I use the VK6YSF pages to build my baluns. The instructions are clear and cover all
the parts and building instructions, and the materials are readily available in
1:1 Choking balun Choking balun for lower HF and MF bands. (1.8MHz - 10MHz) T250-26 Powdered Iron Toroid Core..
1:1 Guanella current balun 1:1 Guanella current balun (1.8 - 30MHz) L15 ferrite toroid core.
1:4 Guanella current balun 1:4 Guanella current balun (1.8 - 30MHz) L15 ferrite toroid core.
1:1 Ruthroff voltage balun, 1:1 Ruthroff voltage balun (1.8 - 30MHz) T-200-2 powdered iron toroid core.
4:1 Ruthroff voltage balun 4:1 Ruthroff voltage balun (1.8 - 30MHz) T-200-2 powdered iron toroid core.
6:1 Ruthroff voltage balun 6:1 Ruthroff voltage balun (1.8 - 30MHz) L15 ferrite toroid core.
1:9 voltage unun_v1 9:1 voltage unun (1.8 - 30MHz) T-200-2 powdered iron toroid core. Version 1
1:9 voltage unun_v2 9:1 voltage unun (1.8 - 30MHz) L15 ferrite toroid core. Version 2
9:1 Voltage Balun
Also see Martin Ehrenfried G8JNJ 2007 to 2019 - A disscussion on problem of providing a balanced feed from an un-balanced atu. Martin Ehrenfried G8JNJ 2007 to 2019
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:
An experimental Coaxial Tank V.H.F. (Bandpass) Filter Designer (Cavity) https://www.changpuak.ch/electronics/Coaxial_Tank_VHF_Filter_Designer.php
A Brief Guide to Telewave’s Cavity Filters:
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: