transistor T-l and rj^ is greater than the value 

 of the voltage applied to the transistor when the 

 base voltage is equal to the peak voltage of the 

 tunnel diode. 



If the shift in frequency due to pressure is 

 caused to follow some predetermined schedule, 

 the transistor T-2 can also serve another pur- 

 pose. By rectifying the output and using the 

 voltage to drive the base of the transistor, T-2, 

 we can also perturb the frequency pressure 

 characteristics as a function of frequency. 



EXPERIMENTAL SETUP AMD INSTRUMENTATION 



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A pressure cell was fabricated as shown in 

 Fig. 5- A commercially available germanium tun- 

 nel diode was obtained and the top of the hat 

 carefully removed . Silicone grease was used to 

 fill the cap and it was the only element of the 

 circuitry exposed to pressure. The hydrostatic 

 pressure was applied using an air operated 

 hydraulic pump that permitted setting the air 

 pressure to hold a given hydrostatic pressure 

 during readings. A pressure gage was carefully 

 calibrated and was used to indicate the pressure 

 in the cell. The voltages applied to the cir- 

 cuit were well regulated and instrumented. A 

 Hewlett Packard (Model 52^c-10) counter was used 



Fig. 5- Pressure cell and electronic elements. 



to measure the output frequency. Fig. 6 is a 

 photograph of the test setup. 



EXPERIMENTAL RESULTS 



Using the series amplifier configuration pre- 

 viously described the plot of the frequency vs. 

 pressure shown in Fig. 7 wa - s obtained. Two sets 

 of data are plotted on this curve for comparison. 

 Many additional sets of data were also taken and 

 the results were uniformly the same. A 500 cps 



Fig. 6. Test setup. 



192 



