. It has formed an oscillator. For a variety of reasons the RF is wideband. These include: distributed nature of the LC's and random fluctuation of spark length (i.e. negative resistance) over time. Based on this information and a little knowledge of RF we can conclude a few things: Cause: The RF is being received by the radio itself. Solution: 1. Reduce RF generation. Use resistor plugs, suppression wire (introduces "+" resistance to cancel "-") 2. Reduce RF emissions. Shield plugs and wire Cause: The RF is being received via a ground fault. Solution: 1. Reduce RF sensitivity of power lines Filter power supply. Only DC should pass. Add a low-pass filter. Make sure ALL audio equipment grounds connect to single point with the shortest length of power cable. (2) (1) Sparks and arcs are members of a class of phenomena that result from electrical breakdown of gas and subsequent conduction through the plasma. Arcs are the low voltage/high current version. Sparks the high voltage/ low current version. (2) If not done, the length of car body or extra cable will act like an antenna. Electrically this is the same as adding an RF voltage source between the _equipment_ ground and the _real_ ground. You ground is not at ground! Interestingly, your ignition system works exactly the same way as a spark-gap radio transmitter of early radio fame. good luck! jeff
hrs@homxb.UUCP (H.SILBIGER) (10/29/85)
I have an ignition noise problem that is clearly RF related, i.e. is not audible during tape operation. The problem started after I had the car tuned up. I have all the usual: resistor plugs, wires, distributor condenser etc. What could have been done during the tune up to cause this interference to start? Herman Silbiger ihnp4!homxb!hrs
gvcormack@watmum.UUCP (Gordon V. Cormack) (10/30/85)
> > I have an ignition noise problem that is clearly RF related, > i.e. is not audible during tape operation. The problem > started after I had the car tuned up. I have all > the usual: resistor plugs, wires, distributor condenser etc. > What could have been done during the tune up to cause this > interference to start? > > Herman Silbiger ihnp4!homxb!hrs 1. Are you sure they put in resistor plugs? 2. A spark plug wire could have been broken. Check the continuity. 3. There is a noise suppression capacitor between the positive coil connection and ground. This could have been disconnected when the tune up was done. (this may not exist with electronic ignition.) 4. One or more of the spark wires may be disconnected either at the distributor or spark-plug end. 5. A spark plug may be broken internally (unlikely). 6. The rotor or distributor may have eroded or the insulation on the wires become weak. These are not caused by the tune up, but the stronger spark after the tune up may cause these weaknesses to make more noise than before. To help narrow down the source of the problem, try to estimate the frequency of the ticks. At idle, if the ticks are approximately the same speed as a clock, look for a problem with one plug or the wire leading to one plug. If the ticks are much faster (almost a buzz), look for a problem in the common part of the circuit (coil, coil wire, distributor) or else a problem that is uniform for all cylinders (e.g. non-resistor plugs).
axa@panda.UUCP (Andrew Alvino) (11/07/85)
*** REPLACE THIS LINE WITH YOUR FORD ***
The verdict is in on the ignition noise that I was having in my Bronco II.
The problem was a rpm related "pop pop pop" on the *** RADIO ONLY ***.
The answer from Ford and Alpine... " I don't know what it is."
The place that installed my radio had 2 fords to work on for a week.
An Alpine tech and a Ford tech worked on these vehicles and they were
stumped. I was told by the guys in the shop that they even went as far as
to check the fuel pumps. They checked everything. But they could not
find it. If anyone knows about this problem and a possible answer (all of
the normal answers don't work) give me the word. Any other Ford owners
out there with this problem?
Andrew Alvino
GenRad, inc.pagiven@drutx.UUCP (GivenP) (11/08/85)
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Check the alternator/voltage regulator (combined into one unit, at
least on GM cars) for a source of radio noise. Just disconnect the
alternator fan belt and see if the noise stops. Rectifier circuits
can get very noisy (RFI kind) when diodes break down.
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Paul Given {ihnp4, houxe, stcvax!ihnp4}!drutx!pagiven
AT&T Information Systems Laboratories
11900 N. Pecos, Rm 1B04, Denver 80234 (303)-538-4058
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