APEX
™
Exciter Incorporating FLO
™
Technology
Theory of Operation
APEX Exciter Analog Assembly Overview
Page: 4-12
888-2604-001
03/08/07
WARNING: Disconnect primary power prior to servicing.
4.4.3.3
Main Phase Lock Loop (Second LO)
Refer to Figure 4-9, Second LO Block Diagram.
The second LO covers 197-663 MHz. It is referenced to the 10 MHz reference oscillator,
which is locked to GPS. It is used to convert the 140 MHz (center channel) second IF to the
desired channel center frequency.
The second local oscillator PLL generates a CW signal which is 140 MHz above the
desired center channel frequency for VHF channels and 140 MHZ below the desired center
channel frequency for UHF channels. Refer to Table 4-2 for a list of frequencies for
channels used within the USA.
A single loop PLL, locked to the 10 MHZ reference oscillator is used to set the 865 MHz
to 1180 MHz VCO to a specific frequency within its frequency range. This chosen
frequency is applied to a divide by N circuit, where N is chosen so that its output, or a
harmonic of its output, falls on the desired second LO frequency. A tunable bandpass filter
is controlled via the micro controller to select the desired frequency and assure that the LO
output is clean.
Figure 4-9 Block Diagram Main Phase Lock Loop (2nd LO)
Table 4-2 2nd LO Output Frequencies
Channel
Frequency Range
2nd LO Frequency
Channel
Frequency Range
2nd LO Frequency
Standard channels for USA
FLO RF channel 1 through 8 for USA
2
54 - 60 MHz
197 MHz
1
698 - 704 MHz
561 MHz
4 MHz gap between channels 4 and 5.
2
704 - 710 MHz
567 MHz
6
82 - 88 MHz
225 MHz
3
710 - 716 MHz
573 MHz
7
174 - 180 MHz
317 MHz
4
716 - 722 MHz
579 MHz
13
210 - 216 MHz
353 MHz
5
722 - 728 MHz
585 MHz
14
470 - 476 MHz
333 MHz
6
728 - 734 MHz
591 MHz
69
800 - 806 MHz
663 MHz
7
734 - 740 MHz
597 MHz
8
740 - 746 MHz
603 MHz
2nd LO Output to Up
Converter, +10 dBm
2nd LO Output to Down
Converter, +10 dBm
10 MHz
Reference
Input
2-Way
Splitter
Low Pass
Filter
U36
865 - 1180
U45, Phase
÷
M
MHz VCO
U47
Tunable
Band Pass
Filters
Locked Loop
÷
N
