DANIELS
ELECTRONICS LTD.
TM
3-6
IM10-VR3H040-AB VHF Enhanced Extra Wideband Receiver Instruction Manual
This provides a controlled amount of squelch hysteresis that prevents oscillating action of the
squelch comparator circuitry. The amount of squelch hysteresis is normally factory set for 6 dB
centered about the squelch threshold point. The squelch threshold setting is normally
established as being the point of receiver 12 dB SINAD. The output of U16A is buffered by
comparator U16B before being connected to squelch gate U7. When the output of comparator
U16A to go to the positive rail, the output of comparator U16B also goes to the positive rail
which, baring an active mute line, turns on squelch gate U7. The receiver is now in an active or
unsquelched state. A receiver mute line brought out through main connector pin B28, when
pulled low, acts to permanently squelch the receiver (depending on jumper JU40 and the state of
the receiver squelch override line) by turning transistor Q10 on. Transistor Q10 pulls the
inverting input (pin 6) of U16B to approxi6.5 Vdc which mutes the receiver by causing
the output of U16B to go low, opening squelch gate U7.
Jumper JU40 controls whether the mute line takes precedence over the squelch override line or
vice versa. Jumper JU40 is normally installed giving the squelch override line precedence over
the mute line so if both the mute and squelch override lines are active the receiver will become
unsquelched. To give the mute line precedence, remove jumper JU40.
A receiver squelch override line brought out through main connector pin Z14, when pulled low,
acts to permanently unsquelch the receiver (depending on jumper JU40 and the state of the
receiver mute line) by turning transistors Q8 and Q11 on. Transistor Q8 pulls the non-inverting
input (pin 3) of U16A to the +9.5 Vdc supply which causes the output of U16A to go to the
positive rail which, baring an active mute line, unsquelches the receiver. Similarly, if jumper
JU40 is installed, transistor Q11 pulls the non-inverting input (pin 5) of U16B to the +9.5 Vdc
supply which causes the output of U16B to go to the positive rail which unsquelches the receiver
regardless of the state of the mute line.
3.1.10
COR Outputs
The IF / Audio Main Board employs four methods of interfacing internal squelch circuitry to
external devices, such as transmitters, site controllers, etc. These four methods of COR (Carrier
Operated Relay) control include; an open collector priority COR signal (Q12), an open drain
power MOSFET (Q5), an optional opto-isolated transistor (U17) and an optionally installed
relay (RLY1).
• The priority COR signal, an open collector output (Q12) capable of sinking up to 50
mA when active, is available at pin Z24 of the main connector. Jumper JU39 allows
for internal pull-up to 6.0 Vdc or +9.5 Vdc. The priority COR signal is
derived from the output of comparator U16A so priority COR will become active
anytime the Receiver receives a signal strong enough to trigger the comparator or the
squelch override line is activated. Priority COR is not affected by the receiver's mute
line.
