TWIN-LEAD J-POLE VHF ANTENNA

TWIN-LEAD J-POLE VHF ANTENNA
TWIN-LEAD J-POLE VHF ANTENNA
This is a design from an article by W9VZR in 73 Magazine ©, August 1977, P. 60
TV antenna 300 Ohm plastic twin-lead ribbon cable is cut to make a 50 Ohm VHF portable antenna
RADIATOR, 1/2 Wave
A
300 Ohm Plastic Twin<— NO CONNECTION, CUT AND REMOVE TO END —>
B
STUB, 1/4 Wave
50 Ohm Coaxial Cable
To A
To B
FREQUENCY (MHz)
28.0
28.5
29.0
50.0
RADIATOR (Inches)
197.8 194.3 191.0 110.8 108.6 106.5 38.4 38.2 37.9 37.7
STUB (Inches)
102.8 101.0 99.3
57.6
51.0
56.4
52.0
55.3
144
145
20.0 19.8
146
147
19.7 19.6
Note that the upper end of the stub is simply cut and does not connect to anything. The lower
end of the stub connects to the coaxial cable’s shield braid. Cut and strip away the excess
plastic and the wire from the point where the stub is cut to the tip of the twin-lead.
The twin-lead “J” antenna can be cut for any frequency from about 26-500 MHz. The formula
is shown below:
Radiator (in inches) =
5540
Freq. in MHz
Stub (in inches) =
2880
Freq. in MHz
The total length of twin-lead needed is the radiator length + the stub length.
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