. The Bell System technical journal . cl,^d, ANT2 \ -50 -30-20\ l-io \ h5\l 5000- 2000-1000- ^ 500- tilLUu- 200 • -3-2 * 100-50- 20-10- - 10,000 - 5000 3000-2000 -1000 - 500 *-^^ 1-III - 300-200 z \100 \ I - 50 \ 30 \-20 ^ 10 |- 5 3 - 2 - 1 ■^ note: when accuracy greater than± db is required, values onthe d, scale should be: 30-60- 150-300-600 1500H3000 76 000- 1 5,000 ,000- Ozou LU a. UJQ. CO LU _l ue) LU 2 U. o LU _l 111> I-< UJ I/) 0- UJ z^ iH / 0 - •10 I 1-12 7\A -16-18-20 Oa. 2b en _i LU m ■30 \l,a z■35 ^ O -40 -45 - 50 d2 Fig. 7 — Knife-edge diffrac
. The Bell System technical journal . cl,^d, ANT2 \ -50 -30-20\ l-io \ h5\l 5000- 2000-1000- ^ 500- tilLUu- 200 • -3-2 * 100-50- 20-10- - 10,000 - 5000 3000-2000 -1000 - 500 *-^^ 1-III - 300-200 z \100 \ I - 50 \ 30 \-20 ^ 10 |- 5 3 - 2 - 1 ■^ note: when accuracy greater than± db is required, values onthe d, scale should be: 30-60- 150-300-600 1500H3000 76 000- 1 5,000 ,000- Ozou LU a. UJQ. CO LU _l ue) LU 2 U. o LU _l 111> I-< UJ I/) 0- UJ z^ iH / 0 - •10 I 1-12 7\A -16-18-20 Oa. 2b en _i LU m ■30 \l,a z■35 ^ O -40 -45 - 50 d2 Fig. 7 — Knife-edge diffraction loss relative to free space. 608 THE BELL SYSTEM TECHNICAL JOURNAL, MAY 1957 LUO< fflO UJ o. FIRST FRESNEL ZONE Fig. 8 — Transmission loss versus clearance. At grazing incidence, the expected loss over a ridge is 6 db (Fig. 7)while over a smooth spherical earth Fig. 6 indicates a loss of about 20db. More accurate results in the vicinity of the horizon can be obtainedby expressing radio transmission in terms of path clearance measuredin Fresnel zones as shown in Fig. 8. In this representation the planeearth theory and the ridge diffraction can be represented by single lines;but the smooth sphere theory requires a family of curves with a param-eter M that depends primarily on antenna heights and frequency. Thebig difference in the losses predicted by diffraction around a perfectsphere and by diffraction over a knife edge indicates that diffractionlosses depend critically on the assumed type of profile. A suitable solu-tion for the intermediate problem of diffraction over a rough earth hasnot yet been obtained. Experimental Data Far Beyond the Horizon Most of the experimen
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Keywords: ., bookcentury1900, bookdecade1920, booksubjecttechnology, bookyear1
