Practical RF Filter Design

RF filter design is a piece of cake these days thanks to computer design and simulation tools. But actually realizing the simulated filter response in the real world can be a completely different matter! This video provides an introduction to practical RF filter design by building, testing, and tweaking a 137MHz bandpass filter suitable for NOAA APT satellite reception.

References and additional reading:

Description Reference
Designing a high-Q VHF bandpass filter A VHF Bandpass Filter for the QST Spectrum Analyzer, Wes Hayward, W7ZOI
Enameled wire capacitors Capacitance of a Wire Above a Foil, Wes Hayward, W7ZOI
Tutorial on double tuned bandpass filters The Double-Tuned Filter: An Experimenter’s Tutorial, Wes Hayward, W7ZOI
Air core inductor Q The Elusive Q of Single-Layer Air-Core Coils, George Murphey

3 thoughts on “Practical RF Filter Design

  1. Craig,
    You are a good teacher. It is hard to find one who can explain RF techniques in simple terms.
    Your videos need to reach a larger audience. Every maker space in America should show your video’s.

  2. Good tutorial. My thoughts:
    1. Self-supporting solenoidal inductors like the ones in your video can allow you to eliminate the variable capacitors. Many FM radios and VHF TV tuners use the aforementioned inductors in conjunction with fixed capacitors in order to minimize cost. The filters are then tuned by either compressing or expanding the inductors.
    2. In commercial designs at VHF and above, it is a standard procedure to account for component parasitics and Q factor in the simulation. At microwaves, modeling the parasitics is essential whether commercial or for fun. See the article below:

  3. Pingback: ‘Practical RF Filter Design & Construction’ Video « Adafruit Industries – Makers, hackers, artists, designers and engineers!

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