The Roswell Report: Fact vs. Fiction in the New Mexico Desert

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## B. Transmitters Used

## (1) 72-Megacycle Radiosonde Transmitter (T-49)

The standard T-49 transmitter of the Army Weather Service was first used in project work, with a modified commutator bar switching specially coded resistors into the circuit as the balloon passed from one critical pressure to another. The operating characteristics of this transmitter may be found in the following publications: T.B. Sig. 165, T.M. 11-2403, T.M. 11-2404 and the Weather Equipment Technician's Manual.

The defects which were encountered in the use of this transmitter were principally (1) relatively short range and (2) unfitness for direction-finding using available equipment. Our experience has been that reception from the T-49 transmitter by standard equipment is not much above 80 miles under good conditions. When flights were made which traveled many times this distances, the inadequacy of this transmitter was clearly demonstrated.

The problem of direction-finding is of major importance when attempts are made to position and track the balloon and its equipment train. Since no standard directional receiver equipment is available for this use with the T-49, this transmitter is of limited value.

## (2) 400-Megacycle FM Transmitter (T-69)

The T-49 transmitter was abandoned in favor of the T-69 400-mc system as soon as ground receiving equipment for the latter was available. By using the directional receiving set SCR-658 with the T-69 transmitter, the problem of direction-finding and positioning was attacked. A second advantage enjoyed by this system is the improved range attainable.

Our experience has been that an SCR-658 set in good condition can receive a signal up to a range of 150 miles, providing that the line-of-sight transmitter is high enough to preclude blocking by intervening terrain. The use of two or more sets to increase the area of a tracking net is discussed under "Radio Direction-Finding" below.

The operating characteristics of the T-69 system and the SCR-658 may be found in these publications: T.B. Sig. 165, T.M. 11-1158A.

Pressure indicators were obtained, as with the T-49, by use of the modified commutator bar switching specially coded resistors into the circuit as the balloon passed from one fixed pressure to another. A few special tests were made of a chronometric system of pressure modulation. For a complete discussion of pressure modulation methods, see Section VI, A.