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www.sgcworld.com • Email: sgc@sgcworld.com
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the program waits for forward power to cease (if it has not ceased al-
ready) and returns to stop mode. At this point the user should try sev-
eral other frequencies. If the “no-tune” condition persists, check the
installation of the antenna, coupler, radio, and ground system for pos-
sible problems.
Signaling “OK tune.” If the coupler achieves a good VSWR during
the tuning sequence, the program branches to the “OK Tune” section
of the code. Here, the tune indicators are engaged. A test is then made
to check if JP3 is set to tune from memory. If 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.
4.1.2 Manual Mode
Manual Mode allows user to adjust and save settings with or without
RF power applied. See section 6 for details on use in manual mode.
4.2 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 re-
quires a slightly longer or shorter antenna:
4.2.1 Antenna Too Short
Once coupler has verified RF power, tuning sequence proceeds as fol-
lows:
1. Series inductance is added until the phase is deemed as being in-
ductive. 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 .125 µH steps—each time normalizing the input impedance with
SG-239 Manual
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