Practical_Antenna_Handbook_0071639586

C h a p t e r 1 5 : H i d d e n a n d L i m i t e d - S p a c e A n t e n n a s 369
House, tree or
other structure
Insulator
Rope
/4 radiator /4 radiator
Center insulator
Coax
Insulator
Rope
Ground
Figure 15.4A Sloping dipole.
thus allowing the use of coaxial cable for the feedline and potentially eliminating the
need for an ATU. In contrast to center-fed dipoles, this antenna is a sloping monopole
that is strongly dependent upon a good RF ground at the feedpoint for reasonable
transmit efficiency.
Figure 15.5 shows another antenna that’s useful for limited-space situations. Although
it is easily constructed from low-cost materials, the antenna is also sold by several
companies under various rubrics including “cliff-dweller”, “apartment house”,
“town house”, or “traveler’s” antenna. It consists of a 4- to 16-ft section of aluminum or
copper tubing. Some of the commercial antennas use telescoping tubing that can be carried
easily in luggage. As with the longwire, this windowsill antenna is tuned to resonance
with an L-section coupler. Again, a good ground (or radial system) will greatly
improve the performance of this antenna, which is capable of working DX for you—
even on the lower frequencies.
Figure 15.6 shows the use of a mobile antenna for a fixed or portable location. Simply
mount a mobile whip, such as the Hustler, on the windowsill or other convenient
mount. Since this, too, is a vertical monopole, an adequate ground system is essential to