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This is an interactive design package for designing analogue (i.e. hardware) filters made of inductors and capacitors (Ls and Cs).

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.

A re-usable control & computing platform for antenna measurement, PSK31 digital modems, audio filtering, signal source & VFO, memory keyer by AMQRP

Operating a specialized DX cluster, this service provides real-time DX spots exclusively from stations confirmed to be _Log of The World_ (LoTW) users. This unique filtering mechanism allows DXers to prioritize contacts with stations that are highly likely to upload their logs to LoTW, streamlining the process of achieving confirmed DXCC or other awards. The cluster aggregates data from various sources, presenting a focused view of active LoTW participants across multiple bands. By narrowing the scope to LoTW-active stations, the platform significantly reduces the effort required for QSL management, as users can confidently pursue contacts knowing a digital confirmation is probable. This targeted approach is particularly beneficial for contesters and DXpedition chasers aiming for rapid award qualification, offering a strategic advantage in identifying viable contacts. The service supports both web-based access and traditional telnet connections, ensuring broad compatibility for amateur radio operators. It processes thousands of spots daily, with a focus on delivering accurate and timely information relevant to LoTW users, facilitating more efficient and productive operating sessions.

Manufacturer of single band and multiband transceiver bandpass filters for HF. High pass filters, two radoi headphones mix and switch, 6 meter portable antenna, antenna remote switching and steering.

Dedicated to State-of-the-Art lightweight portable radio. Sotabeams produces and sells amateur radio products dedicated to ham radio portable operations. Antennas, supports and masts, filters, wires and more accessories for amateur radio.

This circuit consists of microphone amplifier and a high pass filter. Suitable to improve signal readability.

Suppressing noises from your plasma TV or other unwanted signal sources

A ATU for beam and vertical antennas by PA0FRI

This page describes a fix to the Low Pass Filter that provides more filtering of the second harmonic of 144-148 MHz.

Alk engineering - filter design software and consulting

Part 2 You're now much closer to saying goodbye to your unwanted signal problems!

The 2.1 kHz wide European LF allocation between 135.7 and 137.8 kHz is detailed in this observed band plan, offering guidance for activity within this narrow segment. It specifically addresses the challenge of locating weak signals, such as those from Slow-CW stations, which can have bandwidths of only a few Hertz. The resource emphasizes the utility of precise frequency knowledge when operating with narrow DSP filters, like a 30 Hz filter for CW, to differentiate multiple stations within a very small band segment. The plan, though not officially recognized, provides practical orientation for operators, particularly those new to the _LF band_. It references a similar plan published by the _RSGB_ in the January 2000 issue of _RADCOM_, suggesting a community-driven approach to band organization. The content highlights the importance of spectral awareness, noting that multiple stations can occupy minimal bandwidth, a concept illustrated by spectrographic analysis.

The Super Check Partial database files provide a list of callsigns used by active contesters. The data comes from Cabrillo logs contributed by contesters themselves. Contributed logs from the past 24 months are used to create the database. These logs are combined and filtered so that they result in a fairly good (but not perfect) list. The files do not contain any QSO data, such as state, CQ zone, Maidenhead Grid Locator, etc. The dta files can be used with CT, WriteLog, TRlog, SD, N1MM Logger, NA, Win-Test, and others

RFAC Solutions specializes in providing a range of RF components, including various connector types, cable assemblies, attenuators, and filters. Their product line features common connector standards such as SMA, BNC, TNC, N-Type, MCX, and MMCX, essential for reliable RF signal paths in amateur radio and commercial applications. The company also offers high-power VHF amplifiers, catering to needs for signal boosting in specific frequency ranges. Their offerings extend to dust caps and adapters, which are crucial for maintaining the integrity and versatility of RF systems. The focus on supplying components from South Korea suggests a commitment to specific manufacturing standards and supply chain practices. This resource details a vendor's product scope, useful for hams sourcing specific parts for shack builds or antenna projects. Jeff is listed as a contact for inquiries.

A range of easy-to-build RFI filters by John Regnault, G4SWX

UK manufacturer of ham radio accessories, including TNX, SDR receivers, RF Diplexers Triplexers, bandpass filters, iambic memory keyers.

