Received signal voltages at the preamplifier impub measured about 100 

 and 500 microvolts (u.v.) at 1 mile. These levels were at least 20 

 decibels (db) above the ambient noise levels at the receiver output. 

 A measurement of receiver-system noise showed that the self- noise of 

 the receiver- pre amplifier combination is 6 db below 0.09 >i.v. at 21 kc, 

 which shows a tremendous margin of sensitivity for use in quiet waters. 

 Of course, use in oceanic water will afford much better ambient noise 

 conditions than Biscayne Bay, which was full of motor vessels and bio- 

 logical noisemakers. 



As expected, multiple-path transmission caused extreme variation 

 in signal strengths during this test, and it was difficult to establish 

 exact figures for directivity. The fading was strikingly similar in 

 amplitude and period to that experienced in low- or medium-frequency 

 radio transmissions at or near ground-wave limits. Amplitude excursions 

 of 20 db were noticed under certain conditions. 



At distances of approximately 1 mile, variations in the position 

 of the transmitting transducer within a 40° horizontal angle did not 

 seriously affect the received signal. Transmission, at times, was 

 obtainable with reflected energy from the large stone breakwaters 

 100 feet behind the transmitter. At 1,500-foot range, overload of the 

 receiver was experienced and extremely strong signals were received 

 regardless of the transmitter's direction. Test personnel aboard the 

 motor launch were able to hear the received tone from the receiver 

 loudspeaker on shore, a distance of 2,000 feet. 



The KE-2 hydrophone assembly was suspended by rope from a pole 

 at the seawall at the southeast corner of the Coast Guard base. Move- 

 ment of this unit to determine directivity characteristics indicated, 

 as would be expected, a much broader pattern. The receiving pattern 

 seemed to be about 20° or 30° wider than that of the QBG transducer 

 transmitter. 



The above observations were made at 21 kc. (the surface frequency). 

 Transducer gain will be greater at the higher frequencies, due to the 

 sharper directivity patterns expected, and the figures given here may 

 vary widely. 



Depth 



A trip to sea aboard the K/V GERDA was made for depth tests in 

 order to check pressure housing and seals of the telemeter transmitter. 

 Inasmuch as seas were moderate and there was a wind of about 10 knots, 

 it was impossible to lower the telemeter without a considerable cable 

 angle. This angle increased with depth and made it impose ibis to 

 ascertain the exact depth of the telemeter transmitter. Therefore, 



17 



