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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

This multiband transverter project features power output at 13,8V 50MHz 15W, 70MHz 10W, second harmonic < 65dBc. Single N connector of antenna, suitable for a dual band Yagi. Article include Block Diagram for Dual Transverter and low pass filters

1-watt 17-meter cw transmitter that was originally done about 10 years ago as a club project for RAMS, the Radio Amateur Megacycle Society. It uses a VXO, rather novel at the time. It also uses a bandpass filter at the output rather than the usual lowpass

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.

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.

Contest log checker to detect QSO band passes. The PASS program reads a Cabrillo log and reports the QSOs that were passed (moved) from one band to another. The program is not graphical and it is meant to be run at a DOS prompt or in a CMD window under Windows.

Custom built high and low power power band pass Filters, low band triplexers, triplexers and diplexers

This project introduces the Loggi, a hybrid antenna merging the wide frequency coverage of log-periodic dipole arrays (LPDA) with the high gain and front-to-back ratio (F/B) of Yagi antennas. Traditional LPDAs span broad frequencies with moderate gain and low VSWR, while Yagis provide high gain and F/B over narrow bands. By analyzing high-Tau LPDA designs, it was found they could nearly match the gain of VHF/UHF Yagis while maintaining excellent patterns, F/B, and front-to-rear ratios (F/R). Optimizing specific elements for target frequencies (e.g., 144.1 MHz) led to the Loggi, which uniquely features all driven elements without passive directors or reflectors. This design effectively functions as a narrowband optimized LPDA, with front elements acting like Yagi directors and rear elements like Yagi reflectors, thus enhancing gain and directional characteristics while retaining broad frequency versatility.

TFilter is a free online tool for designing linear phase, optimal, equiripple finite impulse response (FIR) digital filters. It utilizes the Parks-McClellan algorithm implemented in JavaScript. Users can specify the sampling frequency, desired number of taps, passbands, and stopbands to generate a filter. An example configuration is provided for easy testing.

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

Filter Free is the shareware version of Filter Solutions and Filter Light. Filter Free is limited to 3rd order or lower low and high pass filters, 2nd order or lower band pass and band stop filters, and 10 tap or lower FIR filters, and does not include most of the advanced design capabilities of Filter Solutions and Filter Light.

Effective suppression of harmonics and parasitic radiation from HF transmitters is crucial, especially with the increasing sensitivity of VHF/UHF radio channels to interference. This project details a hybrid low-pass filter (LPF) designed to operate across the HF bands up to 51 MHz, making it suitable for 6-meter band operations while providing deep VHF/UHF suppression. The design addresses the challenge of modern interference landscapes, where even microvolt-level signals can disrupt wireless sensors and other simple VHF/UHF receivers. The filter utilizes a single elliptic link, combining high cutoff steepness with robust suppression in the hundreds of megahertz range. A key feature is the use of only two standard capacitor values, simplifying construction and component sourcing. The article provides a detailed schematic, performance characteristics, and _RFSim99_ model file, demonstrating a reflection coefficient S11 below 0.017 (VSWR < 1.03) across 1-51 MHz, ensuring minimal degradation to the antenna system. Construction notes include coil winding specifications and capacitor selection guidance, with recommendations for _FR-4_ assembly. Two capacitor sets are presented, with the first variant recommended for its lower RF current demands, keeping currents below 3 A at 1 kW passing power at 51 MHz. Fine-tuning involves adjusting frameless coils, with considerations for capacitor tolerance and high-frequency capacitance measurement accuracy.

This project details the development of a modular direct conversion (DC) receiver designed for experimental flexibility in amateur radio and HF signal listening. The mainframe integrates a diplexer, DBM, and AF amplifier, supporting interchangeable local oscillator and antenna filtering setups. A tunable passive HF preselector complements QRP Labs bandpass filters for enhanced signal reception. Utilizing a NanoVNA for precise tuning, the receiver achieves improved signal-to-noise ratios across amateur and non-amateur bands, making it a versatile platform for further RF experimentation.

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.

Connecting to the global *EchoLink* network via a web browser simplifies internet linking for licensed amateur radio operators. This web application provides a direct interface, eliminating the need for client software installation. Users can log in with their validated callsign and password to access the system, facilitating contacts with other stations, repeaters, and conferences worldwide, much like traditional VoIP applications but tailored for amateur radio. The interface offers essential controls for managing connections, including selecting specific stations or conferences from a dropdown list, initiating a connection, and disconnecting. Features such as a 'Call CQ' button allow users to signal their availability for a contact, while options for low bandwidth operation and accepting incoming connections optimize performance and accessibility. Audio device selection ensures proper microphone and speaker integration with the web client. Validation of an amateur radio license is a prerequisite for full access, ensuring that only authorized operators utilize the network. The system prompts unvalidated users to provide an email address and password to begin the validation process, which typically involves submitting proof of license. This free service extends the reach of amateur radio communications globally, bridging geographical distances through internet connectivity.

