Michael Ossmann’s Talk on RF Circuit Design
At the 2015 Hackaday super conference Michael Ossmann (designer of the HackRF SDR and various other RF products) gave a talk called “Simple RF Circuit Design”. His talk explains in very simple terms how to successfully create RF circuits without the need to do any complicated calculations. The workshop blurb reads:
This workshop on Simple RF Circuit Design was presented by Michael Ossmann at the 2015 Hackaday Superconference. It sold out almost immediately and for good reason. He has designed numerous popular tools like the the HackRF One and YARD Stick One. Michael’s depth of knowledge and experience make him a leader in a field that is often called a dark art. There is no reason to fear RF design. Follow his recommendations and remove some of the mystery from the topic.
Essentially his talk boils down to 5 rules:
- Use Four Layers
You’ll have less RF trouble and design work with four layers than on a two layer board. Four layers allows you to have unbroken power planes which helps to reduce ground loops.
- Use the Most Integrated Component Possible
Instead of designing your own RLC circuits and filters and taking into account various factors like Q values, just use an integrated circuited with defined parameters.
- Design for 50 ohms Everywhere
Keep every thing matched to the standard 50 Ohms for optimal impedance matching.
- Follow Manufacturer Recommendations
Use the layouts specified by the manufacturer.
- Route the RF Parts First
Route the most critical part, the RF section first and keep digital lines away.
Number 3 is more important than it may seem but it’s probably the biggest mistake made by the inexperienced in RF design. It makes the different stages “plug and play’ so you can say try a new IF design without having the change the circuits in front or behind it, it makes your filters plug and play also
You also need to make all your test equipment including scope probes/inputs are 50 ohms also and take into account RF is measured as a Power (usually in milliwatts or dBm) and not a Voltage