of T2 when loaded by 150 ohms. It shows a compression of modulation 

 due to non-linearity in the class-B anplifier, V, , at the 2-watt 

 level. Voltage at this point is about 50 volts peak-to-peak. 



The 21-kc. carrier is shown at the top of figure 4 as it appears 

 at the mixer grid, point B. The voltage at this point is 10 volts 

 peak-to-peak at 21 kc. The slight distortion caused by the a.g.c 

 diode can be seen on positive waveform peaks. The fuzzy waveform 

 peaks are due to coupling of a small amount of modulating voltage 

 through the B+line. Increasing the size of C 2 > and substituting a 

 choke for R,, would eliminate this problem; however, no deleterious 

 effects upon the operation were noted, and the necessary extra space 

 was not available. The depth oscillator showed a very slight tendency 

 to lock to harmonics of the temperature or modulating waveform and 

 when waveform peaks coincided; however, pulling was very slight. 



The modulating waveform shown at the bottom of the second polaroid 

 photograph (fig. 4) was taken at point C, and it measured 3.2 volts 

 peak-to-peak at 520 c.p.s. It is a modified sawtooth, which is altered 

 by the network containing R 2 v -^24* ^2 ( 5 > ^17* ^18' an< ^ ^2* 



Receiver 



The telemetering receiver used in this system is a Navy-model 

 R3A-6, low-frequency, radio receiver type CJT 463OO. It is used in 

 an unaltered condition; however, the system required auxiliary re- 

 ceiving equipmsni. This auxiliary equipment consists of a cathode- 

 follower transducer isolation amplifier and a low-noise, high-gain 

 preamplifier. These units are described below. 



A cathode- follower amplifier, V„ (6AH6), is contained in the 

 receiving transducer housing and is powered through the multi-conducter 

 cable connecting it to the preamplifier at the receiver. Vy is used 

 to isolate the crystal receiving transducer from the low-impedance 

 cable connecting it to the preamplifier, and thus it prevents loading. 

 This tube also provides a low-impe dance source to drive the bandpass 

 filter located in the preamplifier, An electrical schematic drawing 

 of these unit 3 is shovn in figure 5. 



A preamplifier consists of two tube3, Vg and V Q . Vg is a 

 6BK7A, which is used as a high-gain, low-noise, cascade amplifier, 

 and Vo. is a 12AU77j which is used as a triode amplifier and cathode- 

 follcwer output. A bandpass filter is used at the input- of the unit 

 to exclude undesirable electrical voltages outside the frequency range 

 used for telemetry and to prevent cross-modulation and generation of 

 unnecessary interference. The bandpass of this filter is 1.5 to 100 kc, 



8 



