Q NT9N asks, “I’d like to install a 40-W, 2-meter mobile transceiver in my car. Why can’t I tap the +12 volts from the fuse block inside the vehicle instead of going directly to the car battery? Getting a wire through the firewall seems difficult and I don’t want to drill holes. Any ideas?”
A Even though you could indeed power a 40-W rig from the fuse block, there are still benefits to connecting to the car battery directly. By obtaining your power at the battery you reduce the possibility of causing voltage drops at various points in the car’s electrical system—drops that might cause sensitive electronics to malfunction. In addition, the low internal resistance of the car battery may act like a filter capacitor and short any stray RF to ground instead of allowing it to propagate through the rest of the wiring.
Getting through the firewall to the battery isn’t as hard as it seems. You should be able to find a little rubber plug about the size of a bottle cap (or larger) on the firewall that can be removed or sliced open to allow your power cables to pass. You may also be able to snake your power cable through a grommet used by an existing wire harness. Just be careful not to damage the other wires.
There is much more information available. Mobile installation subjects are covered in the ARRL Handbook and the ARRL RFI Book.
From QST March 1999
