Dept. il 4844 W. fullerton Ave.
Chicago, ill. 60639
Frank Jones WÓAJF-AF6AJF 850 Donner Avenue Sonoma, California
Loiv noise, inexpensive, easy-to-bnild converters and filter for our highest VHF hand
The 220 to 225 mc band in many locations is subject to strong image signal problems which can be reduced greatly by using a pair of high Q circuits in the antenna feeder. An antenna filter of this type suitable for transmití irig and receiving service is shown in Fig, 1. It consists of two high Q circuits capacity coupled together at the tuning end of each line and loaded down to a working Q of about 25 for 50 ohm coaxial input and output lines. This loading is chosen by the position of the coax jack taps on each iiat plate line near its grounded end, A tap point 1>5 inches from ground end seemed to function well over a large portion of the 220 mc band. The circuits are tuned to resonance by spring brass p:ates with adjustable spacing to the flat plate ¡¡ne at the "hot" end. The coupling capacitor is at this end also and consists of an insulated U shaped metal bracket as shown in Fig. 1, f'he coupling depends upon the spacing at I he ends so some adjustment can be made by bending the sides oi the U bracket or by making a new one with more or less length between the sides of the U. Probably a better coupling scheme would be an aperture cou-
cl s cl are spring ej^ass-pl at es 3-1/2" * m/2'' with 1/2" lip fop mounting^
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