On Thu, 21 Apr 2005 09:22:27 -0700, Keith Hughes
wrote:


2. If the 12V device (VHF IIRC) is a significant load, you can always
build a simple voltage divider (the VHF should be input voltage tolerant
enough to handle the voltage sag during transmission) and run from both
batteries. The overall battery draw will, of course, be somewhat larger
since you'll dissipate heat in the dropping resistor. If multiple
devices are used, however, this approach quickly becomes problematic.

Keith

A series voltage dropping resistor may work for some devices where the
current draw is constant, but it _will not_ work for a VHF radio. The
radio will only draw a few hundred mA on receive when squelched,
somewhat more when actually receiving, and a few amps when
transmitting - there is no way a simple resistor can keep the supply
voltage to the radio within acceptable bounds with that current
variation.



--
Peter Bennett VE7CEI
email: peterbb4 (at) interchange.ubc.ca
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