Multitone BSR 113, Техническое руководство, Страница: 21 / 63

BSR 113
TM1194A Issue B Page 3 - 7
Table 1: Noise Squelch Signal Levels
LEVEL SIGNAL
5V NOT RECEIVED
0V RECEIVED
Signal Indication and Noise Squelch Defeat
21. When the collector of TR49 goes high TR27 is turned on allowing current to flow
through the LED D11, thus providing a receive signal indication. The collector of
TR49 can also be held permanently high by fitting LK1, providing a noise Squelch
defeat facility.
Signal Detect Reed Relay
22. When a squelch signal of 0V (i.e. signal received by the receiver) is placed on the
base of TR11 it is switched off. This in turn 5V on the base of TR12
which switches on, allowing current to flow through the relay coil of RL1. When
current flows the relay contacts close. The contacts are connected to auxiliary
socket SK1 (pins 3 and 5).
Signal Strength Tone Circuitry
23. The rectified output from the collector of TR28 is known as DC SQ and is fed to
a DC buffer (IC6). The resulting DC level is passed to IC2 (pin 5) which acts as
a Voltage Controlled Oscillator (VCO) running at approximately 12kHz. The
frequency of the output (pin 3) is dependent on the DC level of the input (pin 5).
A higher level of incoming DC squelch signal produces a lower frequency oscillator
output, and vice-versa.
24. IC3 is a quad D-type flip-flop which divides the VCO output by four to obtain
approximately 3kHz and provides a square wave output. The signal then passes
through two stages of band-pass filtering provided by IC6.
25. The frequency of the signal strength tone output varies from about 2.7kHz for a
receiver RF input level of approximately -100dBm (and above) to approximately
3.2kHz for an input level of approximately -120dBm (and below). Fine adjustment
of the signal strength tone frequency is provided by RV1.
Tone Out Driver
26. The output from the Signal Strength Tone circuitry is fed, via audio gate TR30, to
the Tone Out driver amplifier IC8 (pin 5). In normal operation link LK14 is fitted
and the Tone Out signal is gated by the noise Squelch via gate TR18 or the signal
is continuously running dependent upon the application. For full voting LK14 is out.