6
CHECKOUT AND ADJUSTMENT
ground system used, greater bandwidth being associated with lossy ground systems. It should be
remembered that on those bands where the physical height of a vertical antenna is less than a quarter
wavelength, the earth (or the resonant radial system in above-ground installations) will have a good deal
to do with VSWR, antenna tuning, bandwidth, and overall performance.
Low VSWR by itself does not mean that a vertical antenna is operating efficiently, and if low VSWR is
obtained with no more than the usual "quick and dirty" ground connection, it most likely means the
opposite. In general, poor operation or improper tuning of vertical antennas can usually be traced to
inadequate (or even reactive) ground systems or to other vertical conductors in the vicinity of the
antenna. For these reasons it is suggested that the antenna be placed as much in the clear as possible and
used with the best ground system that conditions permit. For a more complete discussion of the inter-
relationships between vertical antenna efficiency, bandwidth, VSWR etc., a standard text such as the
A.R.R.L. Antenna Book is recommended. Also review the material included at the end of these
instructions.
For adjustment purposes a simple VSWR indicator may be used. More accurate measurements may be
made at the antenna, i.e. at the junction of the 75 ohm matching line and the main transmission line, but
the tuning conditions that exist at the transmitter will usually be of greater interest.
1. Determine the frequency at which VSWR is lowest on 80/75 meters. The coil settings given earlier
should produce resonance and lowest VSWR at approximately 3700 kHz. To raise the frequency of
resonance and lowest VSWR, simply loosen the wing nut on the lower coil clamp of the lower (80
meter) coil on section B and stretch the coil a bit more. To lower the frequency, compress this coil.
A one inch change in the setting of this coil will produce a frequency shift of approximately 125 kHz.
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. It would be wise to take
VSWR readings every 25 kHz or so to avoid "running past" the frequency of resonance and lowest
VSWR. To minimize interference to other stations and to avoid erroneous readings, use only enough
power to produce full scale deflection of the meter in the "forward" or "R.F. out" position.
Once the proper coil setting has been found for the desired band segment, coil Q base matching (Q)
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 (Q) is left fully compressed, if earth
losses are low as with an extensive radial system, coil Q base matching (Q) 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 (Q) should suffice for operation over most of
80/75 meters provided the 80 meter coil is readjusted for each different band segment.
2. 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 settings of
the upper coil clamp of the 40 meter coil. On this band the setting is much less critical and a one
inch change in the clamp setting will shift the VSWR curve approximately 80 kHz. Be sure to loosen
the clamp around tube (B3) that supports the 30 meter assembly and to reposition it as needed to
avoid distorting the 40 meter coil.
3. Check VSWR on 20 meters. Tuning is quite broad on this band because the antenna is physically
much taller than a quarter wavelength. To raise the frequency of lowest VSWR, reposition the 30
meter assembly so that the L clamp can be replaced on the next lower turn of the 40 meter coil, refer
to step 27 in the assembly instructions. Alternatively, to lower the frequency of lowest SWR,
reconnect the L clamp 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 to permit adjustments of less than one full turn.
4. Check VSWR on 15 meters. The VSWR curve may be shifted upward or downward by changing the
