Specifications

SMARTUNER MANUAL 51
SGC Inc. SGC Building, 13737 S.E. 26th St. Bellevue, WA. 98005 USA
© Nov2000 SGC, Inc. P.O. Box 3526, 98009 Fax: [phone] Tel: [phone]
E-Mail: [e-mail] Web Site: www.sgcworld.com
Wire running parallel to a grounded surface may represent a significant capacitance to
ground and, just as with coax, this will cause problems.
To give you an idea how these two points can cause problems, let us relate an incident
that happened in late 1992. A SMARTUNER user had a coupler installed in a mobile
ham radio installation. The coupler could not find a lock on several bands. After going
through his installation carefully, the user called SGC for technical support. This user
was nearing wit’s end.
In working through the logical troubleshooting process with him, we discovered that he
had used coaxial feed line from the insulator on the coupler to the antenna feed point.
Because he had read about the dangers of capacitance to ground in an earlier edition of
this manual, he did not have the coax shield grounded. We had him remove the
ungrounded braid and the installation worked fine.
Experiences like this have taught us to be fanatical about using the shortest possible
wire and no coax on the output of the coupler.
Another key lesson here is that even if you have a low capacitance lead, a high
capacitance antenna will not work well. If you have a whip type antenna, mounted on
the back of a van, you will have a large portion of the antenna running right next to
grounded sheet metal. This causes a high loss to ground, one reason why we do not
recommend CB type whip antennas. The other reason is the base insulation in ball
mounts is inadequate for everything but extremely low power.
Long lead lines. If you have a SMARTUNER feeding a 9-foot antenna with a 1-foot feed
line located inside a hull or inside a vehicle, you have 10% of the antenna where it will
do you no good. If you have more than 5% of the antenna inside a grounded cabin, you
will begin to lose performance.
A good rule of thumb is that under one foot of feed line is a good installation, one to
two feet aren't very good installations, and over two feet means you are asking for
trouble.
“Odd reactance.” The next category of antenna fault is what we call the “odd reactance”
problem. Although the SMARTUNER is an exceptionally well-designed product, you
may from time to time find an antenna length that just won’t quite work right.
Generally this occurs when the SMARTUNER is having a tough time making up its
mind about which of two tuning solutions is better. If it is a very close call, you can
have an antenna which causes cycling and just won't stay locked.
The solution in such cases is to add or subtract a couple of feet of wire from the antenna.
This generally cures the problem.