The VHF/UHF spectrum is commonly acce[ted to range from 30 MHZ to 900 MHZ,
although the upper breakpoint is open to some differences of opinion. The VHF
spectrum is 30 MHz to 300 MHz, and the UHF spectrum is 300 MHz to 900 MHz.
Above 900 MHz is the microwave spectrum.
The concept “VHF/UHF antenna” is only partially valid because virtually all forms
of antenna can be used at HF, MW, and VHF/UHF. The main limitations that distinguish
supposedly VHF/UHF designs from others are mechanical: there are some
things that are simply much easier to accomplish with small antennas.
Wavelengths for these bands range from 10 m to 1 m for the VHF region, and
from 1 m to 33 cm for the UHF region. Most antenna designs are based on wavelength,
so that fact has some implications for VHF/UHF antenna design. For example, because
bandwidth is a function of length/diameter ratio for many classes of antenna,
broadbanding an antenna in the VHF/UHF region is relatively easy. If, say, 25-mm
(i.e., 1-in) aluminum tubing is used to make a quarter-wavelength vertical, then the
approximate L/D ratio is 790 in the 8-m band and 20 in the 2-m band. This feature is
fortunate, because the VHF/UHF bands tend to be wider than the HF bands.
Another point to make is that many of the mechanical chores of antenna design
and construction become easier for VHF/UHF antennas. One good example is the
delta impedance-matching scheme. At 80 m, the delta-match dimensions are approximately
36 - 43 ft, and at 2 m they are 9.5 - 12 inches. Clearly, delta matching
is a bit more practical for most users at VHF than at HF.