The 18 November deployments 

 from low altitudes while maneuver- 

 ing were only partially successful. 

 A clear signal was initially received 

 from each AXBT, but static noise 

 soon began to interrupt the AXBT 

 signal. This interference eventu- 

 ally caused a premature signal 

 loss. As a result, neither tempera- 

 ture profile could be read after GO- 

 SO m. 



There are four possible causes of 

 the observed signal loss: (1) 

 premature scuttling of the AXBT 

 surface transmitter; (2) high sea 

 state; (3) loss of line-of-sight 

 between the AXBT transmitter and 

 the aircraft receiver; and (4) wire 

 break. Since the aircraft was 

 maneuvering at low altitudes and 

 numerous white caps could be 

 observed on the sea surface, any 

 one of these could have caused 

 the signal loss on 18 November. 

 The second HC-130H test (7 

 January) sought to determine the 

 cause of the premature signal 

 loss. 



Before the actual testing, avionics 

 technicians from Coast Guard Air 

 Station Elizabeth City, North 

 Carolina, conducted bench testing 

 of the VHF receiver and cassette 

 recorder. The results showed that 

 the receiver was sensitive enough 

 to receive the AXBT signal; the 



receiver and the aircraft VHF-FM 

 antenna were compatible; and the 

 receiver's audio output was large 

 enough for the for the audio signal 

 to be recorded on tape. In short, 

 the bench testing on the ground 

 indicated the AXBT receiver and 

 recorder should work on the HC- 

 130. 



On 7 January, four AXBT's were 

 deployed over a three hour period 

 during an operational Coast Guard 

 flight. Ail four deployments were 

 successful. Good signals were 

 received from all four AXBT's. All 

 AXBT's transmitted for a period of 

 time equivalent to a complete 300 

 meter drop. The data from 

 deployment 2 had some interfer- 

 ence towards the end of the drop. 

 Deployments 1 and 2 were both 

 done from 8000 feet, but the 

 aircraft increased speed to 250 

 knots after the AXBT was de- 

 ployed on deployment 2. At this 

 speed, the aircraft was 5 nm 

 farther from the AXBT than at 1 50 

 knots after three minutes. At first, 

 this does not sound like a signifi- 

 cant difference. Relatively speak- 

 ing, however, the aircraft was 40 

 percent farther from the AXBT at 

 250 knots than at 150 knots after 

 three minutes. 



Deployments 3 and 4 occurred 

 over 2 hours after deployments 1 

 and 2. The entire data record 

 from deployments 3 (at 4500 feet) 

 and 4 (at 8000 feet) was noisier 

 than either of the previous deploy- 

 ments from 8000 feet. The 

 increase in noise in the tempera- 

 ture profile from these two deploy- 

 ments might have been caused by 

 increased sea state from a coastal 

 storm which was moving into the 

 drop area. 



HU-25 Testing 



Tests were conducted from the 

 HU-25 on 22 December and 21 

 January 1988. Four AXBT's were 

 deployed on 22 December. Due 

 to a problem with the cassette 

 recorder recording the AXBT data, 

 the data from this test were not 

 recoverable for later playback and 

 analysis. It was later learned that 

 the cassette recorder was tem- 

 perature sensitive. Changes in 

 temperature caused the recorder's 

 tape speed to change. Without a 

 frequency standard introduced at 

 the time of recording, the recorded 

 data were not recoverable. 



92 



