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An interesting article on grounding and receiver noise

A Progressve Communications Receiver by W7ZOI and K5IRK. First published in the November 1981 QST

Amateur radio products,wire and yagi antennas, SDR Receivers, upconverters, pre-amplifiers, towers and RTL funcube dongles by CT1FFU

TYT Electronics boasts of 15-year experience in two-way radio manufacture. Produce DMR transceivers, handhelds, receivers and mobile radios, analog amateur radio and commercial VHF transceivers

SPX Communication Technologies, operating under the TCI International brand, presents a range of radio frequency (RF) solutions primarily for government, defense, and commercial sectors. The offerings include advanced systems for spectrum monitoring, communications intelligence (COMINT), and high-frequency (HF) and medium-frequency (MF) broadcasting and communication antenna systems. Specific product lines encompass _Blackbird_ COMINT systems, _Scout_ spectrum monitoring receivers, and various antenna arrays designed for robust performance in challenging RF environments. The resource details the capabilities of these systems, such as wideband signal detection, direction finding (DF), and signal analysis, crucial for intelligence gathering and regulatory compliance. It also highlights the engineering behind their antenna designs, which are optimized for specific frequency ranges and operational requirements, including high-power broadcast applications and secure military communications. The information presented emphasizes the integration of hardware and software for comprehensive RF situational awareness. The company's focus on empowering partners to "Command the Spectrum" underscores its commitment to delivering critical tools for signal interception, analysis, and management across diverse operational landscapes.

For over 50 years, Communications Specialists Inc. has been a cornerstone in specialized radio frequency solutions, initially gaining prominence with their **CTCSS** and **DTMF** tone signaling products widely used in amateur radio repeaters and commercial two-way radio systems. My own experience with their tone boards in various repeater builds confirms their reliability and ease of integration, a testament to their engineering. The company's legacy in tone encoding and decoding is well-established, providing robust solutions for access control and selective calling. Beyond tone signaling, Com-Spec has diversified into niche markets, including wildlife telemetry, pet tracking collars, and specialized tracking systems for model aircraft and rocketry. Their product line features compact transmitters and receivers designed for specific tracking applications, demonstrating a commitment to precision and durability in challenging environments. While some legacy products are no longer available, Com-Spec continues to innovate, as evidenced by the new R-30M receiver, which ships within five days. This focus on specialized RF applications, from tracking Alzheimer's patients to law enforcement, highlights their unique position in the radio communications industry.

Mobile RFI, often manifesting as persistent noise in the receiver even with the antenna disconnected, frequently originates from the vehicle's power supply system. This guide details systematic troubleshooting steps, beginning with isolating the radio from the car's 12-volt supply to confirm the power system as the noise source. It emphasizes the critical importance of drawing power directly from the battery using **heavy gauge wire**, bypassing the fuse block to leverage the battery's natural capacitance for RFI suppression and ensuring a solid RF ground. Proper routing of power lines through the firewall is also covered, advocating for dedicated grommeted holes to prevent inductive coupling from other wiring harnesses. The article stresses the necessity of fusing both positive and negative leads from the battery, a crucial safety measure to prevent damage to the rig and mitigate high-current risks should the battery's engine block ground become compromised during service. Addressing **alternator whine**, a common high-pitched noise that varies with engine speed, the resource suggests checking battery connections and the alternator-to-battery harness for looseness or corrosion. It also mentions the utility of adding an external RF noise suppression capacitor in parallel with the alternator's internal capacitor for enhanced filtering, and the effectiveness of commercially available in-line power supply filters.

This page describes how to make the inexpensive Ten-Tec model 297 noise blanker work with the Drake R-4C receiver.

How to receive automatically NOAA wather satellite images with a Raspberry Pi and a RTL SDR. This project requires a Raspberry Pi 3 Model B a common NooElec SDR Dongle and a QFH Antenna in the attic. Article explains how to setup and configure software but no instructions on antenna.

Featuring Eddystone, Classic British receivers (a history from 1898 - 1973) and Hubble-Bubble a personal web page

_HamDXMap_ provides propagation analysis and operational aids, integrating real-time data with historical logging capabilities. The platform displays Maximum Usable Frequency (MUF) and foF2 response curves, with a horizontal bar indicating live VFO frequency from _Win-Test_ via Gateway software. It supports _VOACAP_ 24-hour propagation predictions for Short Path (SP) and Long Path (LP) tabs, factoring in monthly smoothed sunspot numbers. The minimum bounce altitude for propagation calculations is **50 km**. The tool features a _ClubLog_-sourced DXCC Most Wanted ranking in voice, telegraphy, and digital categories, displayed in callsign pop-ups and DXpedition lists. Users can import contest logs in ADIF format, visualizing QSOs on the map with adjustable line and point parameters. A playback function allows contest replay at speeds from **1x to 100x**. An _IOTA_ (Islands on the Air) layer displays island group definitions and confirmation percentages, indicating RSGB activation evidence requirements. _HamDXMap_ integrates over 1100 online SDR receivers from three networks, updated daily, with access links and a favorites function. It tracks current and future DXpeditions planned over the next 45 days, sourced from _The Daily DX_, _DX 425 News_, _DX World_, _Les Nouvelles DX_, and _NG3K_. Real-time weather information, including temperature, wind, and pressure, is displayed in DXCC country and RX/TX position pop-ups.

