Adcon A440, Technical Reference Manual

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36
The A431 Radio Module
If the adjustments do not achieve the appropriate curve, check the power supply,
the cable connections to/from the test equipment, etc. Verify also that all the pins of
the FL1 and FL2 filters are properly soldered.
Figure 18.
Helical LNA’s selectivity diagram.
3.3.9. Adjusting the VCOs
1. Verify that the DUT is in receive mode (enter the RX command at the terminal
program).
2. Adjust the coil L15 (see Figure 17) until the voltage shown on the digital
voltmeter is 1400 mV, ±50 mV (see also the note below).
3. Switch the unit to transmit mode by entering TX at the terminal.
4. Adjust the coil L7 (see Figure 17) until the voltage shown on the voltmeter is
again 1400 mV, ±50 mV.
5. Press the enter key at the terminal to switch the unit off.
Note: A one-time calibration of the Testing Fixture may be needed due to the in-
ternal resistance of the voltmeter and the serial resistor mounted on the Test-
ing Fixture. The calibration is performed by measuring the VCO voltage
directly on the TP2 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 obtained, or the readout is unstable, verify the follow-
ing:
• The programmed operating frequencies are indeed 435 (Band 1), 445
(Band 2), 455 (Band 3) and 465 MHz (Band 4). To check this, type the com-
mand
FREQ at the terminal prompt; the device will answer by returning the
current frequency.
• The respective commands ( RX and TX ) were issued.