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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.

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

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

Homemade RF limiter project, to protect the K3 receiver front-end for high radiofrequency based on the original KD9SV project.

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.

When assembling a robust shack, the quality of interconnects often determines overall system integrity and signal fidelity. Neutrik, with over 50 years in the connectivity sector, specializes in professional-grade connectors that withstand rigorous use in entertainment and industrial applications. Their product range includes XLR, speakON, powerCON, and opticalCON series, which are frequently adapted by hams for critical station infrastructure, particularly in contesting or DXpedition environments where reliability is paramount. Amateur radio operators often repurpose these durable connectors for antenna switching matrices, audio interfaces for digital modes, or power distribution systems. The robust locking mechanisms and high-quality contact materials found in Neutrik products ensure stable connections, minimizing intermittent faults that can plague field operations or even fixed station setups. This attention to mechanical and electrical integrity aligns well with the demands of high-power RF environments and sensitive receive chains. While primarily serving the pro-audio and video markets, the engineering principles behind Neutrik's designs translate directly to the needs of radio amateurs seeking superior performance and longevity from their cabling and connection points. Their commitment to innovation, as highlighted by their 50-year journey, suggests a continuous evolution of products that could benefit future amateur radio applications.

In this article the author shows the receiving loop antenna for 160 meters band installed at his QTH. Diagram and movie available. Article in in Turkish but can be translated in english

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.

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

K3AS.com Home Page, Discover SSTV, See K3AS SSTV CAM, Live SSTV Images Received by my Station, View My Station Equipment.

Two receivers compared, Drake R8A and Palstar R30

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 fully documented restoration project of a Hallicrafters SX99 receiver

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

Using Spectrum Lab for the reception of VLF natural radio

KiwiSDR Software-defined receiver at Bjargtangar Iceland covering HF Bands

High Performance Communications Receiver AKA, The Progressive Receiver

Designing and constructing a two-element receiving loop antenna array for HF operation involves specific considerations for achieving high directivity and noise reduction. This resource details a homebrew system comprising two 30-inch diamond-shaped loops, spaced 20 feet apart, which are fed through mast-mounted preamplifiers and passive signal combiners. The operational principle relies on adjusting phase delays between elements via precise _Belden 8241_ coaxial cable lengths, optimized for specific bands from 160m to 20m. Performance data, derived from _EZ-NEC_ modeling, illustrates consistent 90° azimuth-plane beamwidth and low take-off angles across the target bands, with _Receiving Directivity Factor_ (RDF) values comparable to a 300-foot Beverage antenna. The article presents detailed elevation and azimuth plots for 20m, 30m, 40m, 80m, and 160m, demonstrating the array's ability to provide strong response at low DX angles while also supporting _NVIS_ signals. Key components like the _DX Engineering RPA-1_ preamplifier and _DXE RSC-2_ signal combiner are discussed, alongside the importance of impedance matching to preserve antenna patterns. The construction emphasizes self-contained elements that do not require ground radials, offering a compact solution suitable for suburban environments and stealth installations, with a focus on optimizing receive performance independently from transmit antennas.

An improved version of the audio interface commonly used to connect a computer soundcard to a transceiver\'s receive and transmit audio circuits

One-Cubic-Inch Direct-Conversion Receiver

RadioMasterList, a comprehensive receiver and transceiver directory. Performances and specifications for every radio set

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.

Nearly half of all reception problems are due to deficiencies or faults in the television receiver, the aerial lead or the aerial. This article will help you to check whether the problem you are having is due to one of these causes.

This project is a USB Audio, Serial and PTT interface for rigs that does not directly support digital modes provided by applications such as FLDIGI, WSJT-X and JS8CALL. Plug these interface devices into your Windows or Linux laptop or Raspbian Raspberry Pi and you can send and receive digital tones to/from your rig and automate the frequency and mode control and PTT control.

HamAlert let you receive Push,SMS,Email notifications for Cluster,RBN,SOTAwatch spots, with customizable filtering based on many criteria including DXCC, SOTA and WWFF references, CQ zones

Tuned circuits for Progressive Receivers

The equipment shown on this page comprises a basic G3WDG transmit and receive system with the addition of a 1W Qualcomm amplifier.

