Practical_Antenna_Handbook_0071639586

C h a p t e r 1 6 : M o b i l e a n d M a r i n e A n t e n n a s 387
The tuner can be any of several designs, shown in Fig. 16.7. The reversed L-section
coupler shown in Fig. 16.7A is used when the antenna radiator element length is less
than a quarter-wavelength. Similarly, when the antenna is greater than a quarter-Â
wavelength, the circuit of Fig. 16.7B is the tuner of choice. This circuit is a modified
L-section coupler that uses two variable capacitors and an inductor.
Finally, we see in Fig. 16.7C the coupler used on many radios for random-length
antennas. Two variable inductors are used: L 1 resonates the antenna, and L 2 matches the
feedpoint impedance to the characteristic impedance of the transmission line. In some
A
B
4
4
L 1
C
C 1
C 2
L 2
Figure 16.7 Antenna tuners for broad HF antennas.
L 1
28 H