2.1.2
Radio Telemetry Instrumentation
Each parachute-borne canister containsd an altimeter pressure transducer, two differential pressure transducers (one having a scaie ratio of approximately 3 with respect to the
other), a thermocouple transducer, and a radio telemetry transmitter. Pressure and thermal
stimuli caused each transducer in the canister to frequency-modulate a subcarrier frequency;
the three subcarrier frequencies wore mixed, and subsequently they {frequency -moduiated the
radio-frequency (RF} carrier which was the multiplexing link between the canister and the recording ground station. The ground station contained a separate receiving and recording
system for each parachute-borne canister RF carrier frequeacy. The output of each receiver,
which was a mixture of the three frequency-moduilated subcarriers, was separated by filter
networks. Each frequency was channeled to a discriminator which produced an electrical current proportional to the original stimulus. These currents actuated galvanometers in the recording oscillograph.
The radio telemetry system, measuring equipment, and parachute-borne canisters were
developed and fabricated by the Pacific Division Laboratories, Bendix Aviation Corp., Burbank,
Calif., under Contract AF 19(122)-459. Incorporated in the telemetry ground stations were the
important factors of high mobility in rough terrain, self-sufficient field operation, and accu: acy
of calibration under difficult fleld conditions.
2.1.3
Aircraft Instrumentation
The air-borne APQ-13 radar system was used to position the two B-29 aircraft, both in
reference to time and course position. Various islands in the Eniwetok Atoll were excelient
target points for the radar system. Twelve parachute-borne canisters, six from each P-29
aircraft, were deployed in both Mike and King shots.
The aircraft bomb bays were wired to furnish aircraft electrical power to each canister.
This power was used to preheat the canisters internally during high-altitude operation prior to
canister deployment. The technique of preheating the canisters was necessary to increase
battery efficiency and to stabilize the operation of the electronic equipment. The temperature
inside the canisters was controlled within the range of 70 to 80°F by the use of thermostats and
electric heating stripa instalied in each subsect'ca of the canister. Heat losses were minimized
by lining the inner frame of the canister with a i-in. layer of insulating material.
2.1.4 Canister Instrumentation
The telemetry instrumentation in the canister {s described in Sec. 2.1.2 a8 part of the
radio telemetry system. Two canister parachute systems were designed. The first system, a
dual-parachute assembly, consisted of a 6-{t {ist ribbon parachute and a 28-ft-square sem{ribbon parachuie, The latter parachute was designed for the project at Wright Air Development Center for the specific purpose of minimizing parachute oscillation during canister
descent in order to hold the transmitting antenna as nearly vertical as possible and thus minimize oscillations in the RF signal strength. Immediately afier canister deployment from the
aircraft, the 6-1: :lbbon parachute was released bythe static line attached to the aircraft. The
time of canister descent on the 6-ft ribbon parachute was determined by the canister array
position and ballistic data. An internal timer, set for a predetermined time after canister
13
RESTRICTED DATAa SECURITY INFORMATION
a eid
eter. The hot junctions were variously coated to give a range of sensitivities; thus there were
three types: aluminized (A), natural or uncoated (©), and blackened (DB). The range in sensitivity was less than expected, as explained in slightly more detail in Sec. 2.2.1. To obtain an
output of 1 mv, the irradiation intensities were, respectively, in gram calories per square
centimeter per second, A, 1.49; ©, 1.43; and B, 0.69. The cold junction was shielded ina
cavity mostly enclosed by the lava through which the wires passed; the whole was surrounded
by a massive brass cylinder.
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