RF Filters for Amateur Radio Operators
Find resources for designing, building, and implementing various RF filters to improve signal quality and reduce interference in your ham shack.
Filters are essential in ham radio to manage interference, improve receiver performance, and ensure clean signals. Operators use various types of filters to mitigate RFI and TVI, protect sensitive receiver front ends, and enhance the clarity of desired signals on crowded bands. Effective filtering is crucial for both single-operator stations and multi-operator contest environments where multiple transceivers operate in close proximity.
This category provides resources for understanding and building filters, from simple mains filters using ferrite cores to complex multi-band receive filters. Hams can find guides on using ferrite for interference suppression, design tools for LC filters and interdigital bandpass filters, and projects like the NVARC Ugly Filter. There are also articles detailing specific installations, such as adding an Inrad roofing filter to a Yaesu FT-920 or improving the DSP filtering in an Icom IC-775, helping operators optimize their stations for better QSOs.
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This is an interactive filter design package, for designing digital filters -
A homemade band pass filter for the 30 meter band based on the original VE7BPO design -
Sometimes many VHF-UHF modern transceivers have problems with BROADCAST Interference and CROSS-modulation from FM commercial broadcast stations this article shows a simple Batteworth HI-Pass VHF Filter to reduce this problem -
An home made low pass filter for 70 MHz by IK0VAQ -
High speed silicn diodes work well as RF switches. This article describes how to use diodes for selecting two or more filters ARRL QST article by W1FB -
Do your multiple-transmitter field day or contest efforts suffer from intrastation interference ? -
These inexpensive, easily built filters can be the buffer you need between the signals you want to hear and send and those you don't! -
Part 2 You're now much closer to saying goodbye to your unwanted signal problems! -
Coaxial stub filters used at W7GJ -
A range of easy-to-build RFI filters by John Regnault, G4SWX -
The document is a technical guide on designing RF filters for radio frequency applications. It covers topics such as interference suppression, band-pass filters, and low pass filters, with a focus on filter design and circuit filters. -
Replacing filters on ICOM IC 775 -
This article is about the characteristics and use of various filters and ferrites for solving amateur radio electromagnetic compatibility problems involving breakthrough of amateur signals into domestic equipment such as television sets, video recorders stereo sytems etc. -
Understand how high pass filters are done -
Online calculator and design aid for 2nd order active low-pass and high-pass filters, providing component values based on equations or tables. -
An home-brewed morse code CW filter with a central frequency of 800hz and a variable bandwidth from 230hz to 26hz by F5RDH in french. -
Article showing how I've made a mains filter to reduce EMC in the electricity supplying my shack. I've used a type 31 Fair-Rite ferrite core and the video shows how this performs on 160m through to 40m. -
Fill out the form to design a bandpass filter as described in the January 1985 issue of Ham Radio Magazine. These filters are generally limited to frequencies above 200 MHZ because their size is slightly longer than 1/4 wavelength -
The page provides detailed information on coax stub filters for multi-transmitter setups, including specific lengths for different bands and types of coax. It also references additional technical notes for further analysis. -
The QLF filter is a microprocessor based interface designed to go between a standard Morse code key and a radio transmitter -
This is an interactive design package for designing analogue (i.e. hardware) filters made of inductors and capacitors (Ls and Cs). -
Article explaining electronic network of low pass filters -
Javascript filter design page with introduction to low pass filters by k7mem -
This type of filter can be used in a Mode J satellite station (uplink on 2m, downlink on 70cm) to reduce the problem of the uplink signal desensing the receiver -
Band-pass filters can be critical components in competitive stations. This setup may help put your station on the map. -
This site is dedicated to design and analysis of micro- and millimeter wave filters from 0.5 to above 100 GHz. -
Sometimes we need a little more output filtering than traditional designs offer. Look at a new filter that can give you that extra boost. QST article by W3NQN -
A pdf file with schematics of an ssb and cw filter AF amplifier -
Project to build sets of band pass transmitting filters for reducing the interference between HF transceivers operated in close proximity -
A homemade tunable bandpass filter for all HF bands from 160m to 10m -
Clean Up Your Signals with Band-Pass Filters -
