Technical Manual

17
Tuning
3.3.4. Adjusting the VCOs
• Flip the switch on the Testing Fixture to the
Power/Sens.
position;
• Be sure that the DUT is in receive mode (enter the
RX
command at the terminal
program);
• Adjust the coil L10 until the voltage shown on the digital voltmeter is 700 mV,
±50 mV (see also the note below);
• Switch the unit in transmit mode, by entering
XMIT
at the terminal;
• Adjust now the coil L6 until the voltage shown on the voltmeter is again
700 mV, ±50 mV;
• Press the enter key at the terminal to switch the unit off.
Note: If using the Testing Fixture, a calibration may be needed, due to internal resistance of the
Voltmeter and the serial resistor mounted on the Testing Fixture. The calibration is performed
by measuring the VCO voltage directly on the TP1 and by comparing the value with that
measured through the Testing Fixture. The values given above are the real ones, measured di-
rectly.
If the above limits cannot be attained, or the readout is very unstable, check the fol-
lowing:
• If the programmed operating frequency is 432 (Low Band) and 450 MHz
(High band) respectively. To check this, type at the terminal prompt the com-
mand
FREQ
, the device will answer returning this parameter;
• If the respective commands (
RX
and
XMIT
) were issued;
• If some parts are not missing, have the incorrect value, or badly soldered
(check the parts around Q2 and Q6).
3.3.5. Checking the Receiver Parameters
• Check that the switch on the Testing Fixture is flipped to the
Power/Sens.
po-
sition;
• Switch the DUT to receive mode by typing at the terminal the command
RX
;
• Switch the Service Monitor to RX TEST mode, on the appropriate frequency
(432 MHz for low band and 450 MHz for high band); the level should be 5 µV
(see also “Test Equipment Settings” on page 15);
• The S/N ratio should be at least 10 dB; in addition, if a ‘scope is also connected
a clear 2 kHz sine wave should be visible, with a relatively low amount of
noise superimposed;
• Switch the DUT in pulsed mode (press the enter key);
• After several seconds, you will see the image on the ‘scope pulsing at about
one second intervals;
• Switch the RF generator output off;