The National Bureau of Standards is a principal focal point in the Fvderal Government for assuring maximum application of Iti. physical and enpinveriina sciences it) the ad~ziiienient oif technology ill iodustr% anid commerivrce. Its responsibilities include development and mainteniaic oif the niational simolar(Is idf measurement, and the provisions of means for making measuremnrirts conskistet %ith tbose slannda rds; determination of t~aical constants arid properties of materials: ditviclopirnt it(o methiods for te-ting materials, rncchari. s, and soructures. and making such tests it-; may be riccessarv, parlicti. larlv for gove-rnrnent agencies; cooperation in (lie establishment of standard piactices for incorpora. lion in codes and specifications; advisory servire to} government ag~encies on scientific tod itechinial prolemsn: inivenrtion and development of devices to serve special needs of fay Laboratory Abtmophy-irs at the Vniver-ity ,I Col.,ratr locaird at ltoulder, h.. 1
During 1959 a nd 1960 long-term tra nsmissio n loss measurem ents were p erform ed over a 223 kilom eter path in Eastern Colorado using fr equencies of 100 a nd 751 megacycles per second. This pat h i ntersects P ikes P eak which form s a kn ife-edge ty pe obstacle visible from both term inals. The transmissio n loss measurements have been analyzed in te rms of diurnal a nd seaso na l va riations in hourly m edians and in in stan taneous levels. As expected , results s h ow t hat the long-term fa di ng range is s ubstantially less t ha n expected for t ro pospheric seatter paths o f comparable length. T rans miss ion loss levels were in general agreem ent wi t h predicted k ni fe-edge d iffraction propagation whe n a ll owance is made for rounding of t he knife edge. A tec hnique for est imatin g long-term fading ra nges is p rese nted a nd t he res ults are in good ag reeme nt with obse rvat ions. Short-term variations in so me case resembl e t he s pace-wave fad eo uts commo nly obse r ved o n within-t he-horizon paths, a ltho ugh other phenomena may contribu te to t he fad in g. Since t he foreground te lTa in was rough there was no evidence of direct a nd grou nd-refl ected lobe structure. ' In most cases comparative ly 1 1igh co rrelation exists bct\\'ec ll signals received simultaneously on t wo a nte nn as with 8.3 an d 14 m eters ver t ical se paration. These se parations were chosen as being represe ntative fo r practical s pace d ive rsity systcms desig ned for eli minating t he eff ects of fading a ri sin g from direct and grou nd-rcf1ected phasc inter Fere ncc phc nom e na. The co mparatively hi gh co rrelatio n obse rved suggests t hat s pace diversity wi ll be re lativcly less successfu l in mountain obstac le paths with rou g h terrai n ncar t he ter min a ls than on t roposphe ri e seatter paths or on line-of-s ight paths over s mootll terrain. The enha ncement of fi eld strength associated with propagatioll over mountain ridges ITIay causc concern ill applicatio ns where Illountain are being co unted o n to hi elel uJlwantod radio waves. Somc rad io a stro nomy installations have bec n locateel in llloullLain vall eys fOf t his reaso n, and it is possible that obstacle-gai ll eii'ects ma.\" agg ravatc rather t ha n a ll e viaLe Interfe renc e.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.