AS-40 Trap Dipole
Antenna Kit
Internet Instruction
Sheet
The Barker & Williamson Model AS-40 is a short dipole for the 40,
20, 15 and 10 meter amateur bands. Each band has a separate trap (20, 15 and 10
meters) which will give maximum efficiency and still be a short antenna for
small lots and limited space. On 15 meters the 10 meter traps work as loading
coils, and on 20 meters both the 10 and 15 meter traps work as loading coils
keeping the antenna short for 20 meter operation. On 40 meters all the traps
work as loading coils keeping the antenna short for 40 meters. All short dipole
antennas will have a bandwidth narrower than a full size half wave dipole.
Therefore, an antenna tuner may be helpful.
The AS-40 is best installed as an inverted Vee. Satisfactory results may be
obtained with the center as low as 20 feet, however 30 feet or more is
recommended. If a flat top installation is desired, it is best to have the
center supported due to the weight of the traps/loading coils and coaxial feed
line.
INSTALLATION INSTRUCTIONS
(1) Please read through all the instructions before starting. It is
imperative to follow the instructions step by step, in the order shown, to
achieve satisfactory results with your antenna.
(2) Remember that throughout the assembly procedure, wire lengths are always
to be symmetrical on both sides of the antenna. Your traps may or may not have a
color dot on one end of them. You may ignore these color dots. They do not have
to match each side.
(3) Cut the wire segments. The wires must be cut approximately 2 - 3 feet
longer than the dimensions shown in figure 1. This is to leave room for the
hookups and tuning adjustments. Here are the lengths that you should cut
(including the 2 - 3 ft extra). Cut four wires 11', two wires 4', and two wires
3'. Remember, you can always trim the wire shorter after tuning, but once cut
too short . . .
(4) Attach one end of the wire segments in the permanent manner shown in
figure 2, working out from the center conductor. Allow roughly 6 to 8" of wire
through the eyebolt before starting your wrap. Attach two of the 11' segments to
both sides of the center connector. Attach the 3' segments to one side of the
TR10 traps. Attach the 4' segments to one side of the TR15 traps. Attach the
other two 11' segments to one side of the TR20A traps.
(5) Now assemble the sections of the antenna together paying attention to
figures 1 and 3. The wire segment lengths shown are your starting point for
tuning the antenna. Make sure that you make temporary connections as shown in
figure 3. This will leave each wire segment with one end permanently soldered,
and the other end temporarily connected for adjustment.
(6) Raise your antenna, and check the VSWR on 10 meters. If the resonant
frequency is low, shorten the inner 8' 5" segments (attached to the center
connector). If it is high, lengthen the wires. After the desired frequency is
achieved, make permanent attachment for these segments as shown in figure 2,
trimming off excess wire.
(7) Next adjust the 13" segments for 15 meters in the same manner.
(8) Next adjust the 21" segments for 20 meters in the same manner.
(9) Finally, adjust the outer 8' 5" segments at the insulators for 40 meter
operation.
Figure 1: Theoretical wire lengths and trap arrangement (half antenna
shown):
SWR curves:
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