Specifications

SMARTUNER MANUAL 45
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so, the frequency is measured and the tuning elements used are saved in memory
coupled with a verification code.
Once saved, a test is made on JP1 to check if the duplex mode has been selected. If so,
the transmit tuning elements remain in circuit until the receive mode is verified. At this
time, all tuning elements are removed.
The frequency is then saved for future comparison and the CPU reverts back to the
STOP mode.
8.2 Tuning Paths
As mentioned previously, various tests are executed to determine the most logical
tuning sequence to be performed. Dependent on the test results, additional tests and
appropriate sub-routines are executed throughout the tuning process. Following are
examples of the activity that occurs when the coupler must be matched to a frequency
that requires a slightly longer or shorter antenna:
8.2.1 Antenna Too Short
C in
L1
50 ohms
Antenna
Once the coupler has verified RF power, the tuning sequence proceeds as follows:
1. Series inductance is added until the phase is deemed as being inductive. At this
point it is normal for the input impedance to be low.
2. Input capacitance is added until the antenna is no longer inductive.
3. The program will continue to increment the series inductance in .25 µH steps—
each time normalizing the input impedance with input capacitance—until a
low VSWR is measured of less than 2:1. This process will continue until the
VSWR has climbed back to higher than 2:1 or the impedance has become high.
4. The settings that gave the lowest VSWR have been kept in memory and are
now recalled to verify it is a low VSWR