Experimental Software for the Yaesu VR-120 and Yaesu VR-120D Receivers

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.

VE3NEA presents a detailed account of designing and constructing a **helical filter** specifically for 144 MHz satellite reception, addressing severe SDR receiver overloading from nearby Land Mobile Radio Network signals between 141 MHz and 143 MHz. The author's experience with RTL-SDR, RSP1a, and Airspy Mini receivers demonstrated the necessity of a narrowband solution to enable reception in the 145.8-146 MHz range with only 3 MHz separation from strong interference. The resource delves into the theoretical underpinnings of helical resonators, drawing upon Anatol I. Zverev's "Handbook of filter synthesis." It explains the equivalent circuit of a two-resonator passband filter, highlighting the critical role of stray capacitance (C3) in determining the coupling coefficient (K) and emphasizing the importance of **critical coupling** (K=1) for optimal filter performance. Misconceptions regarding tap positions and impedance transformation are clarified, with tap placement shown to control resonator loading and the trade-off between bandwidth and losses. Construction details include sourcing materials like 1/4" copper tubing and PCB, precise assembly techniques, and the use of tuning screws for frequency and coupling adjustments. Measurements performed with a NanoVNA revealed discrepancies from initial Coil64 calculations, necessitating adjustments to helix turns and tap positions to achieve the desired 3.5 dB passband loss and 40-50 dB suppression of interference.

Makers of QRP HF General Coverage Transceivers you can build. The Home of BITX transceivers, uBITX General Coverage Receiver-Transmitter. A general coverage, 10 watts HF SSB/CW transceiver kit with features you NEED for operating ease, convenience and versatility. It works from 3 MHz to 30 MHz, with up to 10 watts on SSB and CW, with a very sensitive receiver.

The WB5RVZ Genesis Radio G40 build log documents the construction of a 5W QRP 40m SDR transceiver kit, detailing each phase of assembly from power supply to RF filtering. It provides specific component lists, parts placement diagrams, and testing procedures for stages like the local oscillator, Tayloe detector, and RX op-amps. The resource highlights discrepancies between documentation versions and offers practical advice for builders, including a "virtual build" approach to preemptively address potential ambiguities in component identification and placement. It also addresses a specific "VK6IC Fix" for early board revisions, involving trace cuts and jumper wires for improved performance. The build log presents measured voltages and expected current consumption for various stages, such as the 4.9-5.0 Vdc on the 5V rail and under 100mA for RX current. It outlines critical adjustments like image rejection tuning, a common procedure for direct conversion receivers. The resource also includes practical tips for handling components like the 2N3866 transistor and its heatsink, emphasizing pre-assembly. It details the winding of two 1.45 uH toroidal inductors on T50-6 cores with 17 turns of #20 AWG wire, crucial for the RF path.

Suburban amateur radio repeater is a wider coverage machine with six receiver sites in the chicago metropolitan area.

CATSync V1.30 integrates OpenWebRX support, expanding its capability to synchronize a local amateur radio transceiver's CAT control with a broader range of public WebSDR receivers. The software facilitates real-time frequency tracking, allowing the operator to adjust their physical rig's VFO and observe the connected WebSDR instantly follow the tuned frequency. This functionality is crucial for remote listening, signal comparison, and verifying propagation conditions across different geographic locations using a familiar hardware interface. The application supports both the classical WebSDR interface and KiwiSDR platforms, providing a consistent control experience across various online SDR deployments. It bridges the gap between local station operation and the vast network of globally distributed software-defined radios, offering a practical tool for DXers and contesters. CATSync is designed for Windows and Linux environments, with Android compatibility noted, making it accessible to a wide user base seeking to leverage WebSDR resources with their existing station setup.

Rack Mounts for ham radio transceivers and receivers

Drake R4B receiver manual

These pages document some of the experiments with KB9YIG\'s Soft Rock 40 receiver

Receiver dynamic range is the ability of a receiver to receive a weak signal without loss of readability while a strong signal is present.

A great page about RTL-SDR and GNU Radio with Realtek RTL2832U [Elonics E4000/Raphael Micro R820T] software defined radio receiver.

