specifically cut to operate on the frequency of the transmitter (138 

 megacycles, in this case). 



RECEIVER 



The receiver is tunable from 55 to 260 megacycles and was chosen for 

 its excellent sensitivity, stability, and low noise figure which permits 

 the system to receive signals from the buoy over the greatest possible 

 range. The receiver also has a type of discriminator which produces a d-c 

 output voltage that is quite linear for input frequency change. It has 

 been modified to bring the output of the discriminator out to the back 

 panel. 



LOW- PASS FILTER 



The output from the wave-height buoy contains acceleration informa- 

 tion caused by the high-frequency short waves which contribute little energy 

 to the wave spectrum in the frequency range of interest. This information 

 will, in fact, mask the desired lower frequency accelerations of the impor- 

 tant gravity wave range. To eliminate the undesired information, an 

 electronic low- pass filter is used. The output of the receiver is fed 

 into the low-pass filter which has adjustable cutoffs at a number of 

 frequencies (Figure 5) . This filter eliminates the higher frequency 

 signals while passing the desired signals. The filter was specifically 

 designed to drive the record amplifiers of an FM tape recorder. However, 

 it may be used with direct writing recorders as well. The filter system 

 was developed at the David Taylor Model Basin. ^'"^ 



RECORDING 



The data received from the wave-height buoy system can be recorded 

 on any one of several types of recorder. It is usually recorded on a 

 magnetic tape using FM electronics because this permits the information 

 to be played directly into the Taylor Model Basin spectrum analyzer. The 

 data could also be recorded on a strip chart recorder using the proper 

 driving amplifiers. This would allow immediate access to the raw data. 



