64
3314A'1
At this time, there are 2 primary concerns which preclude acquiring phase lock.
.72
B.W.
(OISPLA::O FREQ )
where A
1 if the EXT REF FREQ is
<
2MHz
A
=
5 if the EXT REF FREQ is
2MHZ
MODE
(cant)
Use the VCO input if you have
8
signal that is proportional to the reference fre-
quency. You will probably have to turn auto-acquisition off with FREQ Range Hold
and set the 331 4A's center frequency manually. Any error between the VCO in-
put s
ignal
and the reference frequency must be corrected by the 3314A's PLL and
hence, must be within the loop bandwidth. The 3314A's output frequency can
range
+
10% to -50% without losing lock.
Note that
when
the
3314A's
output frequency deviates
>
10%
from
the
displayed frequency, one of the
LCK lights will flash. This does not necessarily
I
ndicat e an out of lock condition.
2. The reference frequency change must be within the bandwidth of the 3314A
's
phase locked loop.
The 3314A's phase
-lock
capability can
be
greatly extended if you pre
-tune
its
oscillator frequency using the VCO or FM modulation capabilities.
1
.
The 331 4A's output frequency is limited to
+
10% and -50% of the displayed
value.
Note that the 331 4A will not update its frequency d
isplay
unless the loop goes
out of lock (the Fin
N light flashes) and Frequency Range Hold is OFF.
The approximate bandwidth of the phase locked loop can be determined using this
formula:
