User's Manual

ALIGNMENT PROCEDURE SST-442
23
RECEIVER NOISE SQUELCH
The noise squelch sensitivity is set at the factory for a
12dB SINAD signal. Using the PC Programmer,
squelch sensitivity can be adjusted on a per channel
basis by adjusting the “Squelch Tightener” number to
between 0-7. The higher number will require a
stronger received signal to open squelch.
1) Select “Channel” from the PC Programmer “Edit”
menu on the main screen.
2) Select the channel to be set and press “Edit”
button.
3) Set the RF communications test set to the
transmit frequency on the screen.
4) Enter a Squelch Tightener number between 0-7.
5) Press the “OK” button on the Channel Edit
screen to return to the Channel List screen.
6) Select any other channels to be set.
7) Press the “OK” button on the Channel List screen
to return to the Main screen.
8) Select “Program Radio” from the PC
Programmer “Radio” menu to save all setting
changes.
SYNTHESIZER
The synthesizer is preset at the factory for operation
between 460 and 470 MHz. There is no manual
adjustment to center the control voltage, with all
adjustment performed by the factory selection of fixed
capacitor C413. Do not attempt to adjust the
synthesizer control unless a key component in the
synthesizer has been replaced. Key components do
not include the Y302 reference frequency TCVCXO or
IC401 synthesizer IC. Synthesizer alignment errors
cause poor operation at temperature extremes.
Should adjustment of the VCO control voltage be
necessary, the radio must first be disassembled and
powered up at 7.5 VDC. The following procedure
defines testing of the VCO control voltage:
1) Select the channel that has the lowest receive
frequency.
2) Connect a VTVM, DVM or oscilloscope to Test
Point 1 and measure the VCO control voltage.
This voltage should be no less than 1.5 VDC.
3) Select the channel that has the highest receive
frequency and measure Test Point 1. The
control voltage should be no higher than 4.5
VDC.
4) a) If adjustment of the VCO control voltage is
required, remove the synthesizer shield top.
b) Replace C413 with a capacitor value that
allows VCO control voltages between 1.5
and 4.5 VDC for the operating frequencies
desired. Decreasing the value of C413 will
raise the operating frequency of the VCO
while increasing the value will lower the VCO
frequency.
c) Replace the top of the synthesizer shield.