calibration adjustments, respectively. G-, (type 1N54-A germanium 

 diode) functions as the a.g.c. rectifier and supplies the control 

 bias for the variable mu amplifier, V-^. Positive feedback is 

 adjustable by means of R~, which, of course, sets the level of 

 oscillation. This is adjusted so as to provide -5 volts, d»c. at 

 point A, as measured with a vacuum-tube voltmeter. This adjustment 

 is made at the lowest operating frequency. 



Vq (1R5) follows V-|_ and V 2 and serves two purposes: it acts as 

 a buffer amplifier between the oscillator and driver, V^, and it is 

 ussd as a modulator that mixes the depth and temperature signals so 

 they may be transmitted together. The plate circuit of V^ contains 

 a single section — constant k, T high-pass filter — which has a low- 

 frequency cutoff of about 10 kc. It prevents the modulating signal 

 (about 200 to 800 c.p.s.) from appearing at the grid of the class-A 

 driver, Vo. The carrier level is adjusted independently of modulation 

 level by R-jr and is set while observing the output waveform at the 

 secondary of T 2 when it is properly loaded. 



Vo (3V4) operates as a class-A amplifier and supplies the energy 

 necessary to properly drive the grid of Vi , the U6GT class-B power 

 amplifier. 



The class-A driver and class-B output transformers, T-, and T 2 , 

 and the filter reactor, L^, were designed and wound at the "Marine 

 Laboratory. The modulating signal is supplied by the temperature 

 oscillator, Vr, a 3V4 blocking oscillator. The temperature- sen sing 

 element is a type 51R2 thermistor made by Victors'- Engineering Co. 

 It is encased in a special oil- filled brass housing, which is screwed 

 into the end cap of the instrument. High -temperature and low-temper- 

 ature limit calibration adjustments are provided by R20 and %2> 

 respectively. The "sawtooth" output from Vc is shaped by an R-6 net- 

 work, described above. In reality, this is not an undesirable effect. 

 Modulation would be increased in colder water., which, in general, 

 would be deepest. A slight saving in battery power may result at 

 shallow depths, where the water is warmest. 



Of course, other information could be impressed on the 

 carrier by means of the moduLator, which, when tested in the labor- 

 atory, was fairly linear. Adjustment of modulation percentage, 

 independently of carrier level, may bo made by R2r. This adjv«3tment 

 should be made at the low-temperature limit, while observing output 

 waveform at the secondary of T 2 in order to avoid overload, which 

 would cause a multiplicity of sidebands and make it difficult to 

 identify the carrier on. the telemeter receiver. 



The transducer is affixed to the telemeter housing with a cLianp 

 that allows positioning at various angles in order to pre-set its 