Radio frequency systems require robust protection against transient voltage events, which can severely damage sensitive equipment. This resource details a range of **RF surge protection** devices, including models with DC Pass, DC Block, Bias T, and Ultra Low PIM characteristics, designed to safeguard critical infrastructure. It also presents various RF filtering solutions and interconnect components, emphasizing their role in maintaining signal integrity and operational continuity across diverse applications. The site provides information on products engineered for both RF and data line protection, highlighting their utility in preventing downtime and equipment loss. Specific product categories encompass coaxial protectors, grounding items, and fiber optic solutions, indicating a broad scope of application from amateur radio installations to industrial and telecommunications networks. Furthermore, the resource mentions the availability of NOM-certified products and offers same-day shipping for many items, underscoring a commitment to rapid deployment and compliance with industry standards.

Industrial Communication Engineers (ICE) was a manufacturer specializing in **RF components** and solutions for amateur radio and commercial applications. Their product line included a range of RF parts, various types of filters, and RF switching products designed to enhance station performance and mitigate interference. These components were critical for hams engaged in contesting, DXing, or general operating, providing means to improve signal integrity and manage complex antenna systems. The company's offerings addressed common operational challenges such as RFI and TVI, with products like **low pass filters** and antenna filters. While the specific technical specifications of their product range are no longer available, such components typically provided significant attenuation of unwanted harmonics and out-of-band emissions, crucial for maintaining a clean signal and preventing interference with other electronic devices. The current status indicates the domain is for sale, suggesting the manufacturing operations have ceased.

Maker of QRP Kits, QRP CW receiver and transmitters, audio CW Filters, antenna tuners, dummy loads, and morse code practice oscillator

A 4 AMP / 18V regulated power supply schematic, designed by _ON6MU_, provides a detailed circuit diagram for constructing a robust power source. The design focuses on delivering a stable 18-volt output at up to 4 amperes, crucial for powering various amateur radio equipment. This resource presents a clear visual representation of component interconnections, including rectifiers, filter capacitors, and voltage regulation stages, essential for DIY enthusiasts building their shack infrastructure. The schematic's clarity facilitates understanding the power flow and component roles within the circuit. This circuit design offers a practical solution for hams needing a reliable 18V supply, potentially useful for driving specific transceivers, amplifiers, or accessory circuits. While specific performance measurements or comparisons to other designs are not detailed, the schematic itself serves as a foundational blueprint. Builders can adapt or modify the _power supply_ to suit their particular needs, such as integrating overcurrent protection or fine-tuning the output voltage with adjustable regulators. The straightforward presentation makes it accessible for those with basic electronics knowledge to assemble and troubleshoot.

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.

Yaesu FT-2000 roofing filters

Diplexer is a passive device, a special filter circuit that seperates 2 different bands, not to be confused with the duplexer that usually separate 2 different frequencies on the same band.

Presents a QRP AM/CW transmitter project specifically designed for the 10-meter band, utilizing a crystal oscillator and a collector-modulated AM oscillator. The design employs a 2N2219(A) transistor in a Colpitts configuration, generating 100 to 350 mW of RF output power depending on the 9-18 Volt supply voltage and modulation depth. Frequency stability is maintained by a 28 MHz crystal, with fine-tuning possible via a Ct1 trimmer capacitor for approximately 1 kHz adjustment. The resource details the RF oscillator stage, implemented with a 2N2219 NPN transistor, emphasizing frequency stability and low power dissipation. It also covers the amplitude modulation stage, managed by a 2N2905 PNP transistor, which impresses audio information onto the carrier. Selective components (C3, C4, C7, C5) enhance voice frequencies within a +/- 5 kHz bandwidth, and modulation depth is controlled by R2 and R3. The project includes a 3-element L-type narrow bandpass filter (Ct3, L3, C10) to suppress harmonics and ensure a clean output signal. The project provides a complete schematic diagram, a comprehensive parts list including specific capacitor, resistor, and inductor values, and construction notes for the coils (L1, L2, L3). It also offers practical advice on enclosure requirements, suggesting an all-metal case or a PVC box with graphite paint for RF shielding. Operational parameters such as current draw (27mA@9V to 45mA@16V) and input impedance (50 Ohms) are specified, alongside guidance on antenna matching and the importance of a valid amateur radio license for 10-meter band operation.

