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The Icom IC-7300 is a popular SDR transceiver known for its excellent performance in ham bands. However, users have reported issues with reception reliability outside these bands due to ADC aliasing. This phenomenon occurs when the sampling rate of the radio interacts with frequencies outside the intended range, leading to unwanted signals being received. For instance, when tuned between 30 to 36 MHz, users may inadvertently pick up WFM broadcast signals or PMR communications due to aliasing effects. This guide outlines modifications to improve the IC-7300's performance by addressing the low-pass filter design, which is crucial for reducing interference from these unwanted signals. The proposed modifications involve adjusting the low-pass filter on the PA unit to better attenuate frequencies that cause aliasing. Measurements indicate that the original filter design allows significant signal leakage, leading to false receptions. By implementing the suggested changes, users can achieve a notable reduction in unwanted signals, enhancing the overall functionality of the IC-7300. While the modification requires careful soldering, the benefits in performance make it a worthwhile endeavor for serious operators looking to optimize their SDR experience.

Testing a Bencher YA-1 low-pass TVI filter with a spectrum analyzer with tracking generator.

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

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

This document details the construction, programming, and operation of a modular WSPR transmitter. The transmitter utilizes an ESP8266 NodeMCU, an SI5351 synthesizer with a TCXO for stability, and selectable low pass filters. Construction involves soldering headers, components, and assembling filter module. The ESP8266 is programmed via the Arduino IDE, requiring library installations and code modifications, including network credentials, callsign, and frequency . The transmitter is powered by USB or Vin terminals and its frequency is selected by jumpers and software settings. The document also covers FCC restrictions and how to use the WSPR network

Zenith Tracker offers real-time satellite tracking, pass predictions, and radio hardware integration for ham radio operators. The platform includes an interactive world map showing satellite positions, footprints, and ground tracks, as well as a polar radar visualization for detailed pass analysis. Users can view upcoming passes, set filters, and receive notifications. Integration with CSN Technologies S.A.T Hardware and QTRigDoppler allows for automatic radio control, antenna tracking, and transponder management. The platform also offers APRS message interface, grid square-based location input, and API integration for rover activations. Zenith Tracker is recommended for both general users and those needing advanced hardware integration.

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

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.

This is a power amplifier project for a RF 600W 1.8 MHz to 70 MHz linear amplifier including a Low Pass Filter. Projects includes schematics, pictures, PCD design, fans details, note on PA ferrite chokes and assembling instructions

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

An **Arduino LC Meter** provides an accessible solution for precisely measuring inductance and capacitance values, crucial for RF circuit design, filter tuning, and troubleshooting in amateur radio applications. This project details the construction of a low-cost, accurate instrument using readily available components, making it an attractive alternative to commercial units for hams and electronics enthusiasts. The build process involves assembling a resonant circuit, integrating an Arduino microcontroller for frequency measurement, and displaying results on an LCD. Key components include an Arduino Uno, a 16x2 LCD, a 74HC14 Schmitt trigger inverter, and a few passive components. The design leverages the Arduino's processing power to calculate L and C values from resonant frequency shifts. Calibration procedures are outlined to ensure measurement accuracy, which is vital for critical RF work. The project includes schematics, a parts list, and the necessary Arduino code, enabling hams to construct a functional LC meter for their workbench.

A homebrew spectrum analyzer, the Specan, provides a crucial measurement capability often missing from the typical amateur radio shack, allowing for detailed analysis of RF signals up to 70 MHz. This double-conversion superheterodyne receiver design incorporates 112 MHz and 12 MHz intermediate frequencies, utilizing an _Si570_ as the local oscillator for fine tuning down to 1 Hz steps. It offers two resolution bandwidths: 300 KHz for broad spectrum sweeps and 1 KHz for precise close-in distortion measurements, achieving an 80 dB spur-free dynamic range at 1 KHz resolution. The project, a reboot of the classic _W7ZOI/K7TAU_ design from November 1998 QST, integrates an _Arduino_ microcontroller for controlling the Si570, managing a front-panel LCD, and communicating with a PC for spectrum plotting. This approach significantly reduces cost compared to commercial units, making advanced RF diagnostics accessible to homebrewers. The Specan can measure carrier suppression, VFO cleanliness, antenna VSWR, transmitter harmonics, and filter passband shapes, providing insights beyond what an oscilloscope or frequency counter can offer. Construction emphasizes modularity and careful shielding, with each stage built and tested individually on unetched copper clad board. The design includes detailed instructions for integrating the Arduino, building the Si570 oscillator, and aligning the various modules, often using the Specan itself for calibration. It requires a well-regulated linear power supply and can be built with common tools and readily available components, making it a practical and rewarding endeavor for those looking to enhance their RF test bench.

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

The DX Jungle SatTracker is an interactive online tool designed for real-time amateur radio satellite tracking. It incorporates live Doppler correction, AMSAT satellite status, and pass predictions for various active amateur radio satellites such as ISS, SO-50, FO-29, and RS-44. The platform calculates real-time uplink and downlink frequencies, adjusting for Doppler shift, and displays satellite footprints and orbital paths on a map interface. Users can select specific satellites and input their grid square for localized pass predictions. This service integrates WebSDR support, allowing users to listen to satellite passes live without requiring a physical radio, and offers Companion radio control capabilities. Orbital data is sourced from CelesTrak, while radio frequencies are derived from AMSAT and SatNOGS. The interface provides options to filter for FM repeater-only satellites and displays active passes, ordered by the next available pass, facilitating timely operational planning for satellite enthusiasts.

