1. Filter Types
  2. QRP Labs' Band Pass Filter kits
  3. Filters Designed for the Rpi
  4. Coils
  5. Telewave Cavity Filters
  6. Cavity Filters
  7. Measuring Cavity Filters with a VNA
  8. Series Combiners
  9. References


Filter Types


QRP Labs' Band Pass Filter kits

QRP Labs' Band Pass Filter kits
QRP Labs' Band Pass Filter kits - HF Filters


Filters Designed for the Rpi

Simple and Effective Lowpass Filters and Amplifier for Raspberry Pi 2 and 3:

A short guide to harmonic filter for QRP transmitter output [PDF]:

RockingD Labs - RF Filter for a Raspberry Pi Transmitter: [Top][Home]

This kit is a daughter board, designed by Jan G0BBL and Tony KB9YIG, that provides four electronically switched band-pass filters for the Softrock Lite + Xtall V9.0 RX, replacing the single-band daughter board in the original design.
HF BPF Project:



How to construct a loading coil for 80m

Coil-Shortened Vertical Antenna Calculator
Coil-Shortened Vertical Antenna Calculator


Telewave Cavity Filters

A Brief Guide to Telewave’s Cavity Filters:


Air Cored Coils

This is a theory based introduction to the air cored coil.



Cavity Filters

Cavity Filters

What is a Cavity Filter?
Resonant cavity filters are used as building blocks in duplexers, pre and post selector filters, and in receiver and transmitter multicoupling configurations. Individual cavities may also be used for a variety of interference management applications.

Amateur Radio Wiki - Explanation of a cavity filter?:

RFI Technology Cavity Filters:

Video - Fun with Cavity Filters:


Measuring Cavity Filters with a VNA


Series Combiners

Series Combiner

What is a Series Combiner?
Band Pass and Series Combiner responses are similar; however the Series Combiner is used specifically to provide two distinct and isolated signal paths. One path from a primary input/output to a common feeder line port, which exhibits a the band pass characteristic centred at the resonant frequency of the cavity and the second path from a secondary input / output port to the common feeder line port behaving as a low loss transmission line at frequencies other than the resonant frequency of the cavity.

RFI Technology Combiners:



An experimental Coaxial Tank V.H.F. (Bandpass) Filter Designer (Cavity)

Glenn Lyons VK4PK
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