Category Archives: PA0KLT VFO kit Si-570

VFO /variable frequency oscillator/ by

Here I will share my experience with PA0KLT VFO kit.

VFO kit based on Silicon Labs digital synthesizer chip Si-570 arrived too fast from UK with ordinary post service /a week or so/. I purchased new version with implemented additional buttons for RIT and FAST functions .. also with ability to exchange the main mechanical tuning knob with optical encoder. Building the unit is not difficult at all and passed straight forward… even placing Si570 chip is not a pain.


The unit comes to alive from first attempt. I’ve used it for two months now with my multiband BITX – home made transceiver.

I like that it has rock solid frequency stability and accuracy. It has well organized config and memory menu for calibration, writing in memories, assigning IF /intermediate frequency/. Mode selection – CW, USB, LSB and AM. Two VFO’s and memories

What I dislike is:

1. It cannot memorize the last position of the VFO when shutting down… After switching power supply on again it always runs from VFO A?!

2. Band decoding is not correct according the manual. The table in the manual is not correct. Then I decided to contact PA0KLT directly so he did send me correct band decoding tableHere I suggest another table which is more suitable for BITX multiband transceiver.

3. IF shifts for CW/USB/LSB cannot be adjusted separately. For LSB/USB it is assigned to be ±1.5kHz and for CW ±0.75kHz which is not flexible and limits the use of different crystal filters /wide and narrow/ .. also different positions of the carrier crystals. In those cases the frequency shown on LCD would be incorrect!

4. The microcontroller used in the VFO does not support other type encoders with more PPR /more than 25ppr/ … so the tuning speed is way too slow so use of X5 rate or ‘< ‘ ,  ‘>’ buttons are mandatory.

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