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

decreasing the coefficient of coupling between the primary and secondary of the IF transformers. By this reduction of bandwidth to 3kc a 3 microvolt signal produced a 15.5 DB signal to noise ratio, where at 16 kc bandwidth only 7 DB was obtained.

In order to obtain accurate reproduction of the amplitude of the audio frequency the AVC circuit was modified by adding a fixed bias to the AVC diode of the receiver. This flattened the characteristic of the AVC circuit and no change in amplitude of recorded audio signal was detected over a six hour flight using a constant amplitude audio signal from the transmitter. The signal was tapped off at the output of the second detector of the receiver and fed to a Brush BL 905 AC amplifier for recording. The recorder used was a Brush BL-202 double channel oscillograph. A quarter wave vertical receiving antennae was employed with a counter poise ground. The transmitting antennae was a vertical half wave dipole.

In order to use the AM-1 for transmission of information from pressure and temperature sensors a relaxation oscillator circuit was incorporated in the system. (dotted section - Fig. 6). This oscillator used one half of one of the 3A5 modulator tubes and produced a blocking rate approximately proportional to resistance of the sensor instruments. This information could be superimposed on the regular modulated signal and two types of information could be transmitted simultaneously; one as amplitude and frequency change of the basic signal, the other as a frequency of pulses superimposed on the basic signal.

The AM-1 has been used in balloon control research to transmit information on pressure, temperature and ballast requirements. It was also employed to give information on Neutron intensities in another Air Force project(5). In order to obtain information on balloon position on a wind study project the AM-1 was used as a beacon to be "homed in" on by the radio compass of aircraft(6).

A system of diversity reception was considered for use with a dual channel AM-1 transmitter in order to increase reliability despite atmospheric noise. In the dual channel unit a common modulator was connected to two separate crystal oscillators and RF amplifiers. In preliminary tests two receiver and recording units were used.

For short range balloon flights the AM-1 was modified for use with subminiature and acorn type tubes. In this, the AM-2, two 2E27 tubes in parallel provide excitation for the type 958A RF amplifier. A circuit diagram of this unit is shown as Fig. 7.