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Brugtgrej presents a Danish online classifieds platform specifically for amateur radio operators and electronics enthusiasts. The platform facilitates the buying and selling of used equipment, including transceivers like the Icom IC-7410, various components such as X'TAL FILTER FMT-15A and TRANSISTOR 2SC3019, and accessories like Sadelta microphone capsules and SMA to SMA extenders. Users can post free advertisements for items they wish to sell or acquire, covering categories beyond amateur radio, including antique radios, military radios, and radio tubes. The site lists active advertisements, with 3136 online ads and 167 online users at the time of analysis, indicating a dynamic marketplace. It also features a forum for community interaction, discussing topics like repeater rings on 1297 MHz and FT8 activity. The platform's structure supports both 'Sælges' (for sale) and 'Købes' (wanted) listings across its various sections. Specific items observed include a Miniwatt pentode 4689, various capacitors and coils, and general electronic components, demonstrating the breadth of offerings available to the amateur radio community.

Operating a QRP station in frigid conditions presents unique challenges, particularly concerning power management and equipment reliability. This resource outlines a specific winter portable configuration, focusing on maintaining operational capability when temperatures drop significantly. It details the use of a _Yaesu FT-817ND_ for digital QRP modes, paired with a _Raspberry Pi_ for digital signal processing and logging, demonstrating a practical approach to cold-weather field communications. The article provides insights into selecting appropriate power sources, such as LiFePO4 batteries, and managing their performance in sub-zero environments. It also covers shelter considerations, including tent selection and heating strategies, crucial for operator comfort and equipment protection during extended activations. The author, _OH8STN_, shares firsthand experience from Arctic Circle operations, emphasizing robust gear choices. Further content includes a video walkthrough, illustrating the physical setup of the station, antenna deployment, and the overall operational workflow in a winterized environment. This visual aid complements the written text, offering a comprehensive view of the entire portable station, from the transceiver to the power system and the protective shelter.

technics, radio astronomy, great links, duplex filter

This tutorial provides background information on the decibel and instructions for performing calculations involving decibels. This tutorial combines information from several authors, including Bob DeVarney, W1ICW; Walter Bahnzaf, WB1ANE; and Ward Silver, NOAX

Test and measurements equipment, hp hewlett packard wavetek wandel goltermann wandel

A modification of the UV3R Baofeng handheld transceiver to improve the built in low pass filter

The mod requires an INRAD 45,705 MHz Crystal Roofing filter and the IC-765 add-in Board

Multi-Polarized antennas for Land Mobile Radio, Indoor & Outdoor Networks, Home Wireless, Mining Communications, Remote Monitoring, HAM & Scanner, Cellular, WiFi, Wimax, M2M, GPS, LTE, and GSM.

NEScaf: A Switched Capacitive Audio Filter

The _Touch CPO_ circuit offers a unique method for Morse Code practice, eliminating the need for a physical key. It leverages the versatile IC555 timer, configured as an astable multivibrator, to generate an audio tone. Users can adjust the tone's frequency by manipulating a 100 K variable resistor connected between pins 7 and 6 of the IC555, providing flexibility in the practice experience. Volume control is achieved via a 10 K variable resistor, while a 1 K Ohms preset at pin 4 of the IC555 allows for fine-tuning the touch plate's sensitivity. The design connects the touch plate to the base of a BC147B transistor, a configuration noted for its flexibility regarding the length of wire between the transistor and the touch plate. The author's prototype successfully used a 9 cm wire with a 3 x 6 cm aluminum plate. This project also suggests an alternative application as a touch-operated doorbell, demonstrating the circuit's adaptability. The design emphasizes simplicity and ease of construction, making it accessible for hams interested in DIY electronics.

The IC703 features a built-in DSP filter and auto ATU as well as speech processing an a CW keyer with 3 message memories. It is an ideal all-in-one ham station for QRPers.

How to build a low-pass filter to remove alternator whine from your car

Martek Power designs and manufactures a wide of high performance power supplies for various industries. Power supplies AC-DC, DC-AC inverters, DC-DC, EMI Filters

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

Offer performance comparable to tin-box filters, and except for being bigger, stack up pretty well with those expensive little helical jobs. You just have to be able to make your own PC boards.

PSK Reporter provides a real-time visualization of amateur radio digital mode reception reports, aggregating data from a global network of monitoring stations. This platform is particularly useful for operators utilizing modes such as FT8, FT4, and PSK, allowing them to observe signal propagation paths and assess their station's reach. The interactive maps display reception reports, enabling hams to analyze band conditions and optimize antenna performance for various frequencies and times of day, aiding in understanding ionospheric conditions. Operators can filter reports by callsign, band, mode, and time, gaining insights into specific propagation events or evaluating the effectiveness of their transmit setup. The data collected helps in predicting optimal operating windows for DX contacts across various digital modes. Philip Gladstone is the contact person for comments and discussions regarding the system.

The TVI filters described in this page worked very well in curing a TVI problem on 2m abd 70cm

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.