Excellent guide to using ferrite cores for interference suppression. Understanding and Solving RF Interference and Noise Problems by Jim Brown K9YC Audio Systems Group, Inc. PDF File -
As the sunspots return and DX propagation conditions to improve, the age old problem with QRM begins to show up on the amateur bands. Thif filter help you on improving reception -
VHF Broadcast Passband Filter (88 108 MHz) by DF9CY -
Project of receive only filters optimized for minimal loss and very high rejection of frequencies below 75% of the filter center frequency by K1TTT -
This is a 6 band receive only filter designed to protect your receiver front end and provide 45dB reject at the stop bands. This is a 6-band receive only filter designed to protect your receiver front end and provide 45dB reject at the stop bands. Stop band reject may be limited by the relay isolation. Worse case isolation is at 28 MHz or 35 dB or better. Relay K3/K8 protects the filter during transmit via the PTT line. A 25-50ms delay must be used between transmit and PTT. Do not rely on your radio to provide adequate delay with out using the PTT. You logging software must be set to allow a delay between PTT and time of 1st transmit. This filter will not work with VOX or QSK keying as you will damage the filter. -
A combined 144MHz Low-Pass and 432 MHz Notch Filter by VE2ZAZ -
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. -
2 filter designs a 3-pole and a 5-pole -
Combined 432 MHz High-Pass - 144 MHz Notch Filter By Bertrand Zauhar, VE2ZAZ -
Homebrew Amateur Radio 440Mhz Interdigital Bandpass Filter -
This low pass filter terminates all harmonics from the 2nd to above the 10th harmonic in a better than 15 db return loss load -
Cavity is often required at a busy site to not only prevent its receiver from being overloaded by off-frequency signals, but also be a good neighbour and prevent low-level signals from your transmitter from getting into other users receivers - not to mention the preventing of those other signal from getting back into your transmitter to generate spurious signals in its own right. -
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. -
This unit uses four capacitors, only two of which are variables, and a single tapped coil. It is built in a die-cast box, and has been tested up to 80W input power on 70MHz by G4CJZ -
Explains cavity filters, their function as sharply tuned resonant circuits, and their role in duplexers for isolating specific frequencies. -
An home madek Audio CW Filter made simply using SMD Components -
If your multiple transceiver station is suffering of intrastation interference, this handy and inexpensive band pass filters and help you. QST article Sept 1988 -
Wikipedia page on Notch filter, a narrow stopband - high Q factor filter -
A simple project for an effective home made band pass filter, designed for the portable field day usage -
How to design narrowband bandpass filters -
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. -
This project involved designing a 7-pole Chebychev broadcast band filter to address severe interference issues caused by a new horizontal loop antenna on the KN-Q7A transceiver. The interference overwhelmed the transceiver’s front end, so a custom filter with a 3.5 MHz cutoff was built using silver mica capacitors and type 6 T130 toroidal cores. Encased in a diecast box with SO239 sockets, the filter blocks strong signals from the broadcast band, achieving over 100 dB attenuation. Tested up to 100W, it reduces interference effectively while maintaining low insertion loss across HF bands. -
This project documents the construction of a coaxial 50 MHz notch filter to eliminate inter-band interference between 50 and 70 MHz transceivers. Using RG-213 coax and based on quarter-wave stubs, the filter achieved a 44 dB attenuation at 50.060 MHz while maintaining low insertion loss on 70 MHz. A dual-stub design broadened the notch response and minimized attenuation on 70 MHz to 0.2 dB. Fine-tuned using an FA-NWT network tester and Elecraft XG3 signal source, the filter effectively resolved interference for seamless dual-band operation. -
Detailed construction guide for an economical 4.433 MHz SSB ladder crystal filter, achieving a 2.2 KHz bandwidth and 2 dB ripple. -
Online Constant - k Lowpass Filter calculator -
How to create a low pass filter able to reduce or even remove the noise generated from your car or truck alternator -
Homebrew CW notch filter project by KN9B -
This webpage caters to EMRFD owners, offering insights into building popcorn receiver band-pass filters with Ladpac programs and EMRFD Chapter 3 knowledge. Through practical experiments and Ladpac tools, the author explores coupling capacitors' impact on filter response and return loss optimization. The content emphasizes empirical approaches, encouraging builders to embrace experimentation and learn from mistakes. Detailed examples and workflow suggestions aid hobbyist-level designers in creating customized filters, fostering a deeper understanding of filter design principles. -
