Introduction - ozQRP DDS VFO Construction Manual

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NTRODUCTION
The DDS VFO is designed as a companion for the MST transceiver board although it could be
used with most other Superhet or Direct Conversion radios. It is simple to use having only one
control yet offers many advanced features. A short form kit is available containing a PCB with
the DDS chip already loaded as well as the hard to get parts. You only need to add a few
inexpensive components and an hour or so of time and your new DDS VFO is ready to go.
DDS VFO Features:
1. Stable frequency – no more drift!
2. Simple to operate using a single rotary encoder control with press button switch.
3. Bright 16 character by 2 line LCD display. Can also be used with a non-backlight display
to reduce current consumption if needed.
4. Output frequency range of 1MHz to 10MHz.
5. Selectable 1KHz, 100Hz or 10Hz frequency steps.
6. Tuning lock control.
7. Displays power supply voltage.
8. Programmable IF frequency. Ensures the displayed frequency is the same as the
transmitted frequency.
9. Programmable IF offsets:
o Minus – DDS output frequency is the IF frequency minus the displayed
frequency.
o Plus - DDS output frequency is the IF frequency plus the displayed frequency.
o Rev - DDS output frequency is the displayed frequency minus the IF frequency.
o None – DDS output frequency is the same as the displayed frequency. Used for
frequency generator applications or with Direct Conversion receivers.
10. Draws only around 80mA at 13.8V DC (with LCD backlight).
11. Spurious outputs at least -45dB.
12. Typically 300mV pk-pk sine wave output (200 ohms).
13. High quality double sided PCB with ground plane, plated through holes, solder mask and
silk screen.
14. Simple and easy to build using through hole components apart from one SMD chip. To
assist constructors the PCB comes shipped with the SMD chip already installed.
PCBs and a range of kits containing hard to get parts for the DDS VFO and the MST SSB
transceiver are available from www.ozQRP.com.
DDS VFO Construction Manual – Issue 1 Page 4