Tuneup
Calibration tests
34
August 2004
© Tait Electronics Ltd
Calibration tests
Each calibration test includes step-by-step instructions on how to carry out
the test. Once an instruction has been carried out, select the Next> button.
Forms in which a number of steps must be repeated have an additional
button that loops back to the first instruction that must be repeated.
The calibration test unit's external PTT should be set to Rx for all tests.
Some tests are frequency dependent and so must be carried out across a
range of test frequencies.
Once a test is finished, click on another form or select Edit > Validate Form
to exit the form and save the data, or Edit > Revert Form to exit the form
without saving the data.
AD6521 Volt Ref
The AD6521 CODEC has a single 1.20V bandgap reference for all its
analog-to-digital (ADC) and digital-to-analog (DAC) converters.
AD6521 voltage reference is calibrated using the main power supply voltage.
This is measured at the radio terminals using a multimeter. The result is
entered into the Supply Voltage field, and is used to calculate the AD6521
Voltage Reference Offset.
TCXO/VCO Mod Dev
The TCXO (temperature compensated crystal oscillator) provides the
reference frequency from which all other RF frequencies are derived. The
TCXO requires careful alignment to ensure that the transmitter and receiver
are on frequency.
During this test the modulation deviation is also calibrated.
Receiver
The front end (FE) tuning voltage sets the centre of the bandpass filter in the
receiver section of the radio. The received signal strength indicator (RSSI)
must be calibrated to give an accurate measurement of received signal
strength.
The automatic gain control (AGC) is used to adjust the radio’s gain in
relation to various power levels. The AGC will begin to reduce gain when
the combined signal power of the wanted signal and first adjacent channels