The review details the Elecraft KX3 S/N 963, noting its delivery on July 31 and primary use as a base rig, alongside initial portable operations. It highlights the transceiver's performance across various modes and bands, including observations on its receiver sensitivity and transmit audio quality. Specific operational scenarios, such as field deployments and integration with different antenna systems, are discussed, providing practical insights into the rig's capabilities. The author evaluates the KX3's user interface, menu navigation, and overall ergonomic design for both casual and intensive operating sessions. Attention is given to features like the internal ATU, power consumption during transmit and receive, and the clarity of the display under varying light conditions. Comparisons are drawn to other portable QRP transceivers, emphasizing the KX3's distinctive attributes. Key takeaways include assessments of the _KX3_'s suitability for _RaDAR_ operations and general QRP DXing, based on real-world contacts and signal reports. The article offers a balanced perspective on the transceiver's strengths and areas where users might need to adapt their operating style, making it a useful reference for prospective owners.

A cavity filter, often a critical component in _duplexer_ designs, functions as a sharply tuned resonant circuit, allowing only specific frequencies to pass while attenuating others. These filters are essential for maintaining signal integrity in environments where multiple transmitters and receivers operate simultaneously on closely spaced frequencies, such as in repeater stations. The article details how these filters, sometimes referred to as _notch filters_, achieve high Q factors, which are crucial for their performance. Understanding the principles of cavity filters is fundamental for any amateur radio operator involved in repeater operation or designing custom RF front-ends. The discussion covers the basic circuitry and operational characteristics that enable these devices to provide significant isolation, often achieving **-80 dB** or more between transmit and receive paths. This level of isolation is vital for preventing receiver desensitization and intermodulation distortion. Properly tuned cavity filters ensure that a repeater can transmit and receive simultaneously on different frequencies without self-interference, a common challenge in VHF/UHF operations.

Basics of crystal radios receivers and basic working priciples

A simple Drake R-4C receiver power supply modification

Linrad and SDR-IQ Software Defined Receiver on Shortwave

The purpose of this webpage is to document an attempt at this project starting with the 80m core receiver first and also having the parts on hand for then adding the first dual conversion band (40m)

W1WD review and reception performance test of the Elecraft K3 transceiver.

The basics of radio receiver dynamic range performance used for specifying the performance of radio receivers used in radio communications systems.

The OnAir SDR receiver application, hosted on GitHub, supports a broad range of digital and analog modes across macOS, Windows, and Linux platforms. It decodes various digital TV standards like DVB-T/T2, DVB-C, DVB-S/S2, ATSC, ISDB-T, and DTMB, alongside broadcast audio formats such as DAB+, FM, and DRM. For aviation enthusiasts, it processes ADS-B, ACARS, and VDL2 signals, while also offering satellite reception and GNSS capabilities. Amateur radio operators benefit from its support for modes including FT8, PSK31, and CW, in addition to general digital voice decoding and cell tower monitoring. A built-in spectrum analyzer provides visual analysis of received signals. The project demonstrates active development, evidenced by over **1,750 commits** to its codebase. OnAir is designed for compatibility with popular SDR hardware, including _HackRF_, RTL-SDR, Airspy, SDRplay, BladeRF, LimeSDR, Pluto, and USRP devices. This wide hardware support makes it a versatile tool for radio enthusiasts and professionals working with various SDR platforms.

Reducing noise on six meter band

This article will explain a few of the ways author use an external SDR and Linrad to enhance his K3 experience. Linrad is one of many available SDR receiver programs. The same could be done with any radio that lets you access its IF frequency output. Article from NCJ Nov Dec 2019

Drake R-4C Receiver Manual (Early Version - 6HS6)

Amateur radio repeaters extend communication range for mobile and remote stations by retransmitting signals on a different frequency, often for emergency communications. The resource details various repeater bands, noting that 2 meters and 70 cm are primary for activity, with 10-meter repeaters offering potential national and overseas coverage. It specifies **18 channels** on 6 meters and **31 channels** on 2 meters, along with a new 70 cm offset of _7 MHz_ adopted in 2015. The content explains how repeaters can be linked via dedicated transmitters/receivers, landlines, or Internet VoIP systems like _IRLP_ and Echolink, enabling global connections. It also describes simplex gateways for multi-band operation and the use of CTCSS subaudible tones for access control and interference mitigation. The document highlights specialized repeaters for modes beyond voice, such as SSTV and ATV, particularly on 70cm and higher bands. Operational guidelines for efficient and courteous repeater use are referenced, along with links to Australian repeater listings and band plans.

Javiation page dedicated to the ICOM IC-R20 150KHz - 3305 MHz communication receiver

The Triangle ATV Association is an organization of hams in the Raleigh-Durham-Chapel Hill NC area who communicate by means of our own personal TV transmitters and receivers.

