User Manual

Technical Description
Version 4 4-2 04/02/04
deviate the NCO to generate the instantaneous signal for the 10.7 MHz I/F. The
maximum deviation is limited to +/- 5 KHz.
In the digital mode the MFSK data will be sent two bits at a time to the Hi Stability
exciter along with data clock, or just one bit of data and clock when in the FSK
mode. After the key line is deactivated, the microprocessor sends the debounced
inactive key line to the RF exciter and sets the RF exciter center frequency to the
default center frequency selection. The Control U PCB presents onboard LEDs
for indication of +5 volt power on, key active, data input, and frequency
programming active.
4.2 CONTROL “A” BOARD
The Control A (Analog) is simply a collection of all of the analog functions
required by the transmitter to accomplish its tasks. The Control A board is
typically the first point in the transmitter that all audio (analog) signals are routed
to. All incoming audio is transformer coupled (600 ohm) on transformer T1. The
full schematic for the Control A board is contained on Page A-21
The signal flow of the Control A board shows the amplification of “incoming”
audio signal. After the audio is received by the input transformer T1 it is gated by
a processor controlled digital switch U2. The control of this switch originates with
the master processor on the Control U board and is passed over to the Control A
board via the backplane. The incoming audio is routed by U2 to an input buffer
amplifier U8A where the level is raised sufficiently to drive the output audio
amplifier (U1B) circuits. Audio from the final audio amplifier (U1B) is switched via
U2 to the exciter. Digital data is routed from the Control U board via the
backplane to the Control A board where it is presented to an amplifier (U1A) for
deviation and offset adjustments. The conditioned data is then sent via U2 to the
exciter. A simplified flow diagram of the audio and data paths through the
Control A board is shown in appendix A-23.
The input audio level into the first audio amplifier is somewhat dependent on its
source and other external factors, but should be about 1 Vptp. All factory
adjustments are referenced to this input level. The audio level at TP5 should be
set for 3 volts Peak to Peak under normal input conditions by adjusting R14.
Adjusting R1 sets the analog deviation while the digital deviation is set by R30. If
an offset adjustment in the DC level of the digital data is required (normally not
required) this is accomplished by R29.