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To lower frequency, feed more of the
tail
back through the hole in the insulator to increase the
length of the wire between wire clamp 0.500" 15M with wire (L) and wire clamp 0.875" 15M
with insulator (K). A change of 2 inches will shift the VSWR curve approximately 300 kHz.
3. Determine the frequency at which VSWR is lowest on 80/75 meters. The coil setting given
earlier should produce resonance and lowest VSWR at approximately 3700 kHz.
To raise the frequency of resonance of the lowest VSWR, simply loosen the wing nut on the
lower coil clamp of the coil assembly 80/40 meter (C) coil on tube (B) and stretch the coil a bit
more.
To lower the frequency, compress the coil. A One inch change in the setting of this coil will
produce a frequency shift of approximately 125 kHz.
NOTE:
Remember that the antenna tunes very sharply in this range and that high values of VSWR
may be encountered only a few kHz either side of the lowest VSWR readings, so it would be
well to take VSWR readings every 25 kHz or so to avoid
running past
the frequency of
resonance and lowest VSWR.
NOTE:
To minimize interference to other stations and to avoid erroneous reading use only enough
power to produce full-scale deflection of the meter in the
forward
or
R.F. out
position.
4. Once the proper coil setting has been found for the desired band segment, coil (Q) base
matching at the base of the antenna may be adjusted for even lower VSWR. If earth losses are
moderate to high a good match may be possible if coil (Q) base matching is left fully
compressed; if earth losses are low (as with an extensive radial system) coil (Q) base matching
may have to be stretched to twice its compressed length or more for a good match. In any case, a
single setting for coil (Q) base matching should suffice for operation over most of 80/75 meters
provided the 80 meter coil is readjusted for each different band segment. Note that coil Q will
have to be cut to remove turns and stretch the coil. The combination of cutting and stretching
should be such to keep the dimensions of the coil reasonable and strong mechanically. Most
installations will have to stretch and remove turns considerably. As you make the adjustments,
check your VSWR, note that you CAN, and should get it down to 1:1.
5. Determine the frequency of minimum VSWR on 40 meters. The coil setting given earlier should
produce resonance and lowest VSWR at approximately 7150 kHz. The 40 meter VSWR and
resonance curve may be shifted in the same manner as on 80/75 meters by changing the setting
of the upper coil clamp of coil assembly 80/40 meter. On this band the setting is much less
critical, and a 1 inch change in the clamp setting will shift the VSWR curve approximately 80
kHz. Be sure to loosen the clamp around tube (E) that supports the 30 meter assembly and to
reposition it as needed to avoid distorting the 40 meter coil.
6. Check VSWR on 20 meters. Tuning is quite broad on this band because the antenna is
physically much taller than a 1/4-wavelength.
To raise the frequency of the lowest VSWR, reposition the 30 meter assembly so that the coil
support tube 30 meter L bracket (O1) can be replaced on the next lower turn of the 40 meter
coil.
