AMX TXC16 Plus Specifications download pdf (Page 45)

SG-2000 MANUAL 38

The SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA

10.4 Mobile Power Supplies

In virtually all mobile power supplies, the source of power is the alternator or generator

system of a vehicle and the battery. There are several principals of good design that

come into play in the mobile environment which you should consider when going

mobile on HF.

First, HF takes a lot of power on transmit. While you can use a single battery to power

both the vehicle and the radio, SGC recommends the installation of an additional

battery in all cases where this is practical. The reason for this 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.

Some vehicles operate on 24 volt power in the mobile and marine services. There are

two approaches which can be taken. First, you can put in a 24 volt to 12 volt converter.

This is usually expensive. A much less expensive approach is to look for a 24 volt

system which uses two 12 volt batteries in series. If you are fortunate to find this type of

installation, simply use the 12 volt battery which has its negative post tied to ground

and the positive lug at 12 volts above ground. Never use the battery on the other half!

In mobile operations, the biggest problem you will run into will be noise. While noise

sources are easily found in fixed locations, in the mobile environment, including marine

applications, noise sources may vary depending on engine speed and other variables.

Mobile power sources are notoriously noisy. Generators and alternators are only part

of the problem which you will encounter. The presence of ignition sources including

the coil, distributor and the spark plugs complicates matters. The best solution is to use

a diesel engine and eliminate the ignition issue entirely.

When you are installing an HF system in a mobile setting, one of the best pieces of

troubleshooting equipment you'll find is a small portable AM broadcast band transistor

radio. With this radio, tuned to the highest end of its range (usually around 1600 KHz),

you can use it as a hand-held noise probe to quickly identify sources of noise.

Good design practice dictates putting capacitors across the alternator or generator

output and across the primary leads to the coil/distributor and at fans and other

electrically operated devices. We've even found cases where power windows in a

vehicle would cause RF “hash” on receive. The point is that you almost never have too

many capacitors.

Ignition wire can be both a source of grief and a source of joy, depending on the vehicle.

Most vehicles in North America come with resistor-type ignition wiring. This wiring

has about 10 K ohms of resistance from the distributor to the spark plug. If you have a

vehicle with solid ignition wiring and you experience RF “hash,” a 10 K ohm, 10 watt

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AMX TXC16 Plus Specifications Page 45