APEX
™
Exciter Incorporating FLO
™
Technology
Maintenance and Troubleshooting
Exciter Maintenance
Page: 5-8
888-2604-001
03/08/07
WARNING: Disconnect primary power prior to servicing.
5.1.2.2
PLL Board 10 MHz Reference Oscillator Frequency
The PLL board internal 10 MHz reference oscillator frequency is automatically set by
comparing it with the external 1PPS (pulse per second) GPS reference signal in the FPGA
modulator board. The external 1PPS signal is entered at J19 on the rear panel of the exciter.
This oscillator frequency is not adjustable. Any frequency error will be cause by a faulty
PLL board, FPGA modulator board, controller board, or an error in the external 1PPS
reference signal.
The most convenient way to measure the 10 MHz oscillator frequency is by using the
output of W30, which connects to J15 on the FPGA modulator board.
5.1.2.3
Measuring the 1st Local Oscillator Frequency
If it becomes necessary to measure the 1st LO frequency, follow the procedure below.
If this exciter must remain on the air during this test, put the main screen RTAC inputs on
Hold before performing this measurement. Removing the cable from J10 of the PLL board
will interfere with normal RTAC operation.
1
Connect output of 1st local oscillator to a frequency counter. This signal can be ob-
tained from J10 on the PLL board. It should be 128.9 MHz. It is also available at J9,
but disconnecting the cable from it will take the exciter off the air.
A
The output level should be +10 dBm.
2
The 1st local oscillator frequency is affected by the 10 MHz reference oscillator.
A
If the reference oscillator is off frequency, the 1st LO frequency will change
by an amount equal to 12.89 times the frequency error of the reference oscil-
lator.
3
When measurement is finished, normalize exciter connections and screen settings.
5.1.2.4
Measuring the 2nd Local Oscillator Frequency
If it becomes necessary to measure the 2nd LO frequency, follow the procedure below.
If this exciter must remain on the air during this test, put the main screen RTAC inputs on
Hold before performing this measurement. Removing the cable from J5 of the PLL board
will interfere with normal RTAC operation.
1
Connect output of 2nd local oscillator to frequency counter. This signal can be ob-
tained from J5 on the PLL board. It is also available at J6, but disconnecting the cable
from it will take the exciter off the air.
A
The output level should be +10 dBm.
2
The 2nd local oscillator frequency can be found in Table 4-2, 2nd LO Output Frequen-
cies, on page 4-12.
A
If the 10 MHz reference oscillator is off frequency, the 2nd LO frequency
will change by an amount equal to the 10 MHz reference frequency error
times the expected 2nd LO frequency divided by 10.
For example, the 2nd LO frequency should be 549 MHz for channel 50. If the
10 MHz reference frequency measured 10.000020 Mhz, the 2nd LO frequen-
cy would be 20 x 54.9 or 1098 Hz high, for a frequency of 549.001098 MHz.
3
When measurement is finished, normalize exciter connections and screen settings.