This PDF article introduces a series of dual-tuned bandpass filters designed for input tuning in amateur band receivers. Developed by Stefen Niewiadomski, these filters feature 50-ohm input/output impedance and can be cascaded for improved roll-off outside the passband. The designs use readily available TOKO coils, with taps on the tuned winding for matching input circuits with impedances around 1k ohm. The inductors are core-tuned, with average inductance values provided for easier matching to other inductors. -
This article explores the nuanced design challenges of Band Pass Filters (BPF) in radio receivers, balancing low insertion loss, high stop band rejection, and narrow bandwidth. The focus is on the "Series-Trap, Shunt-C" topology, resonator count impact, and meticulous layout design for superior stop band performance across various frequency bands -
Butterworth Highpass Filter Designer -
Desgining crystal filters and find out crystal data by measuring it. -
Inrad Roofing Filter installation instruction, The IC-775 Roofing Filter Mod consists of a 6 pole, 5 kHz wide filter followed by a high dynamic range, feedback amplifier. -
Learn how to enhance your 160 meter reception by building and using a custom band pass filter. Discover how this filter can reduce interference from strong AM broadcast signals, improving the overall performance of your receiver. Find out about the challenges of creating a filter that balances signal loss and attenuation at specific frequencies, and how it can benefit hams operating near powerful transmitters. Whether you're experiencing IMD issues or looking to optimize your 160 meter setup, this article provides practical insights and solutions for ham radio operators. -
This page discusses the construction and use of a low pass filter for MF/LF reception, specifically for the 630 meter and 2200 meter bands. The author, KA7OEI, shares technical insights and practical advice related to amateur radio, with a focus on improving reception in the low-frequency bands. This resource is useful for hams interested in building their own filters to enhance their MF/LF reception capabilities. -
30m lowpass filter for the Softrock Ensemble RXTX tranceiver. -
This article shows how to make a mains filter that can be extremely effective in reducing and in some cases eliminating completely EMC from the electricity supplying your shack -
Noise bridge circuit to tune your tuner -
Online calculator, Butterworth Bandstop (Notch) Filter Designer -
Offer performance comparable to tin-box filters, and except for being bigger, stack up pretty well with those expensive little helical jobs. You just have to be able to make your own PC boards. -
The website offers technical musings related to amateur radio, with a focus on measuring insertion loss and checking matching. It provides insights and tips for ham radio operators looking to analyze RF devices and circuits effectively. -
an overview, introduction or tutorial about the basics of electronics filters including the types of filter and the various filter design considerations and parameters -
Cutting out the noise using a simple coax filter to improve the poor front end filtering -
SAT filters ensure effective full-duplex satellite QSOs by mitigating interference between 145 MHz uplink and 435 MHz downlink signals. Custom coaxial and SMD-based filters address transmitter harmonic interference and improve receiver isolation, achieving over 70 dB suppression in the undesired band. Designed for simplicity, these filters maintain optimal VSWR and are housed in shielded brass enclosures. Practical implementations with Yagi antennas demonstrate compatibility with SDR systems, enabling seamless communication even in challenging satellite conditions, such as low-elevation passes and DX pile-ups. -
A simple TVI Filter schematic -
The article discusses the construction of a UHF band-stop stub filter to protect an APRS receiver from potential damage during a balloon launch. The author, who communicates using a 441 MHz transmitter, needed to ensure that the RTL-SDR dongle receiving at 144 MHz wouldn't be damaged by the transmissions. The solution involved creating a quarter-wavelength open stub filter using coaxial cable, which attenuates the 441 MHz signal while allowing the 144 MHz signal to pass through. The filter's design is based on the principles of constructive and destructive interference, with careful measurement and trimming to achieve the desired frequency response. The final filter provided 34.8 dB of insertion loss at 441 MHz and minimal loss at 144 MHz, effectively protecting the receiver. -
Building the W3NQN bandpass filters -
The FF-501DX LPF, a high-performance VHF and 10m filter, was obtained at a friend's SK sale. After becoming more active on 10m, the author reexamined the LPF and discovered it to be of high quality. The filter's efficiency was outstanding and the return loss/VSWR was better than estimated. The LPF was connected to a Bird 50R dummy load to evaluate insert loss, cutoff, attenuation over 70MHz, and return loss. The original specifications were found in an old radio magazine, along with a link to the original one-page information sheet. Comparing the results to the original specs confirms the LPF's quality.