Build a SPDT coaxial relay that can be used as a main Transmit/Receive relay or an A-B switch to select between two different 6m antennas

tk150 experimental Software for the Standard VR-150 Receiver

This article describes the construction of a high performance transmitter and receiver for SSB (voice) communication covering the 14MHz (20 meters) high frequency amateur radio band with output range 15 to 20 watts and a top audio sound quality both on transmit and receive.

A homemade interface for any android device, allow to receive and trasmitt SSTV PSK RTTY from an android tablet based on the DD7LP original project include demo of a sample DIY kit.

Producers of custom name tags, luggage tags, club badges, Employee Name Tags, Special Event Badges, but also Comtech Amateur Radio Television Transmitters and Receivers D480 filters, Video cameras and accessories.

A very simple experimental short wave radio receiver. This is basically just a crystal radio with two stages of transistor amplification afterwards made with scrap components.

Barest of bones APRS RF position reporter using a Raspberry Pi B+, USB GPS receiver, Baofeng UV-5R, and a mono 3.5mm audio cable between the Pi and the radio

Presents the full owner's manual for the _Drake R-4C_ communications receiver, specifically a late version edition. This resource outlines the comprehensive operational instructions, covering everything from initial setup and tuning to advanced features and controls. Hams can reference detailed diagrams and explanations for proper signal reception across various amateur bands. The manual includes critical information for alignment procedures, ensuring the receiver performs to its optimal specifications. It details the steps required for calibrating the internal circuitry, which is essential for maintaining sensitivity and selectivity over time. My experience with vintage Drake gear confirms the value of these original documents for accurate adjustments. Furthermore, the document provides insights into troubleshooting common issues and performing routine maintenance. It serves as an authoritative guide for anyone operating or servicing this classic piece of amateur radio equipment, helping to preserve its functionality for years of DXing and ragchewing.

Microprocessor based interface designed receives a signal from a Morse key, processes it, and re-transmits it to the radio. A microprocessor in the circuit is pre-programmed with a proprietary algorithm which makes a number of measurements and adjustments to the less percise human generated code.

Sixty-meter repeaters typically use a 1 MHz frequency separation between input and output, while 2-meter repeaters commonly employ a **600 kHz** split and 70-centimeter repeaters use a **5 MHz** offset. This article details the fundamental technical principles of amateur voice repeaters, explaining how they extend VHF/UHF communication range by receiving on one frequency and simultaneously retransmitting on another. It covers essential components such as receivers, transmitters, filters, and antennas, often situated on elevated locations for optimal coverage. The resource delves into the critical challenge of _desensing_—where the repeater's strong transmit signal overpowers its own receiver—and the engineering solutions employed, including antenna separation and the use of high-Q cavity filters. It also explores various control and timing systems, from basic squelch activation to more sophisticated microcontroller-based boards that manage functions like voice identification, time-out timers, and fault protection. Different access methods are discussed, including open access, toneburst, CTCSS subtone, and DTMF, each offering distinct advantages for managing repeater usage and mitigating interference. Furthermore, the article examines repeater linking, both conventional RF methods and modern internet-based solutions, highlighting how linking expands coverage and promotes activity across multiple repeaters or bands. It introduces less common repeater types such as 'parrot' repeaters, which use a single frequency and digital voice recording, and linear translators, capable of relaying multiple signals and modes simultaneously across different bands, often found in amateur satellites.

Receivers and transmitters by Collins , Drake , Hallicrafters , Hammarlund , National Receivers

An SDR project, MDSR modulator-demodulator software radio, made using an inexpensive converter and a pc. MDSR has a transceiver and a receiver converters.

Nexus is a free and open-source ham radio software application, built in Rust by KD9TAW, designed to integrate multiple station functions into a single program. It supports fifteen operating modes, including FT8, FT4, CW, SSB, FM, RTTY, SSTV, and APRS, with both transmit and receive capabilities across Windows, Linux, and Raspberry Pi platforms. The software provides band activity displays with country, distance, and bearing information, a call roster, a 3-D propagation globe with live spots, and alerts for new DXCC, WAS, WAZ, VUCC, and IOTA entities. It also features a native RF panadapter for Icom CI-V and Flex radios, or a live audio scope for other transceivers. Nexus integrates a comprehensive logbook, computes awards offline without requiring an account, and includes repeater search functionality with curated memory packs. It offers CHIRP CSV round-trip compatibility for approximately 1,000 radio models and is compatible with WSJT-X, JTDX, and MSHV via UDP protocol for seamless integration with existing workflows. The application supports ADIF import/export for log data management and provides accessibility features for operators with hearing or visual impairments, including screen reader compatibility and keyboard-navigable interfaces.