A dual insert microphone design for the Icom IC-7300 transceiver utilizes a **Besson BZ2400 M4 Rocking Armature** insert for frequencies from 500 Hz to 3 kHz, exhibiting a rising response of approximately 11 dB. A generic Electret Condenser insert, powered by the transceiver's microphone line, covers the low-frequency range from 100 Hz to 500 Hz. A Low Pass Filter is incorporated after the Electret insert to prevent frequency overlap, and a pre-set potentiometer (VR1) adjusts the low-frequency response, balancing the output of both inserts. The design emphasizes a "Close Talking" arrangement and addresses audio "colorization" by housing the Besson insert in a thick rubber holder with a foam boot, separate from the circuitry, with the Electret insert also wrapped in a foam boot. Critical importance is placed on using the correct BZ2400 M4 insert with 12 holes in its face plate. The frequency response table for the BZ2400 M4 insert shows 0 dB at 500 Hz, rising to +11 dB at 3000 Hz, while the Electret insert with the Low Pass Filter provides 0 dB at 100 Hz, rolling off to -9 dB at 500 Hz and -50 dB at 3000 Hz. This combination ensures a broad, balanced audio spectrum for SSB operation. The project includes a circuit diagram, a comprehensive parts list detailing components like a 1 Henry iron-cored inductor (L1) and various capacitors, and a board layout within the metal tube. The completed unit provides a tailored audio profile for the IC-7300, enhancing transmit audio quality.

Adding 2 RCA inputs, 1 high impedance filtered audio output RCA 3, 3 HIGH PASS filters, 3 LOW PAS filters to the JRC NVA88 Speaker

This article describes an HF upconverter for the FunCube Dongle Pro. Designed for radio amateurs, the converter extends reception capabilities to lower frequencies (0 Hz to 30 MHz) by mixing them with a higher oscillator frequency (100 MHz). This translates the desired signal into a range detectable by the FunCube Dongle (64 to 1,700 MHz). Key components include a double-balanced mixer and a low-pass filter to suppress unwanted signals. The project provides schematics, filter specifications, and design considerations for construction.

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.

Demonstrates WSPR propagation activity, presenting observed data by reporter, band, UTC time, local time, and user-selected global destination areas. The application allows users to analyze WSPR spots from a live data server or import saved WSPRnet query files, bypassing the 10,000-row download limit by collecting individual band files for busy bands. Users can configure band preferences and destination modes, choosing between city radius or Maidenhead map grids for filtering path destinations. The interface provides options to start current-day live collection, a 7-day continuous archive, or load previously saved data to build the propagation matrix. Diagnostic information and archive history are accessible, alongside map setup controls for grid contrast and visibility. The tool supports both Path 1 and Path 2 map destinations, enabling detailed analysis of WSPR signal paths.

Demonstrates a practical solution for remote reception, the Transceiver-KiwiSDR Bridge, a free Windows utility by GW3JVB. This software links a local amateur radio transceiver to a remote **KiwiSDR** receiver, allowing the KiwiSDR to automatically track the transceiver's VFO frequency and mode. This capability proves invaluable for mitigating local noise, enhancing reception, or simply leveraging the superior receive capabilities of a remote station located globally. The bridge supports a diverse range of transceivers through COM port/CAT connections or **TCI** over a network. Specific compatibility extends to popular models like the Icom IC-7300, systems utilizing the TCI Protocol (such as Thetis, Expert Electronics, Apache Labs ANAN, and Hermes Lite 2), and many radios supported by Hamlib. Experimental Yaesu CAT options are also included, broadening its utility for various shack configurations. Key features encompass automatic mode changes, updates to RX filter bandwidth, and even IC-7300 PBT/filter adjustments. The application integrates a browser extension for Chrome, Brave, and Microsoft Edge, and offers an optional KiwiSDR audio mute during local transmission, ensuring a seamless operating experience. The compact view keeps the interface unobtrusive, with full settings readily accessible.

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.

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.

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.

SWLTools, an iOS application for iPhone and iPad running iOS 17+, provides real-time decoding of various digital modes. It automatically locks onto CW tones, measures sending speed, and collects callsigns, distinguishing valid entries from misreads for a reliable log. For RTTY and SITOR-B, the app allows users to set shift and speed, then automatically tunes to the two tones for text reception, supporting marine bulletins, press agencies, and NAVTEX. The application also decodes WEFAX, building charts line by line for direct saving to the photo library, and processes ACARS aircraft messages, including CRC checks for data integrity and mapping of position reports. Beyond decoding, SWLTools integrates a GPU-accelerated FFT spectrum analyzer, a scrolling waterfall display with frequency cursors, and an adjustable FIR bandpass filter to isolate signals. It supports IQ signal analysis from receivers via two-channel audio interfaces, correcting mirror images. Flexible audio input options include the built-in microphone, USB audio dongles, and Bluetooth sources, with diagnostics for audio routing and buffer status. The app records audio, plays it back, and converts recordings into shareable videos, while decoded texts and charts are also savable and shareable, with all timestamps in UTC.

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.

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.