Comtech EF Data SFC4200 - Manual (Page 43)

SFC4200/SFC1275G Synthesized Frequency Downconverter User Interfaces
TM054 - Rev. 4.0 4-19
DAC Value: Place the cursor in the DAC Value Field and use the (
↑↑
)
and (
↓↓
) Keys to increment or decrement the DAC Value.
Simultaneously, the display will indicate the DAC
Voltage. In a normal calibration arrangement, the
operator will be monitoring the power output of the
converter with a Spectrum Analyzer. When the desired
value of calibration is reached, the operator will depress
<ENTER> which stores the value and increments the
Atten Level to the next number. The DAC value will
revert to the stored value for that location. This keypad
arrangement is designed to allow for manual calibration
with limited wear-and-tear on the operator who may be
attempting manual calibration of the attenuator in the
field.
To perform the calibration, the technician needs to apply
an RF signal to the Downconverter at the frequency
indicated in the Freq. Field. A spectrum analyzer or
power meter is connected to the output and the DAC
Value is incremented up or down until the required gain
is indicated by the spectrum analyzer. Finally, the
correct DAC is stored by depressing <ENTER>. The
attenuator setting is incremented to the next location, or
in this case, 01 dB. The process is repeated until 20 dB
is reached and then the next frequency is selected. The
frequency of the signal generator must be changed and
the process repeated. This menu is not displayed when
the converter is online.
4.3 Serial Protocol
The SFC Downconverter Serial Protocol allows a remote operator to gain control the converter.
Through the serial protocol described, the remote operator can control gain, frequency,
calibration, status and fault isolation. The Serial Port is factory-set to communicate as the DCE
at 9600 baud with 8 data bits, 1 start bit, 1 stop bit and no parity bits.
4.4 Command Structure
The serial command structure uses an ASCII character string format that enables serial control
through the use of a ‘dumb terminal.’ To differentiate a proper command string from noise, all
serial commands have a header followed by the specific command characters, followed by
numeric values where required, and are terminated by a character return <cr>. The basic
command structure is as follows:
@{Unit Address/}{command}{numerical value(s)}<cr>
For the following examples, a unit address of 01 is assumed.