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Third-order Cauer filters can boost performance of multi-transmitter, multi-operator contest stations to the next level. The filters are practical and you don’t need expensive test equipment to align them.

Tips on winding wire coils used as inductive loads, traps, band-pass filters, are implemented in a number of amateur radio projects especially antenna projects

Australia's largest range of Electronic Kits & Components In Stock for the Radio Experimenter, ATV, microwaves, HF Band pass filters

A simple project for an effective home made band pass filter, designed for the portable field day usage

How to design narrowband bandpass filters

Online calculator, Butterworth Bandstop (Notch) Filter Designer

Clean Up Your Signals with Band-Pass Filters, a two-parts article published in this PDF file from a June 1998 QST article

This sweeper built for a narrow bandwidth filter adjustment, use a simple 555 version sawtooth wave generator.

ScopeIIR: an Infinite Impulse Response (IIR) digital filter design tool for Windows. It designs high-order IIR filters based on analog filter prototypes, and can design lowpass, highpass, bandpass, and bandstop filters.

The direct conversion receiver described consists of only a bandpass filter, mixer IC, VFO and audio filter. With only 22 parts, this simple circuit should take a few hours at the weekend to construct.

A High pass filter will not help, use a stop-band filter to notch out the beast.

Clean Up Your Signals with Band-Pass Filters

HF receiving systems and components, band pass filters, array controllers, HI-Z pre amplifiers

Will additional coax stubs improve Band Pass Filter performance?

Build a set of W3NQN filters for multi-operator contesting

Last 15 minute Reverse Beacon Network spots on live graph, let you filter by dx spot continent or spotter continent, as well as by band and let you reduce bandwidth

Filters for the commercial 2 way market, MATV, FM broadcast, laboratory, marine industry, amateur radio, scanner and short wave. Antenna for amateur radio bands

Band pass filters, for radio frequency interference problems.

A homemade band pass filter for the 30 meter band based on the original VE7BPO design

HF Radio Preselectors,BCB filters,Low Pass filters,Band Pass filter

VHF Broadcast Passband Filter (88 108 MHz) by DF9CY

Homebrew Amateur Radio 440Mhz Interdigital Bandpass Filter

Online world map with live updates from the DX Cluster network, displaying new spots on the maps as they appear. Filtering options are available including bands, source continent and dx continent.

Broadband instruments, R and microwave components and filters, field analyzers, spectrum analyzers

Hand made RF sweeper made to adjust the pass band of crystal filter

Passive Band-Pass Filter, low-pass filter calculator

These are QRP rated 3 Pole Butterworth filters based on a design by K4VX, feature simplicity, almost no insertion loss, and reasonable rejection on the other ham bands.

Multi transmitter filters for HF Bands

R3KBO is an amateur radio club producing and developing amateur radio kits and assembled products including HF VHF Power Amplifiers or RF Power Kits and amplifier parts, low pass filfers, band pass filters, sourge protections, splitters and combiners, antenna switches

The program can be used to calculate inductors (coils) and their number of turns on ferrite cores, ferrite shells and air coils. These can be used for baluns, Ununs, bandpass filters, low pass filters, resonant circuits, and more. The technical specifications of the cores are already integrated in the program. Application is free and runs on Windows 32 bit versions only. To make it run on Windows 10 64 bit need to be unzipped in a single folder.

Adding a 20m band pass filter for the Icom IC-706MkII(G) by ON7EQ

An economical way of building an SSB filter. The circuit is for a filter with a 6 DB band width of roughly 2.2 KHz.

Band filters for PA6Z made by PA9M, designed by W3NQN.

Build this circuit to tailor your microphone response to different band conditions. A project by KG4JJH

Homemade LC Bandpass Filters for 20M, 30M, 40M In multi-station environments like special events, field day, portable operating, is very important to protect receivers from excessively strong signals. Bandpass filters help to protect your transceivers.

Wikipedia page on Notch filter, a narrow stopband - high Q factor filter

Building the W3NQN bandpass filters

Upload an ADIF fiel and plot all worked grids in an online map. Support filtering by band, year and can export the output directly into a google map, or a google earth KML file

A complete guide on using the HF amateur radio bands, and the differences with VHF, using filters, influence of solar weather, the split mode and phonetic alphabets.

Antuino is an accurate instrument that can be used in the field to measure SWR, field strength, modulation, etc. In the lab, it can be used to sweep filters, measure gain, distortion, frequency response, etc. It works upto 150 Mhz. On the third harmonic, it is usable on 435 Mhz band as well (with reduced sensitivity).

Thsi article describes a microcontroller driven semi-automatic antenna tuner capable of handling power levels up to 150 watts. The device is a low pass filter tuner manually tuned by setting the optimized L/C combination by hand and then storing the values into the EEPROM of the mictrocontroller to recall them later (seperately for each band from 80 to 10 meters including WARC bands)

Anatech Electronics manufactures RF filters for communication systems, Military and commercial, as well as RF filters for Wireless applications. Products include, Band pass filters, Duplexers, Low pass, high pass and bandstop filters. Additional products such as RF cable assembly also available.

This is the official App of the popular DX Web Cluster DXWatch. You can follow amateur radio DX spots trough the world wide DX cluster network filter by band. Available for iPhone and iPad

These band filters are based on 3 or 5 sections Butterworth band pass filters, maintaining 50 Ohm impedance, and when built around toroidal inductors, can be made very compact.

Elecraft K2 mod. Narrower bandpass filter, better stopband attenuation

HyEnd is a dutch amateur radio antenna manufacturer. Makers of the popular HyEndFeed Antennas, produce Baluns, bandpass filters and selle Line isolators, coax cables and connectors.

Telnet client for DXCluster, Sorts, colours and filters DX Spots by (2) bands, wanted DX Station, who spotted the DX, local to your area and more, Can spot automatically after logging a contact if you are using ZCZ Log, Look up call on QRZ.com

Passive Bandpass Filter online calculator and filter formulas. Active Inverting Op Amp Bandpass Filters, Active Noninverting Op Amp Bandpass Filter, just enter the Low ir High Cutoff Frequency

Utilizing snap-on ferrite cores and practical insights, the author enhances their shack's cleanliness against electromagnetic interference. With meticulous experimentation and installation, they improve noise levels across HF bands, reflecting on the effectiveness of their filter in minimizing common-mode disturbances. Updates underscore ongoing refinement and cautionary advice for optimal filtering and radio reception amid changing RF environments.

Home made 40 meter transceiver project. The receiver is a Progressive Receiver with a few modifications. The Transmitter is a modified MFJ Cub circuit. Includes schematic and circuit diagrams for Receive Input Filter, 3-Pole 500 Hz Cohn Filter and 7 MHz Double Tuned Bandpass Filter