FM Modulation
OVERMOD Message (Maximum Deviation)
The maximum FM deviation is limited by the following two
conditions:
l Maximum FM deviation must be less than 8 MHz and
l Maximum FM deviation must be less than n x 5 x FM rate
(refer to the “Frequency Bands” specification for the value of n).
The following chart shows the limits of each band given these two
conditions.
For example, in band 1 at a 1 MHz FM rate, the FM deviation must
be less than 5 MHz.
n (1) x 5 x FM Rate (1 MHz) = 5 MHz.
The FM rate can be decreased as long as the FM deviation remains
less than n x 5 x FM rate
and less than 8 MHz.
10
9
xi-
s
8
-7
s
.-
5
6
b
0
5
E
4
E
z
3
',
z
2
1
N
N
N
N
N
6
z
z
5
2
;
2
g&
N
N
3
z
:
88-
z
I
hl
x
aor
G
FM Rate
Figure M-3. FM Deviation and Rate Limits
If the FM deviation is set greater than the 8 MHz limit, it must
be decreased for specified performance. An
O?ERtKiD
message is
displayed on the message line if the FM deviation exceeds
n x 5 x FM rate. Then, either decrease the FM deviation or increase
the FM rate until both conditions for FM deviation are met.
At FM rate levels greater than those shown for each band
corresponding to the 8 MHz FM deviation level, the n x 5 x FM
rate value will always be greater than 8 MHz so the maximum FM
M-18 Operating and Programming Reference
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