This builder supports fast failure. Read on … you’ll understand. Or, build on and you’ll understand too.
The first modular component I designed and created was the PCB for seven unique band-pass filters. They are passive and I could use a NanoVNA to actually show the performance curve with the RF spectrum from the NanoVNA device. I have created the front-switching component for these band-pass filters and also a RX/TX switching component. There are many things to test. This post will consider the tools I currently have and the methods I will use with these tools.
I have an inexpensive, but serviceable oscilloscope and a pretty decent smart multimeter. The multimeter can check capacitors, diode forward-voltage, and even temperature. I have breadboards and various power supplies with sufficient amperage needed. I try to prototype and test each unique network task, chip, configuration, digital logic, etc before PCB manufacture. I have LTSpice for circuit modeling. I used LTSpice heavily during my bandpass filter design. I did not model the RX/TX switching schematic.
My first test of the RX/TX switching component was to power it on with 5V and adjust a potentiometer for my 28V biasing (block) against schottky diodes. I powered the module and a small inductor started smoking. Hard stop! I had to completely rethink my design and testing. I should have considered everything prior to making the PCB and choosing components. This was all prior to any real testing.
My lesson learned here is to consider amperage in all cases. And while I’m very excited with these SMD components, again I need to pay attention to voltage, amperage, wattage, etc. or component rating basically. My RX/TX switching component is pretty solid design on the receive side because the RF power is nothing really. The transmitting side completely forgot the RF power it would see. I really need an interface between the transmitting side and the central antenna connector.
I also learned that I need a signal generator. I need a unique fixed RF frequency to send through components. I have a NanoVNA and I’ve been told that it can emit fixed frequencies. I will learn about the NanoVNA or I will make a testing signal generator using the Si5351a that I will use for my VFO.
I’m trying to make ultimate use of the tools that I have. This radio project has been expensive. I need to use my head for something besides a hat-rack like my Dad always said. I think I have what I need to get me through most of what I need to test but that means, more focus on design. I also need to write down my tests regardless of simplicity.
In conclusion, I’ve determined that more effort is needed before schematic, component, and PCB acceptance. Every circuit that isn’t completely clear in my mind should be modeled if possible in LTSpice. And, the component BOMs should be scrutinized for ratings, specs, etc. beyond just PCB footprint. More of everything needs to be written down.
“Support fast failures” … Tom Peters
My About page provides the background of my project, the Freedom7 HF Transceiver.
If this story resonates, comments are welcome. You can also reach me at david [at] kr4bad-dot-communications. no com
And if you believe understanding matters more than black boxes, you can subscribe to my WordPress https://kr4bad.com/?subscribe=1.
73 KR4BAD David
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