. The Bell System technical journal . ctric vector in three mutually perpendicular co-ordinates are givenby Norton. In addition to the effect of the earth on the propagation of radio waves,the presence of the ground may also affect the impedance of low antennasand thereby may have an effect on the generation and reception of ^ As the antenna height \aries, the impedance oscillates aroundthe free space value, but the variations in impedance are usually unim-portant as long as the center of the antenna is more than a quarter-wavelength above the ground. For vertical grounded antennas
. The Bell System technical journal . ctric vector in three mutually perpendicular co-ordinates are givenby Norton. In addition to the effect of the earth on the propagation of radio waves,the presence of the ground may also affect the impedance of low antennasand thereby may have an effect on the generation and reception of ^ As the antenna height \aries, the impedance oscillates aroundthe free space value, but the variations in impedance are usually unim-portant as long as the center of the antenna is more than a quarter-wavelength above the ground. For vertical grounded antennas (such asare used in standard AM broadcasting) the impedance is doubled and thenet effect is that the maximum field intensity is 3 db above the free spacevalue instead of 6 db as indicated in (4) for ele\ated antennas. Typical \alues of the field intensity to be expected from a groundedquarter-wave vertical antenna are shown in Fig. 12 for transmission overpoor soil and in Fig. 13 for transmission over sea water. These charts in- 120. 4 6 8 10 20 40 60 100 200 400 600 1000 DISTANCE IN MILES Fig. 12 — Field intensity for vertical polarization over poor soil for 1-kwradiated power from a grounded whip antenna. 120 100 1^ 80 H| 60 O> oq: u 2 40 i 20< in _i111 U 0 -20 -40 ^ S X :^ ^ ^ ^?=^ s s V \ k \ \ S sT^^ V ^ ^ s \ \ \ \ k ^^^^ tN. 1^ -, S. •v s \ ^ N s. ^\^ SV sWV - , >^ \ \ V \, \, > . \ \ S^ i\ ^ \ \ s ,\ \ \ \ \ \ v^ li iK \. \ ^ s. s. V 15\ \ ^ kW V s, \, \, \ 30\ \ \ \\ kS\ \ V X \ 60\ \ \ \ \\ k \ ^ S. 15(X \ \ \ \ \ k\ \ \303X \ \ \ V , \ \ * k\^ 600\ \ V \ \ \ \ > , \ — MC N V^ H \ ^ \ -^ \ -\ \ ^ 1 1 1 1 1 1 A 1 ^ \ V rt L 1 \ \ \ \ 1 4 6 8 10 20 40 60 80100 200 400 600 1000 DISTANCE IN MILES Fig. 13 — Field intensity for vertical polarization over sea water for 1-kwradiated power from a grounded whip antenna. 616 RADIO PROPAGATION FUNDAMENTALS 617 elude the effect of diffraction and average refraction around a s
Size: 1782px × 1402px
Photo credit: © Reading Room 2020 / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
