User's Manual

RVP8 User’s Manual
October 2005
TTY Nonvolatile Setups
3–26
PLL ratio of (1/1) ==> Input reference at 17.9876 MHz
The VCXO phase-locked-loop (PLL) in the RVP8/IFD can work with any input
reference clock whose frequency is a rational multiple (P/Q) of half the desired
sampling frequency, i.e., the center frequency of the VCXO that is entered in the
“mc” command (Section 3.2.1). This question allows this ratio to be established. In
general, the best PLL performance will be attained when the ratio is reduced to
lowest terms, e.g., use a ratio of 6/5 rather than 12/10. For example, assume:
VCXO center frequency f
samp
= 36 MHz
Reference clock frequency f
ref
= 10 MHz
f
ref
+
P
Q
Ą
f
samp
2
ĄĄĄ ;ĄĄĄ
P
Q
+
2Ąf
ref
f
samp
+
2 @ 10ĄMHz
36ĄMHz
+
5
9
In this case enter the numbers “5 9”. The proper input reference frequency (e.g.,
10.0000 MHz) should be displayed after you enter the values. The “v” command can
be used to verify that the PLL is “Okay”.
Limits: 1 to 128 for both numerator and denominator.
VCXO has positive frequency deviation: YES
Most VCXOs have positive frequency deviation, i.e., their output frequency increases
with increasing input control voltage. This question will generally be answered
“yes”, but is included to accommodate the other case as well. The PLL will not lock,
and will be completely unstable, if the wrong choice is made.
Enable AFC and MFC functions: YES
AFC is required in a magnetron system to maintain the fixed intermediate frequency
difference between the transmitter and the STALO. AFC is not required in a klystron
system since the transmitted pulse is inherently at the correct frequency.
The following rather long list of questions will appear only if AFC and MFC
functions have been enabled.
AFC Servo– 0:DC Coupled, 1:Motor/Integrator : 0
The AFC servo loop can be configured to operate with an external Motor/Integrator
frequency controller, rather than the usual direct-coupled FM control. This type of
servo loop is required for tuned magnetron systems in which the tuning actuator is
moved back and forth by a motor, but remains fixed in place when motor drive is
removed. These systems require that the AFC output voltage (motor drive) be zero
when the loop is locked; and that the voltage be proportional to frequency error while
tracking. Please see Section 3.2.6.1 for more details.
Wait time before applying AFC: 10.0 sec
After a magnetron transmitter is first turned on, it may be several seconds or even
minutes until its output frequency becomes stable. It would not make sense for the
AFC loop to be running during this time since there is nothing gained by chasing the
startup transient. This question allows you to set a holdoff delay from the time that
valid burst pulses are detected to the time that the AFC loop actually begins running.
Limits: 0 to 300 seconds.