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

Demonstrates how to construct an automatic band decoder, moving beyond manual selector switches for antenna and filter control. It addresses the challenge of varying band data outputs from different transceivers: Icom rigs provide voltage values, Yaesu rigs use Binary Coded Decimal (BCD), and Kenwood rigs lack direct band data output. The resource highlights a clever solution utilizing logging software like _CT (K1EA)_ and _DX4WIN_ to emulate Yaesu's BCD output via a PC's printer port, making the decoder compatible with any rig. The author details experiences building decoders based on designs by Bob _K6XX_ and Guy _ON4AOI_, noting K6XX's simple TTL chip design and ON4AOI's more comprehensive, opto-isolated unit capable of controlling ten outputs and bandpass filters like the _Dunestar_. It also references a _W9XT_ board design, which Steve Wilson, G3VMW, modified with BD140 transistors for source drivers, emphasizing safety. The author successfully cased an ON4AOI-based decoder in an old modem case, connecting it to an FT1000MP or a PC printer port to drive remote relays and a Dunestar Band Pass Filter.

Filter design software. A program designed to expedite the design and analysis of lowpass (and highpass) filters with nearest 5% component values. SVCfilter is 32-bit Windows electrical filter design software nicely written to help the radio amateur, technician or engineer design and analyze lumped-element lowpass and highpass filters.

A homemade tunable bandpass filter for all HF bands from 160m to 10m

The Rock-Mite is a 40m CW kit offered by Small Wonder Labs . It features built-in keyer, direct conversion receiver with a crystal RF bandpass filter, 500 milliwatts of power, and switchable frequency offsets to work around QRM

Sherwood Engineering Inc. (SEI) offers a repository of technical presentations and white papers focused on optimizing amateur radio transceiver and receiver performance. Content includes detailed analyses of _roofing filters_, transmitted IMD, and receiver characteristics, with specific discussions on products like the Drake R-4C and Icom IC-781. Presentations from events such as Dayton Contest University (2008-2014) cover topics like "How To Optimize Rig Performance," "Transceiver Performance: 10 Years of Change," and "Choosing a Transceiver: Far from Simple." Additional white papers address HF mobile antenna efficiency, ground screen alternatives to buried radial systems, and common receiver problems with solutions. The site also provides historical product information for items like the SE-3 MK IV synchronous AM detector and various 455 kHz mechanical and crystal filters, though many products are no longer in production. Receiver test data and alignment tips for the R-4C are also available, offering insights into rig modifications and performance enhancements.

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

A home made antenna tuner based on the W6JJZ basic concept that ,atches balanced loads without the use of lossy baluns, can provide band-pass filtering and harmonic attenuation.

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

GQRX is a free and simple to use SDR receiver which runs on Linux and MacOS X. GQRX comes with a standard FFT spectrum and waterfall display and a number of common filter settings

Coaxial stub filters used at W7GJ

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

Project of receive only filters optimized for minimal loss and very high rejection of frequencies below 75% of the filter center frequency by K1TTT

The Yaesu FT-1000MP Mark-V, introduced at Dayton 2000 Hamvention, features a higher RF power of **200 W PEP** and a Class-A amplification SSB mode at 75 W. Key enhancements include an _Interlocked Digital/Analog Bandwidth Tracking system (IDBT)_, a Variable Front-End Filter (VRF) preselector, and improved ergonomics, notably a multi-function shuttle jog dial. This model, a successor to the 1996 FT-1000 and FT-1000MP, was designed to compete with high-end transceivers, despite its retail price of $4200 initially. The transceiver's physical dimensions are 406 x 135 x 348 mm (16 x 5.3 x 13.7 inches) with a weight of 14 kg (31 lbs), making it substantial. Its rear panel offers over 20 connections, including power, external DSP speaker, BAND DATA I/O, ALC, and multiple interface jacks for DVS-2, Packet, and RTTY. The unit also provides two keyer inputs, a DB9M serial interface for CAT, and two PL female antenna connectors, plus additional receive antenna jacks. Despite its advanced internal architecture, including two independent receivers with their own IF filters and AGC loops, the display technology, utilizing fluorescent discharge rather than LCD, contributes to an older aesthetic. The control panel is extensive, featuring 92 knobs and buttons, alongside numerous LED indicators for various modes and functions.

