Digital VFO
80m/160m Digital VFO
VFO front panel controls include coarse and fine frequency adjustment as well as switches for ‘spotting’ and 80m/160m bandswitching. There are also back-panel outputs provided to activate 80m/160m bandswitching circuits and provide VFO Activated signals for transmitter interlock circuits.
80m/160m Digital VFO
The VFO uses a hartley oscillator operating at 40 meters. The 40 meter signal is divided either once (80m output) or twice (160m output) by a flip flop IC, providing TTL signals to IXDD414 driver ICs. The VFO IXDD414 outputs are 12V square waves, Phase 1 and Phase 2.
The VFO has its own power supply, and a sturdy internal .125” aluminum enclosure for the oscillator.
VFO Back
VFO outputs include a low level frequency counter output, two outputs (Phase 1 and Phase 2) for the RF amplifier modules, PTT input to activate the VFO, VFO On dry contact output for transmitter interlocks, and 160m Select output dry contact for external bandswitching circuits. A heat sink is used to prevent internal heating by power supply regulators, rectifiers and IXDD414 drivers.
VFO Outputs, 80 meter at 12V pk-pk
After initial construction was complete this VFO was modified to include the latest WA1QIX circuit revision. This modification installed IXDD414 drivers on the PHASE 1 and PHASE 2 VFO outputs. This change boosted the output from TTL to 12V.
Additional changes to the original design were added by me. These included changes to the oscillator resonant circuit to fit the enclosure. A third variable capacitor was also added to the oscillator so that the front panel ‘coarse’ frequency adjustment would span the desired 160m and 80m frequency ranges. The ‘fine’ frequency adjustment spans 22khz on the 80m band, and 11khz on the 160m band. A 160m Selected output was added, and VFO Active indicator LED was added to the front panel.
Digital VFO Construction/Testing
Divider Circuit
Oscillator In Enclosure, With Divider Circuit
VFO Covers Removed
Oscillator Circuit
80m Testing
Oscillator and Divider Circuit Outputs
160m Testing
Oscillator and Divider Circuit Outputs
The VFO was designed by Steve Cloutier WA1QIX. The design revision used to build this VFO is detailed in this schematic. The current revision of this schematic may be found at www.classeradio.com