Circuit Diagram
Description
Wound on a 3 foot length of PVC pipe, the long loopstick antenna was
an experiment to try to improve AM radio reception without using a long
wire or ground. It works fairly well and greatly improved reception of a
weak station 130 miles away. A longer rod antenna will probably work
better if space allows. The number of turns of wire needed for the
loopstick can be worked out from the single layer, air core inductance
formula:
Inductance = (radius^2 * turns^2) / ((9*radius)+(10*length))
where dimensions are in inches and inductance is in microhenrys. The
inductance should be about 230 microhenrys to operate with a standard AM
radio tuning capacitor (33-330 pF). The 3 foot PVC pipe is wound with
approximately 500 evenly spaced turns of #24 copper wire which forms an
inductor of about 170 microhenrys, but I ended up with a little more
(213uH) because the winding spacing wasn't exactly even. A secondary
coil of about 50 turns is wound along the length of the pipe on top of
the primary and then connected to 4 turns of wire wound directly around
the radio. The windings around the radio are orientated so that the
radio's internal antenna rod passes through the external windings. A
better method of coupling would be to wind a few turns directly around
the internal rod antenna inside the radio itself, but you would have to
open the radio to do that. In operation, the antenna should be
horizontal to the ground and at right angles to the direction of the
radio station of interest. Tune the radio to a weak station so you can
hear a definite amount of noise, and then tune the antenna capacitor and
rotate the antenna for the best response. The antenna should also be
located away from lamp dimmers, computer monitors and other devices that
cause electrical interference.
Post a Comment