Project to build sets of band pass transmitting filters for reducing the interference between HF transceivers operated in close proximity

The County Hunting software, version **6.1**, is designed for amateur radio operators focused on USA-CA Award tracking and logging. This application supports _Windows_ environments and facilitates the import and export of ADIF files, enhancing QSL management by integrating electronic confirmations via LoTW and e-QSL. The software has been updated to align with the new award rules managed by MARAC, following the discontinuation of CQ magazine's involvement. Users can visualize QSLs post-scanning and benefit from enhanced ADIF import functionality. Version 5.4 introduced accelerated county searches via FCC databases, with filters for QSL confirmations and e-QSL enhancements. The software also includes a feature for backing up and restoring QSOs by LoTW confirmations. Visual County tools have been refined, offering improved map interactions and the addition of county flags. The software supports various digital modes including FT8, FT4, and SSTV, and includes functionality for PSK250 and 60m bands. The application is multilingual, with support for Italian, English, French, and Spanish, and provides automated updates and web-based county searches. DXZone Focus: County Hunting | ADIF | Windows | LoTW

The resource details the construction of a homebrew 50-watt FET amplifier, based on Don W6JL's _QST Homebrew contest_-winning design from 2009. It functions as an afterburner for QRP transceivers, providing a **12dB** power lift. The amplifier utilizes IRFZ24N FETs and covers the 80, 40, 30, and 20-meter bands, with the 20m LPF extending to 17m. Key technical aspects include an FT37-43 transformer for the input network, a relay-switched 3dB pad for lower bands controlled by an _Arduino Nano_, and an RF-actuated T/R switch. The LPF board integrates four relay-switched filters rated for 50 watts, using capacitors with a minimum 250VDC rating. Performance measurements indicate a power gain ranging from **4.4dB** on 20m to 8.1dB on 80m, with a required drive power of approximately 5 watts. The article also discusses thermal management, current limiting considerations, and component sourcing.

High pass filter schematics for TVI and examples of finished filters

A K9AY loop antenna project done with Far Circuits pc boards for the antenna switch and bandpass filter and preamp by K7SFN

This is an interactive filter design package, for designing digital filters

The HotPaw Morse Code Decoder application for macOS processes audio input to transcribe Morse code characters into text. It presents both an audio spectrum graph and a tone amplitude graph, which aid in configuring a narrow band audio filter. Operators can set the audio filter for tone frequencies between 400 and 1600 Hz, optimizing reception for various CW signals. The software offers user-configurable settings, including WPM dot/dash speed detection, a noise threshold level, and the option to use Farnsworth timing for inter-character spacing. The Morse code WPM detection automatically adapts from approximately 8 to 40 WPM, with a lock feature for the estimated speed. A High Speed WPM Mode is available for code speeds ranging from 40 to 80 WPM, catering to faster CW operators. The application's decoding performance is influenced by signal level, signal-to-noise ratio, frequency and WPM stability, keying quality, and proper configuration, with an initial learning phase required for WPM estimation to stabilize. An external microphone or line-in may be necessary for optimal performance on some MacBook models to mitigate fan noise or room reverberations. Version 1.4.4, updated on November 11, 2021, includes compatibility improvements for newer macOS releases. The developer, Ronald Nicholson of HotPaw Productions, does not collect any user data from the application.

International crystal manufacturing provides quartz crystals, oscillators, precision crystals, filters, tcxos / vctcxos, qcm crystals, and other frequency control products. read details about our crystals and frequency control products and services.

An improved version of DK9NL QRM Killer, with dedicated noise sampling antenna for completely filtering of plasma TV rattle on HF bands

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

Taking the venerable SMK-1 design to 20m and adding an RF amp, audio filter, and a TiCK Keyer ... by Wayne McFee, NB6M