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.

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.

Andrew Roos (ZS6AA) details his practical approach to building a Single Operator Two Radio contest station within suburban constraints. The article explains how he leveraged a Force-12 C-31XR triband beam's unique separate feed arrangement to operate on two bands simultaneously. Using band-pass filters and an antenna switch, he achieved sufficient isolation between bands without requiring multiple towers. The setup includes automatic band selection, audio switching, and computer control. Testing during the 2007 CQ WPX CW contest confirmed the system's effectiveness, demonstrating that competitive SO2R operation is achievable with limited space and budget.

This article discusses a high performance, 7MHz, 5 watt SSB rig, the Daylight Radio, an all-analog radio design from the 1980s that includes a full circuit diagram, IMD NR60 calculations, QER crystal filter, bandpass filter, receiver portion, and more. The author explores the design, components, and functionality of this analog radio for hams interested in vintage or homebrew radio projects.

The project details the construction of a GM3OXX OXO transmitter, designed to accommodate **FT-243 crystals** using 3D-printed FX-243 holders from John KC9ON. It presents specific frequency adjustments, noting a 7030 KHz HC-49/s crystal could be tuned from 7029.8 KHz to 7031.7 KHz with an internal 45pF trimmer capacitor. The build incorporates a modified keying circuit to prevent oscillator run-on key-up and includes a TX/RX switch for sidetone via a connected receiver, with the transmitter output routed to a dummy load on receive. Practical construction aspects are thoroughly covered, including the process of cutting a rectangular opening in a diecast enclosure for the FT-243 socket and the selection of a **low-pass filter** (LPF) based on the QRP Labs kit, derived from the W3NQN design. The author achieved approximately 800mW output power from a 14.75V supply, measured with an NM0S QRPoMeter, using a 16.5-ohm emitter resistor in the 2N3866 final stage. The article also touches upon the potential for frequency agility across the 40M band using multiple FX-243 units with various crystals. The narrative includes a brief diversion into Bob W3BBO's recent homebrew projects, such as his Ugly Weekender MK II transceiver, highlighting the enduring appeal of classic QRP designs. The author reflects on the personal satisfaction derived from building RF-generating equipment, irrespective of DX achievements, and shares experiences of making local contacts with the 800mW OXO transmitter on 40 meters.

Details the construction and performance of a phase-controlled receiving array, specifically a **MicroSWA** variant, optimized for QRP low band fox hunting on 40M and 80M. The resource documents the author's iterative design process, addressing significant regional noise challenges encountered during 0100-0230 UTC fox hunt periods. Initial experiments involved a director wire on a 40M vertical, yielding limited improvement, prompting a shift towards advanced null-steering techniques. The project leverages concepts from Victor Misek’s "The Beverage Antenna Handbook" and Dallas Lankford’s extensive work on phased receiving antennas for urban lots. A key modification involved integrating a new passive phase control box and a push-pull **Norton common base preamp** using 2N5109 transistors, designed for high third-order intercept performance to maintain weak signal integrity amidst strong adjacent signals. The system incorporates Faraday-shielded transformers with RG174 primaries on -75 ferrite cores, housed in ABS plastic pipe. Performance tests confirmed the MicroSWA's ability to produce deep, steerable nulls, achieving approximately 30 dB noise reduction on 160M, 80M, and 40M. This enabled detection of QRP signals undetectable on conventional transmit antennas. The final unit includes front panel controls, a 10-11 dB preamp, and a robust power conditioner, demonstrating effective noise mitigation for challenging low band QRP operations.

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.

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.

TX5EU 2026 DXpedition to Raivavae Island, **OC-114**, within the Austral Islands, providing a detailed account of the German/Dutch team's operations. The resource outlines the participation of operators such as DL2AWG Guenter, PA2KW Evert, and DK2AMM Ernoe, who engaged in CW, SSB, RTTY, and various digital modes. It documents the real-world challenges encountered, including significant equipment failures and antenna damage to 80/60m, 30m, and 10m verticals due to adverse storm conditions. The page offers timely news updates on the expedition's progress, noting repairs to a power amplifier's 10/12m bandpass filter, which enabled three stations to utilize amplification. Earlier reports highlighted power failures and the loss of multiple power amplifiers, necessitating one station to operate barefoot FT-8 with 100W. The team's persistent efforts to repair antennas as weather permits are also detailed, reflecting the dynamic nature of remote island operations.