. The Bell System Technical Journal . m Antennen auf dem Dach des Long LinesBuilding, 32 Avenue of the Americas, New York City. Diese Antennen wxre 450 Meter über dem Boden. Einer der vorhandenen Mobile Service-Transmitter diente für die 150-mc-Tests. Für die Tests 450, 900 und 3700-mc wurden spezielle experimentelle Transmitter eingerichtet. Alle waren in der Lage, die Frequenzmodulation. Die mobile Einheit war ein Kombi, der mit den verschiedenen Frequenzen Signale empfangen und messen konnte. Die Empfangsgeräte wurden für eine schnelle Umstellung von 150 auf 450 auf 900 mc eingesetzt. Die Bandbreite (ca. 50 kc) und das System
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. The Bell System technical journal . m antennas on the roof of the Long LinesBuilding, 32 Avenue of the Americas, New York City. These antennaswxre 450 feet above ground. One of the existing Mobile Service trans-mitters served for the 150-mc tests. Special experimental transmitterswere set up for the 450, 900, and 3700-mc tests. All were capable offrequency modulation. The mobile unit was a station wagon equipped to receive and measur-signals at the various frequencies. The receiving equipment was ar-ranged for rapid conversion from 150 to 450 to 900 mc. The bandwidth(about 50 kc) and system modulation (±10 kc) were identi(;al at allthree freciuencies (equal to the existing standards at 150 mc). The 3700-mc tests were handled separately. It was not possible to employ thesame bandwidth and deviation, but this does not invalidate the com-parison of signal propagation at the Aarious frequencies. A most useful tool in making these measurements was a device knownas a Level Distribution Recorder, or simply LDR. This was built. miomo CD lO a, ■ 1074 MOBILE RADIO TRANSMISSION 1075 especially for these tests and is similar to its foieninners which havebeen used in the past for measuring- atmospheric static noise. Tlie LDR, in combination with a caliliiated radio r(Meiver, is capable of taking asmany as twenty instantaneous sami)les of radio sij>;nal str(Mif>;th per sec-ond, sorting the samples by amplitude, and rendering infoiination on abatch of samples from which a statistical distribution (•ure can beplotted. The LDR was also us(xl for measuiing the statistical distributionof audio noise in the output of the radio receiver. The LDR was, in thiscase, associated with a special con-erter whose characteristics resemblethose of a 2B noise measuring set. No arrangements were made for measuring radio proi)agation frommobile unit to a land receiver. It was felt that the comparison by fre-quencies woidd be substantially the same as in the outward directionof transmiss
