Project: Freedom7 HF Transceiver
Component: VFO/BFO (Oscillators)
Status: Assembly (Complete) … Testing begins (Apr 4, 2026)
Update: Assembly complete and smoke-tested. See more towards the end of this posting.
March 24, 2026
I just received my PCBs for my VFO/BFO oscillator factory component. I have all my parts. Now I need to sit at the bench and assemble this dude! Assembly baby!
I almost finished the assembly last night but I missed a resistor and one of my hand-wound coils came off the pad. The magnet wire came with clear enamel. I should have known to look for colored enamel magnet wire. I’ll go over the PCB closely before I begin testing for soldering errors or bridges over the small chip pads.
I’m nervous about this one because the parts were expensive and the PCB was larger. I have 5 PCBs but still each part introduces the possibility of short or disconnection. The testing will take some time too.
3 points if you comment and tell me the part/component I forgot late last night.
I have completed the VFO/BFO, I think lol. I.e. I’ve attached every child component of this parent design and I’ve smoke-tested this new architectural component. I checked the voltage on my drop-down regulators (low-noise, high-quality) and they were not 3.3v.
I think I was given instruction per datasheet to leave pin 7s floating. I cannot recall if this was 1) datasheet or 2) my AI partner. Pin 7 is an Enable (HIGH) and I specifically remember reading that the pin was held HIGH internally.
I have two quality issues with this component and they are both specification issues in the PCB design. PCBWay has done a fantastic job with consistent quality however I am slowing my design with each and every design/drafting session in KiCad.
If you notice in the image above, the terminal block seems misaligned. It is! I think the footprint and the actual terminal block are not correctly matched. The pins for the block are tiny and the pad holes too large. A mechanical engineering failure here has caused the pins to move beneath the terminal with several connect and disconnects of power to the component.
The second quality issue is obviously the need to tie pin 6 (Vin) to pin 7 (enable) as you can see. I could have purposely created a solder bridge, and probably should have done that first, but I didn’t. Now I look at my creation and cringe. This and the terminal block foundations can be fixed with a PCB redesign.
April 4, 2026
Being the confident one, I decided I would begin the real testing with an Arduino sketch (C++) and a male SMA on coax to a BNC into my scope. What a disaster that was! I’m having deja vu now of testing an RF LNA on a white plastic breadboard lol.
I began with the BFO because that’s to be a fixed 9 MHz to sit between the side bands. At the SMA (buffered and filtered), I could not get a stable or triggered response that would hold (cycle). I moved back to the Si5351a and still all over the place. To also add that when the frequency counter was even registering, the MHz varied between 40-60MHz. The first test should be to measure a solid reference clock at the TCXO feeding the Si5351a. Many DIY/Homebrew folks use the little breakout boards that come with the Si5351a. I wanted a little more stability for my VFO or the other output I’ll be discussing soon. For now, my BFO is a fixed frequency from an Si5351a with a TCXO reference 25 MHz.
Check back soon …
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david [at] kr4bad-dot-com
73,
KR4BAD David