DDS VFO Construction Manual – Issue 1
Page 12
TX frequency
The TX (Transmit) frequency is the initial frequency displayed on the LCD at power up. The VFO
DDS firmware uses this value and the IF carrier frequency as well as the IF offset to compute the
actual DDS output frequency.
IF frequency
To generate an accurate output frequency using the equations above, the IF carrier frequency
must be measured and the value entered at configuration. If not the displayed frequency may
not match the transmit frequency.
6.2
P
ROCEDURE
To program the IF frequency, the Transmit frequency and the IF offset type use the following
procedure:
1.
Hold down the encoder button and apply power to the DDS VFO.
2.
Wait until the LCD displays Configuration (about 3 seconds) and then release the
button.
3.
The IF offset screen will be displayed. Pressing the encoder button for less than 1
second will toggle through the options. Once completed press the encoder button for
longer than 1 second and release.
4.
The IF frequency screen will be displayed and the cursor will be positioned on the
10MHz digit. Rotating the encoder clockwise increments the digit while rotating the
encoder anti-clockwise decrements the digit. Pressing the encoder button for less than 1
second will step the cursor onto the next digit. Once completed press the encoder
button for longer than 1 second and release.
Note that if the IF offset has been
disabled this screen will be bypassed as it becomes irrelevant.
5.
The Transmit frequency screen will be displayed and the cursor will be positioned on
the 10MHz digit. Rotating the encoder clockwise increments the digit while rotating the
encoder anti-clockwise decrements the digit. Pressing the encoder button for less than 1
second will step the cursor onto the next digit. Once completed press the encoder
button for longer than 1 second and release.
6.
The DDS VFO will then store the values in non-volatile memory and return to normal
operation.
