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The SGC Building, 13737 S.E. 26th St. Bellevue, Washington 98005 USA
P.O. Box 3526, 98009 Tel: (425) 746-6310 Fax: (425) 746-6384
© 1997 SGC Inc.
High peak current is an important consideration if you are planning to operate in the voice mode. But if you
are planning to operate in the data mode or will be using the transmitter on a more continuous basis, output
capacitance is less a factor than how heavily built the transformer in the power supply is.
In virtually all mobile power supplies, the source of power is the alternator or generator system of a vehicle and
the battery. You should consider several principals of good design that affect the mobile environment when
operating from a mobile position on the HF bands.
First, HF requires quite a bit of power when transmitting. Although you can use a single battery to power both
the vehicle and the radio, SGC recommends that you install an additional battery in all cases where this is practical.
The reason for this installation is that the output voltage from a battery drops as the load increases. The more
reserve current capacity, the lower the voltage drop under high intermittent power demands.
On occasion, you will find that some vehicles operate with 24 volt DC power in the mobile and marine
services. Two approaches can be taken. First, you can install a 24 to 12 volt converter. This converter is usually
expensive. A much less expensive approach is to look for a 24 volt system that uses two 12 volt batteries in series. If
you are fortunate enough to find this type of system, simply connect the 12 volt batteries with the negative post of
one battery tied to ground, the positive lug of that battery connected to the negative terminal of the second battery,
and the positive lug of the second battery as the + volts terminal.
The extra battery will be of assistance when your vehicle is not running; then you will be able to operate the
transceiver for a varying amount of time (depending on the power output of your transceiver and how much time
you are transmitting). However, your alternator must be able to provide the power to operate everything in your
vehicle. If you are transmitting continuously, the heat is being blown by the fan at full blast, and the high beams are
on, you might be consuming more power than the power system is capable of producing. If this is the case, the
accessories will operate from the batteries until they have drained. Then, the transceiver will operate at a lower
output, the heater will produce less warm air, and the lights will probably dim. After you turn off the vehicle, you
will find that it won't start because you have drained the battery.
As a result, it is important to check the current drain of the transceiver during transmitting, plus the total current
drain of the other vehicle accessories. Add these figures together and see how they compare to the current output of
the alternator. If the drain is anywhere above just under the output of the alternator, then you should purchase a
higher powered alternator, such as those that are made for high-power car-stereo systems.
MOBILE POWER SUPPLIES
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