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Silent Night

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"My boat is the only one in the fleet that can’t hear Herb Hilgenberg’s Atlantic weather report on SSB. Even though I turn off my circuit breakers before I tune in, I still get noises that affect my reception. I had a technician come aboard, and when he disconnected my batteries from the circuit he could hear Herb’s transmissions loud and clear on his portable SSB. But when he reattached the DC power he wasn’t able to isolate the noise source. Any ideas?"

-- Robert Antrim , via e-mail.

Gordon West replies : It’s not uncommon to have this noise, and it can have a significant effect on incoming traffic. Most likely the noise source is a connection to the batteries that comes before both the circuit breakers and the main-battery selector switch. It’s the tap-off line for a microprocessor energy counter that monitors your system’s volts and amps. It’s always on, and, if it has LED readouts, they can add more noise because the LED chopper circuits illuminating each segment operate like tiny radio transmitters. Even though they are built within specs, these voltage monitors produce noise when they are operating.

To test whether this is your noise source, first tune your SSB to a WWV time signal at 10 MHz. Then remove the voltage-monitor wire running from your battery terminal. If the SSB noise goes away, you’ve located the noise source. Of course, disconnecting the line means that you no longer have any voltage calculations. To minimize that time period, I suggest that you install a switch in the monitoring-system line that you can turn off when you’re trying to receive distant signals on your SSB.

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