-10-
CHECKOUT AND ADJUSTMENT
10. Check VSWR on 6 meters. To raise the frequency of the lowest VSWR,
shorten the length of the wire and to lower frequency increase the wire
length. Alternatively, the upper clamp and the entire 6 meter assembly may
be placed higher on the antenna to lower frequency or lower to raise it.
11. Adjustments for 40, 30, 20, 15, 17, 12, 10 and 6 meters should have little or
no effect on the previous adjustments for 80/75 meters, but a final VSWR
check for this band should be made as in step 1 above.
NOTE: In above-ground installations it will usually be found that
resonance and lowest VSWR occur at slightly higher frequencies
on all bands compared to ground-level installations. Therefore on
15 and 10 meters, where length adjustment is the means of
getting antenna resonance, it is recommended that the length of
the stranded-wire between wire clamp 0.500" 15 M w/wire (L)
and wire clamp 0.875" 15 M w/insulator (K) be increased
approximately 3 in (7.6 cm.) and that tube (J) be extended
approximately 6 in (15.2 cm.) beyond the original dimensions
given if any above-ground installation is contemplated. These are
merely recommended preliminary settings, for it is impossible to
indicate precise settings that will produce resonance or lowest
VSWR at a given frequency in all installations.
In the preceding steps it has been assumed that the antenna has been installed in
a more or less clear spot away from other vertical conductors such as TV antenna
feedlines, towers and masts, and that a minimal ground system (or a system of
resonant radials in the case of above-ground installations) has been installed.
If those fairly basic conditions have not been met it is likely that resonance and
low VSWR will be impossible on some or even all bands. One should bear in mind
that VSWR, even with a resonant antenna, will depend in large measure on local
ground conductivity, height above ground in the case of an elevated antenna, the
extent of the radial, counterpoise or other ground system used, and on other
factors over which the operator may have little or no control. Fortunately, the
evils of VSWR greater than unity have been grossly exaggerated in recent
decades, and the only practical difference between a VSWR of unity and one of,
say, 3:1 in the average case lies in the reluctance of modern equipment to deliver
full power into lines operating at the higher VSWR without the help of a
transmatch or other outboard matching device. Transmitters having so-called
broadband solid-state output circuits (no tuning or loading controls) may be
especially troublesome in this regard, whereas the older vacuum tube pi-network
transmitters can usually be adjusted for maximum output over a tuning range
where the VSWR does not exceed 2:l.
