Technical information

tion, a helically wound element resonates at about 10
MHz. This means that on lower frequencies, those under
20 MHz or so, the SG-303 will vastly outperform a con-
ventional 9-foot whip.
• Some hams use the “antenna tuner” built into some radios,
feeding their antennas directly with coax. But in a non-
resonant antenna, a very high SWR exists on the feed-
line between the radio and antenna even if you get a
low SWR reading with a built in tuner. When your feed-
line SWR is above 4 to 1, you have effectively put 29
pico Farads per foot capacitance to ground. Whereas
built-in tuners are merely trimmers, the QMS system-
puts a true coupler right at the antenna, adding at least
3 to 6 dB more gain for QMS.
No holes in mounting. QMS mounts without drilling any
holes in your vehicle, a major advantage at vehicle trade-in
time. (See Chapter 6 and Appendix A for installing the QMS
system.)
Mobile Grounds
“They don’t build ‘em like they used to” is certainly true
about today’s automobiles. Not only do they have more
wires—which can pick up stray RF—but they generally have
fewer welds—which means the ground system presented by
the vehicle may not have high integrity. As a result of a
smaller ground system, ground loops may occur, and in some
situations, reduced radiation efficiency.
Here are some guidelines that will eliminate some ground
issues:
Wire runs. Keep all wire runs as short and direct as possi-
ble. This means keeping the path direct. It is especially
important to keep the antenna wire from the SG-235 coupler
as short as possible to the external mobile antenna (we rec-
ommend the SG-303).
20
SGC Inc. SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA
P.O.Box 3526, 98009 Fax: [phone] or 746-7173 Tel: [phone] or 1-800-259 7331
E-mail: [e-mail] Website: http://www.sgcworld.com
© 1997 SGC Inc.