User Manual

Technical Description
Version 4 4-4 04/02/04
frequency is set by the manufacturer, and can only be changed by
installing another PROM that has the new data written into it.
The “Program Data” data stream is determined by the formulas shown in
Appendix page A-47, Figure 9. These Formulas determine the Program
Reference Counter and Comparative Frequency Multiplier Values sent to
set the desired frequency.
The attached user data processing should key the transmitter a minimum
of 200 milliseconds prior to the application of modulation to the associated
transmitter inputs.
After sending the transmit frequency and keying the transmitter, the
modulation should be applied. When there is no data to transmit, the user
should unkey the transmitter. There is no restriction on the time interval
between the end of the message and when to unkey the transmitter.
4.3.1.2 Frequency Determining and Stabilization
The Model EWI-FLEX-01-HS uses two Phase Lock Loop Integrated
Circuits MB1504. A block diagram of the application of this IC is shown in
the Appendix page A-46, Figure 8.
The PLL-IC employs a pulse-swallow system, comprised of a Phase
Comparator, Program Counter, Swallow Counter, Prescaler, and
Reference Divider. The parameters of the Phase Lock Loop System are
determined with the formulas shown in Appendix page A-47.
The MATHCAD program in Appendix page A-47 contains an example
calculation to determine the programmable values needed to setup the
two PLLchips. The example calculations are for an output frequency of
156.2 MHz uses a step size of 7500 Hz.
4.3.2 Exciter Board Circuit Description
4.3.2.1 Channel Phase-Locked Loop (PLL)
The main function of the channel PLL is to generate a very stable carrier
frequency. The carrier frequency depends on the selected channel. The
frequency range will be 139.3 to 163.3 MHz with a channel separation of
5, 6.25, or 7.5 KHz. The stabilization is achieved by phase locking to the
extremely stable reference frequency generated by reference PLL. Refer
to Appendix page A-44, Figure 6, Exciter Board Block Diagram.