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.

VFO /variable frequency oscillator/ by

2 thoughts on “VFO /variable frequency oscillator/ by

  • November 14, 2016 at 12:16 pm


    I’m attempting to use the alternate optical encoder, EM14A0D-C24-L032S, available for the PA0KLT VFO kit. Is it wired to 20 pin connector on the Si570 board the same as the stock encoder while connecting a 5V supply? My first attempt is not working, something in the connection to the optical encoder pulling down the +5V provided by the Si570 board. Am I wiring it as you’d expect?

    Thank you,

    Ed W2GHD

    • November 14, 2016 at 1:54 pm

      Hello Ed,
      thanks for your post. Unfortunately I abandoned this project and focused entirely on my new project – HF home made transceiver. About the problem with the encoder you can address this issue directly to PA0KLT or SDR-KITS – Jan Verduyn.

Comments are closed.

highslide for wordpress