The lock-on circuit, consisting of oscillator (¥V-17), amplifier (v-16), the push button switch (S- ), and relay (K-) is used only with the telephone telemetering system. When 4 remote ground . monitoring station is called, a timer holds the line for two minutes. If telemetering for a longer period is required, the lock-on button is pushed which places the 2,00 cps tone generated by the oscillator (V-17) on the telephone line. This line actuates a latching relay at the monitoring station which will hold the line until the Receiving Station release switch is pressed. The 2400 cps tone, its third harmonic (7200 cps) and 60 cps which is often picked up on telephone lines are attenuated by filters F-1,2 and 3 respeotively. The filters prevent these signals from affecting the Receiving Station circuits. The filter circuits remain in the circuit for all types of operation although they are only necessary when using telephone lines and lock-on system. The circuit from this point on, is common to both aerial and ground telemetering. Pulses from the radio receiver are amplified and shaped by V-l, V=2 and their associated circuitry, actuating Sohmitt Trigger, V=3. For each input pulse (Fig. 19a) this stage delivers a uniform sized positive pulse, (Fig. 19b). This is fed through a cathode follower V-LB into a diode coupled (V-5B) step-charger, consisting of capacitors C=-51 and C-52. While one of these capacitors is being charged by the pulses from the Schmitt trigger, the voltage of the other, developed by the previous pulse train, is read by a VIVM bridge (V-11 and V-12) whose output drives the strip chart recorder. Either three decade recorder chart paper san be used to read the intensity -i -