SG-2000 MANUAL
45
The SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA
©1995, SGC, Inc.
TEL: (206) 746-6310 FAX: (206) 746-6384
not generally well built and may fail when used in commercial service because of its
poor base insulation and its lack of a shock absorbing base. It just whips around and
doesn't stay where it belongs.
Single element commercial heavy duty antennas such as those made by Hustler are a
step in the right direction for lower frequency HF work. Although some companies still
sell 108" stainless steel whip-based products, the professional HF person will always
choose a center or top loaded whip antenna if a single frequency is to be used.
When a series of frequencies spread across the spectrum is to be used, the professional
answer is either to put up with changing loading coils or to put in a continuously
loaded helically-wound antenna. This provides a reasonable load to a good antenna
coupler at all frequencies from about 1.8 to 30 MHz.
SGC is the only manufacturer to add the good attributes of a 108" whip (which
performs well at the 20 MHz range and above) with the high performance of a helical
antenna that performs well at the lower frequencies.
The use of an antenna coupler is required on all but the most carefully matched center-
and top-loaded mobile whip antennas which present close to a 50 ohm match to the
antenna lead.
Although it is tempting to use both a coupler and a center loaded antenna, the center
loading element of a loaded antenna already acts as an RF choke at high frequencies.
Thus, it actually reduces the effective length of an antenna if used on a high band.
11.7
QMS Recommended for Mobile Use
SGC engineers have discovered that the QMS-II antenna system, comprising an SGC
coupler (the SG-230 Smartuner™ or the two new couplers — the SG-230 Smartuner™
Pro and the SG-235) mounted in a QMS and driving the SG-303 high performance whip
antenna will typically yield substantial improvement in gain over a conventional 1.8 to
30 MHz HF mobile antenna installation. When we start making claims of 20 dB, a lot of
people (maybe even you) will be skeptical. So let us show you how you can get a
significant increase in gain by simply using a QMS compared with any other 1.8 to 30
MHz system:
1.
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 bod
y
sheet metal
. This is equivalent to a capacitor of 25 to 100 pico Farads
shorting your antenna. QMS, mounted high on the side of the vehicle, gains 3 to 6
dB.
2.
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.