KiwiSDR Software-defined receiver at Bjargtangar Iceland covering HF Bands

Boasting an FM demodulation rate of **1,235 Msps** and a DMR speed of **369x realtime**, SDR-- is a software-defined radio application designed for patching together radio components across macOS, Windows, and Linux platforms. It facilitates connecting a receiver to various channels, which then feed into speakers, maps, or recorders. The software supports a wide array of audio modes including AM, NFM, SSB, CW, FM stereo, RDS, DMR, FreeDV, D-STAR, Fusion, NXDNP, P25, and dPMR, alongside decoding numerous events and messages such as ADS-B, ACARS, VDL2, HFDLA, AIS, NAVTEX, DSC, POCSAG, FLEX, ERMES, FT8, FT4, WSPR, APRS, RTTY, PSK, ISM sensors, and time signals. Beyond audio and data, SDR-- also handles video modes like SSTV, ATVDVB-S, and DVB-S2. It provides comprehensive displays including spectrum, waterfall, constellation, and map views, all integrated with decoded messages. Advanced features include scanning, signal identification, satellite tracking, direction finding, and passive radar capabilities. The application offers remote control options via REST, WebSocket, MCP, and event forwarding, allowing integration with external tools. It can operate on a desktop computer or be deployed on a server, such as a _Raspberry Pi_, for remote access, providing flexibility for shack setups or antenna-side installations.

The Doppler Effect allows the distance between a satellite transmitting from space and a radio receiver on the ground to be measured by observing how the frequency received from the satellite transmitter changes as the satellite approaches, passes overhead, and moves away.

The SDRcom platform provides a unique browser-native Software Defined Radio experience, emulating a traditional radio with a physical VFO dial, switches, and an analog meter. It integrates a high-resolution 64k FFT waterfall display, supporting essential modes like AM, FM, SSB, and CW. The **SDRcom Blue** version interfaces with SDRplay® receivers via a local WebSocket, while the free **Red Lite** version supports RTL-SDR V3/V4 dongles through WebUSB, including basic audio EQ and 100 memory slots, along with FT8 decoding. For advanced operators, the Red Pro version expands capabilities with 1000 memory slots, upgraded high-resolution waterfalls, and enhanced W4PAH FT8, FT4, and WSPR decoder engines. It also incorporates 4-band DSP noise reduction and an intelligent band scanner, proving beneficial for weak-signal work. The Network edition extends functionality to access hundreds of global remote SDRs, and an ADS-B aircraft decoding feature with 3D positioning and mapping is also available. All SDRcom applications are designed to run directly in a web browser, eliminating the need for any software installation. This approach simplifies access and setup for radio enthusiasts, from casual SWLs to dedicated digital mode operators, allowing immediate engagement with the airwaves.

A schematic diagram of a homemade direct conversion receiver for 30 meters band

A fully documented restoration project of a Hallicrafters SX99 receiver

High Performance Communications Receiver AKA, The Progressive Receiver

Maintaining vintage Eddystone receivers often presents unique challenges, as detailed by Victor Jenkins in his refurbishment of an EA12, where his deep understanding of RF circuits ensures optimal performance for daily shortwave listening. Similarly, Gerry O’Hara VE7GUH, a prolific contributor to the EUG website and a trustee, meticulously documented his restoration of an Eddystone S830/2, even addressing an unusual instability issue with a follow-up postscript article and YouTube videos demonstrating the fix. His work, along with numerous other articles on the "Restorations" page, showcases a master's approach to bringing vintage sets back to factory specifications or better. Beyond technical restorations, the EUG also shares compelling historical narratives. One such story recounts the discovery of a long-lost 78rpm recording featuring Eddystone Radio Ltd.'s founder, George Stratton Laughton, and other key figures discussing the company's wartime and post-war contributions to shortwave communications. This six-minute BBC production, transcribed into an MP3 file by Peter Carney, offers a rare auditory glimpse into the company's legacy, highlighting its role in supplying equipment to police, ministries, and expatriate British workers. The community aspect thrives through shared experiences, like Roger Trickett's anecdote about his Eddystone EC10, which has been continuously powered for 50 of its 54 years, traveling across continents and enduring various modifications. Another intriguing account from Roy GM4VKI details the "S640 Identity Crisis," where a seemingly standard S640 receiver turned out to be a masterfully engineered 80/20-meter SSB transceiver built into the original chassis by GI3ZX, showcasing incredible ingenuity from a bygone era of amateur radio.

A tutorial on how to setup a receiver capable to decode SSTV signals with a small RaspberryPi version 2 and a RTL-SDR dongle. The author explains how to install the needed software to interface the RTL-SDR and a step by step guide to install the QSSTV software used to decode the signals.

Two receivers compared, Drake R8A and Palstar R30

Single antenna with multiple polarization for diversity, diveristy receivers and propagation effects on signal polarization

One-Cubic-Inch Direct-Conversion Receiver