Developing operational amateur radio equipment for the 134 GHz band presents significant technical challenges, particularly in frequency generation and stability. This resource details the construction of a 134 GHz system, outlining its architecture with separate transmit (Tx) and receive (Rx) modules, each employing a local oscillator (LO) and RF head units. The system utilizes a dual Flann 50 GHz lens-type horn antenna configuration for optimal signal coupling. The transmit path incorporates an LMX2541 synthesizer chip operating at approximately 2.8 GHz, referenced by a 10 MHz double-oven Morion OCXO for exceptional stability. This signal is multiplied through a series of stages (X4, then X2) to generate a 22.4 GHz signal, which subsequently drives a dual series diode multiplier to produce the final X6 signal for 134 GHz operation. The receive side features an anti-parallel diode mixer coupled to a 144 MHz transceiver via a preamplifier, ensuring effective downconversion. Operational mode is CW, achieved by keying a multiplier stage. The project includes images of the Tx and Rx head units and describes a successful 3.5 km test with G8ACE, demonstrating stable signal tones due to PLLs locked to OCXOs at both ends, confirming the system's robust performance.

A microprocessor based interface designed to go between a standard Morse code key and a radio transmitter. The circuit receives a signal from the key, processes it, and re-transmits it to the radio.

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.

Do you want to see how your FT8 signals are being received in the other parts of the globe?

Since 2011, crkits offer radio kits that you cannot find on eBay or AliExpress. Includes HT-1A 20/40m Dual Band CW Transceiver Kit, D4D DSB Transceiver Kit for Digital Mode, R3500D ARDF Receiver, CW Transceiver Kit

N-channel scalable coherent receiver that employs the RTL-SDR technology in order to create inexpensive multi-channel receiving systems.

A 0-30 MHz step attenuator, constructed from switchable Pi attenuation pads, provides a practical tool for evaluating receiver sensitivity and calibrating S-meters. The design utilizes readily available 5% tolerance resistors, with values derived from paralleled components to achieve specific attenuation steps. A schematic (Fig 1) illustrates the circuit, including PCB pad shielding, while a table details required and actual resistor values, along with percentage differences. Measurements of voltage input versus output at various frequencies are used to calculate dB attenuation, presented in a graph (Fig 4). The resource includes formulas for determining output voltage from a known input and a comprehensive 0-40 dB voltage multiplier table, which is crucial for precise signal level management. The project also references external attenuator calculators and equations for further study. Photos (1-3) provide visual guidance for the assembled unit, showing bottom, top, and front views. The project emphasizes the use of **Pi attenuation pads** and **receiver sensitivity** evaluation, offering a hands-on approach to RF signal management.

Picture gallery of SSTV images received by DU1IVT Thelma

Presented is a historical collection of short-wave listening (SWL) QSL cards, primarily from the late 1930s and early 1940s, offering a glimpse into early international broadcasting and the technical pursuits of SWL operators like Les Miles during that era. The resource showcases specific QSLs from stations such as _Broadcasting Corporation of Japan_, _XGOY - The Central Broadcasting Administration_ in Chungking, China, and _Australian broadcasting ship, Kanimbla VK9MI_, each with reception dates and frequencies like 11.90MHz or 9.525MHz. It highlights the self-sufficiency of SWL enthusiasts who constructed and maintained their own radio and test equipment, evoking the sensory experience of vintage valve receivers. The collection provides concrete examples of international broadcast stations active before and during World War II, including _2RO3 - Rome_ and _WRUL - World Wide Broadcasting Foundation_ from Boston. Each QSL entry details the station, location, reception date, and often the frequency, such as 9.63MHz or 11.26MHz, allowing for historical verification of broadcast schedules. The resource also briefly mentions the operational details of the _VK9MI_ offshore radio station, directing readers to further information on its history. This compilation serves as a tangible record of global radio communication during a pivotal historical period.

Sending the Audio from the Receiver to the Recorder, from the Recorder to the EQ, and sending the Audio from the EQ or Recorder to the Transmitter