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Alternatively, to lower the frequency of lowest SWR, reconnect the coil support tube 30 meter L
bracket (O1) to the next higher turn of the 40 meter coil.
In some cases moving the tap point a full turn up or down may cause more of a frequency shift
than is desired, in which case the entire 30 meter assembly may be rotated around tube (E) to
permit adjustments of less than one full turn.
7. Check VSWR on 30 meters. To raise frequency, loosen the wing nut on the bottom coil clamp
of coil/capacitor assembly 30 meter (P), stretch the coil and retighten the wing nut.
To lower frequency, compress the coil.
A change of only 1/4 inch will shift the VSWR curve approximately 100 kHz. Large changes in
the setting of coil/capacitor assembly 30 meter (P) may affect 20 and 40 meter tuning, in which
case it may be necessary to repeat steps 3 and 4. In general, the point at which the 30 meter coil
taps on to the 40 meter coil will be the major factor in 20 meter tuning.
8. Adjustments for 40, 30, 20, 15 and 10 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
described earlier.
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" 15M with wire (L)
and wire clamp 0.875" 15M with insulator (K) be increased approximately 3 inches and that tube (J)
be extended approximately 6 inches 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.
