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microcomputer memory and begins the termination of
tuning sequence.
5.4.6
Termination of Tuning Sequence
U8-33 goes high to allow the radio to revert to
the receive mode. The microcomputer memory retains a
list of the circuit elements that were switched in when
the sequence ended. Circuits elements remain selected
until there is a voltage transition at ANT TUNE (VIa),
SWITCHED A + (GRN), or CHANNEL CHANGE
(BLU). Tuner operation following these transitions is
described in the following paragraphs.
5.4.7
Transition At ANT Tune (VIa)
A voltage transition on the ANT TUNE line in-
dicates a change in radio channel from an A channel to
a B channel, or vice versa. The voltage transition is ap-
plied via U5F and U9 to U8-1I. All tuning elements are
switched out and the microcomputer begins initializa-
tion and 4: 1 VSWR detection.
5.4.8
Transition At SWITCHED A + (GRN)
If voltage is removed from the SWITCHED A +
line, the list of selected circuit elements stored in the
microcomputer memory is lost. When power is reap-
plied to the SWITCHED A + line, the microcomputer is
reset and the initialization and 4: 1 VSWR detection pro-
cess begins.
6
5.4.9
Transition At Channel Change
When a channel is changed using the channel"-~
selection knob on the radio, a positive going pulse is ap- .
plied to the CHANNEL CHANGE line (BLU). A low is
applied to U8-34 and U8-39 to inhibit tuning until chan-
nel selection is complete. One-half second after channel
selection is complete, there is a low to high transition at
U8-34 and U8-39 and a high to low transition at U8-28.
The microcomputer then goes through initialization and
4: 1 VSWR detection.
5.4.10' Tune Power Variations
)
'I
j
5.4.10.1 If, during a tuning sequence, the tune power
level falls below 1 watt or rises above 6 watts
for more than two seconds, the tuning sequence is stop-
ped. The tuner reverts to the circuit configuration pre-
viously stored in the microcomputer memory. This con-
figuration:y> used for antenna matching until there is a
channel change and the tune power is between I and
6 watts.
When these two conditions
are met the
microcomputer
goes to initialization and 4:1 VSWR
detection.
5.4.10.2 If tune power falls outside the 1 to 6 watt range
for less than 2 seconds, the microcomputer
resumes the tuning sequencethat was underway prior to
0""""
the level change.
(,.)'
1
.~
;1
..
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