Rectifier Bridge

Fig. 7. The charging system for late-model GM cars.

that more spurious harmonics will be generated along with more spurs in the audio range. This will affect the "purity" of the whine you transmit. Get the hint? If your whine suddenly changes its characteristics, check your alternator diodes! Hopefully, you will have removed this annoying signal from the air long before any diodes break down.

Much has been said, but little written regarding ways to reduce the spurious transmission of whine. The most effective way that I have found, borne out by automotive people I've contacted, is to insert a properly rated choke in series with the "A" line to your radio. A value of about 20 mH worked for me. The most flagrant error made is to attempt to use a standard CB-type choke. These things are rated at only 2 Amperes. Most amateur equipment draws up-

Photo B. Result of shorted diode in an alternator. Photo C. Result of open diode in an alternator.

73 Magazine • January, 1981 147

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