Receiver Front-End Tuning
Note: Connect the MON input (modular jack pin 4) to ground (modular jack pin 1). This will keep the Squelch function
from muting the receiver.
1. Connect a SINAD meter to the AUDIO OUT output (pin 5) to Ground (pin 1). Set R330 (SPEAKER AUDIO LEVEL) to
mid rotation.
2. Set the generated output of the Service Monitor to the desired receive frequency modulated with a 1 kHz tone at 1.5
kHz deviation. The RF level should be set to 7uV (
–90dBm).
3. If the SINAD meter reads greater than 12 dB, reduce the RF signal generator output level until 12 dB SINAD is
reached. Adjust L101 through L104 for best SINAD while reducing the RF signal generator output level to keep the
SINAD near 12dB. The RF output level for 12 dB SINAD should be 0.25uV (-119dBm) or less. Note that all of the
inductors have a very broad tuning characteristic, except L103. Adjust the inductors in the middle of this broad range.
Squelch
1. Set the RF signal generator output level to produce a SINAD reading where the squelch is desired to unmute, typically
12-14dB. Remove the wire jumper from the Monitor Input (pin 4) of the RJ11 connector.
2. Rotate R312 (SQUELCH) to the maximum counterclockwise point. Connect an oscilloscope probe to TP104. The
voltage at TP104 should be 5 VDC. Adjust R312 clockwise until the TP104 voltage drops to zero. Then, slowly adjust
R312 counterclockwise to the point where the TP104 voltage again goes to 5 volts. Conversely, if ‘override tone’ is
set for squelch mode in the programmer menu, one can listen for the presence or absence of audio at the audio
output to determine the squelch point.
Содержание Liberty RLR-460
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