Technical information

will be skeptical. So let us show you how you can get a sig-
nificant increase in gain by simply using a QMS-3-500 com-
pared with any other 3.5 to 30 MHz system:
• Most antennas are so heavy that they are mounted on the
bumper of a vehicle. Because of this location, about a
third of the antenna is less than a foot from the
grounded body sheet metal. This is equivalent to a
capacitor of 25 to 100 pico Farads shorting your anten-
na. QMS, mounted high on the side of the vehicle, gains
3 to 6 dB.
• Body sheet metal prevents the antenna from radiating
evenly. It shields the signal in certain directions and
causes distorted radiation lobes. QMS gains another 3
to 6 dB.
• An antenna coupler mounted in the trunk of a vehicle will
have 1 to 2 feet of HV cable going to the antenna on
the outside. A lead wire as short as 1-foot, with a 9-
foot antenna, means that fully 10% of the antenna sys-
tem is inside the vehicle where it will neither transmit
nor receive. It also creates another 10 to 100 pico
Farads of capacitance which results in more losses.
With QMS, you’ll pick up 3 to 6 dB.
• Wire size of the antenna counts. Most resonant type anten-
nas are wound with number 22 wire. The SG-303, the
antenna used with the QMS, is wound with 3 millime-
ter wide tape wire strap—equivalent to AWG #4 wire.
With a 100-watt transceiver, you’ll develop 3 to 7
amps (or more) of RF on the antenna, and 7 amps
through #22 wire represents major losses. The QMS
with the SG-303 antenna scores another 3 to 6 dB
advantage.
• The SG-303 is actually two antennas in a single casing. A
single rod equivalent to the conventional stainless
steel whip element resonates at about 22 MHz; in addi-
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© 1997 SGC Inc.
SGC Inc. SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA
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