Milltronics Level Genie, Instruction Manual

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Q6 and Q7 provide additional amplification. Q7 also
serves as a detector charging C9 with the positive half-
cycles of the received signal.
Q8 is turned on during the blanking period to prevent
C9 from accumulating any charge. Thereby precluding any
receiver output during this time period,
When the voltage on C9 reaches about 1 volt, Q9 turns on
and the voltage at the collector of Q9 falls to zero signifying
reception of an echo.
The network formed by D3, R25, and Cl1 provides a delayed
receiver output which responds only to signals of a half milli-
second duration or longer.
Noise spikes of short duration are
therefore ignored.
3. As a Transmitter
Q2 and Q5 control the change over from receiver to trans-
mitter.
During transmit time, Q2 is turned on dissabling Q3
and Q5 is turned off releasing Q4 to operate in place of Q3.
Q4 and Q6 are in a closed, positive feedback loop which
oscillates at the frequency to which the primary of Tl and C5
are tuned ie.
at the receiver's operating frequency.
Two gates of IC-7 form a monostable multivilrator. During
transmit time, pin 9 of IC-7 is held low allowing the monostable
to product a string of pulses each a little less than a half
cycle of transmit frequency but spaced exactly a half cycle apart.
QlO, Qll, and Q12 amplify these pulses in class C fashion and
apply them to the primary of transformer T2. T2 increases the
signal to about 350V peak-to-peak to drive the transducer.
3-2