A few weeks ago Ton (PA0KLT) asked me to test a new developed VFO by SDR-kits based on the Si5351. This little VFO (34mm by 25mm) consists of the Si5351 ,which is a programmable I2C-Cmos clock generator programmable at any frequency + VCXO support.Also on the board a ATtiny85 ,8 bit microcontroller that runs on 16MHz~20MHz.At the back of the PCB you will find the Rotary Encoder to adjust the frequency.This VFO is a very clever design because the only thing you have to do is drill a 7mm hole in the front of your case and attach the VFO with the mounting ring of the Rotary encoder.The VFO works on 5 Volts and it uses 18 to 24mA.This VFO is programmed in the range of 4.000MHz ~ 4.350MHz for the test with the Bitx20 that has a IF of 10.000MHz.Any other frequency can be programmed for any band or IF.
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When you power up the VFO the start frequency is 14.200 MHz USB.The dial speed of the VFO is 1042Hz X 96 = 100KHz each turn.If you press the Rotary Encoder shortly ,the VFO goes to fine tunning mode.Now we have 26Hz X 96 = 250Hz each turn.When we press the Rotary Encoder for a few seconds,we return to the offset frequency of 14.200MHz again.
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I connected the new Si5351 VFO to my Bitx20 "Dead Bug Style".Before that I had to disconnect the onboard VFO and instead of that I put the output of the new VFO directly on the mixer side of the Bitx20.I also connected a frequency counter for the test.When I turned the power on ,the rig immediately came to life.Several stations where heard and the VFO performes great. Because there are no inductive parts on the VFO,there is no "hand effect"when you turn the dial of the Rotary encoder.When you choose a frequency,it stay`s on it,even after a 3 hour test period the frequency didn`t shift.I also made some QSO`s with the set-up.There was no re-tune needed after I let go of the microphone ,which is needed with the on-board VFO.
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Picture of the set-up.The Bitx20,IK3OIL frequency counter and the Si5351 VFO.Picture below the scematic of the VFO.
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When you power up the VFO the start frequency is 14.200 MHz USB.The dial speed of the VFO is 1042Hz X 96 = 100KHz each turn.If you press the Rotary Encoder shortly ,the VFO goes to fine tunning mode.Now we have 26Hz X 96 = 250Hz each turn.When we press the Rotary Encoder for a few seconds,we return to the offset frequency of 14.200MHz again.
I connected the new Si5351 VFO to my Bitx20 "Dead Bug Style".Before that I had to disconnect the onboard VFO and instead of that I put the output of the new VFO directly on the mixer side of the Bitx20.I also connected a frequency counter for the test.When I turned the power on ,the rig immediately came to life.Several stations where heard and the VFO performes great. Because there are no inductive parts on the VFO,there is no "hand effect"when you turn the dial of the Rotary encoder.When you choose a frequency,it stay`s on it,even after a 3 hour test period the frequency didn`t shift.I also made some QSO`s with the set-up.There was no re-tune needed after I let go of the microphone ,which is needed with the on-board VFO.
Picture of the set-up.The Bitx20,IK3OIL frequency counter and the Si5351 VFO.Picture below the scematic of the VFO.