Operating in the **microwave** spectrum, Response Microwave, Inc. specializes in the design and manufacturing of RF and microwave signal processing components and subsystems. The company's product line encompasses a wide array of offerings, including Connectivity Series components, rotary joints, phase shifters, cable assemblies, surge protectors, terminations, Hybridline/Couperline products, circulators/isolators, directional couplers, quadrature hybrids, attenuators, custom assemblies, filters/diplexers, DC blocks & bias tees, power dividers/combiners, laser diodes & drivers, high-frequency connectors, and precision test accessories. This extensive catalog supports various applications requiring precise signal manipulation and transmission at elevated frequencies. The resource provides access to a comprehensive product catalog and a dedicated connector catalog, detailing specifications for components like **high-frequency connectors** and test cables. While specific performance data or comparative analyses are not directly presented on the main page, the breadth of products indicates a focus on providing foundational building blocks for microwave systems. The company emphasizes customer service and aims to be a reliable source for RF/Microwave/Optics product requirements, serving a growing customer base with its specialized component offerings.

The original SurplusEQ.com domain, once a hub for amateur radio operators and electronics enthusiasts seeking test equipment, meters, and various high-tech components, has been repurposed. Historically, such platforms facilitated the acquisition of essential gear for shack setups, antenna analysis, and general electronics work, often providing cost-effective alternatives to new retail purchases. The site's previous focus on "test equipment, meters, testers" directly supported the technical aspects of the hobby, from RF measurements to circuit diagnostics. Currently, the domain points to a gambling platform named "SEMUTWIN," offering online slot games, live casino options, and other digital wagering activities. This shift represents a complete departure from its former identity as a resource for surplus electronics and amateur radio-related equipment. The content now features game titles like "Sweet Bonanza Super Scatter" and "Gates of Olympus Super Scatter," alongside promotional offers for online gaming.

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.

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.

How to limit unwanted harmonics from your raspberry Pi radio transmitter by introducing filters.

Drake TR-7 A.M. Transmit Filter Modification

F4FAP maintains a useful listing of current saltellites that are on the air and that can be easily heard and worked.

Examples of absorbtive low-pass filters in which the unwanted high-frequency energy is separated from the wanted output and then dissipated in matched resistors

Realization of confortable communications. RF Filters

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.

Modem Telephone Super Filters For HF and AM Radio Interference.

30m lowpass filter for the Softrock Ensemble RXTX tranceiver.

Custom EMI Filters, AC DC Three phase filters by Filter Concepts Inc.

Icom 706MkIIG Filters, Make a narrow CW filter work in SSB for the digital modes

Ultra High Efficiency Alternative Energy System Controllers

The San Bernardino Microwave Society, operating under the callsign _W6IFE_, serves as a significant technical hub for amateur radio operators specializing in frequencies above 1 GHz. This organization's influence extends across Southern California, providing a centralized resource for advanced RF experimentation and **regional frequency management** within the microwave spectrum. Its permanent value lies in its extensive archive of technical papers and project documentation, which are critical for operators engaged in high-frequency design and deployment. The society's infrastructure is primarily intellectual, focusing on the dissemination of specialized knowledge rather than a conventional repeater network. It offers a robust collection of technical papers from prominent members like K6PIP, K6BLG, and WA6EXV, covering topics such as Rubidium oscillator data, logging software, and filter design. This resource facilitates advanced amateur radio operations, including participation in microwave contests and the development of custom transverters for bands like 24 GHz. The site also details various member projects, such as the Owens Valley Radio Observatory Project, showcasing practical applications of **RF propagation analysis** and system integration. DXZone Focus: Microwave | Technical Papers | RF Propagation | Contest Results

A quick and easy logging application designed for BCL and shortwave listeners, requires a recent Windows OS and .Net Framework

Station QRP presents various **circuit diagrams** for constructing low-power AM vacuum tube shortwave transmitters, catering to enthusiasts interested in vintage radio technology. The resource details schematics ranging from simple to more complex designs, enabling hams to build their own QRP AM transmitters for operation on frequencies like 6.925 kHz AM. It emphasizes the use of vacuum tubes, providing a technical foundation for understanding and replicating classic shortwave broadcasting methods. The content is geared towards those who enjoy the hands-on aspect of electronics and the unique characteristics of tube-based RF circuits. Building these transmitters allows operators to experience the nostalgia of early shortwave radio, with the site specifically mentioning a pioneer station on 6.925 kHz AM. The designs facilitate experimentation with low-power AM transmission, offering practical application for homebrew projects. The focus on QRP (low power) operation aligns with a segment of the amateur radio community that values efficiency and minimalist setups, providing a distinct alternative to modern solid-state transceivers.

This article shows how to make a mains filter that can be extremely effective in reducing and in some cases eliminating completely EMC from the electricity supplying your shack

an overview, introduction or tutorial about the basics of electronics filters including the types of filter and the various filter design considerations and parameters

Personal page fron IV3ONZ andrea

Antuino is an accurate instrument that can be used in the field to measure SWR, field strength, modulation, etc. In the lab, it can be used to sweep filters, measure gain, distortion, frequency response, etc. It works upto 150 Mhz. On the third harmonic, it is usable on 435 Mhz band as well (with reduced sensitivity).

How to receive NOAA weather satellite with a home made QFH Antenna. This project includes some easy and efficient notch filters to suppress noise from FM frequencies

On December 12, 1901, Guglielmo Marconi successfully received the first transatlantic wireless communication, a Morse code "S" (three dots), at 04:30 GMT. This article details the setup for this groundbreaking experiment, noting Marconi's receiver in St. John’s, Newfoundland, Canada, utilized a _coherer_ and an antenna elevated by balloons and kites. The transmitting station at Poldhu, Cornwall, England, featured twenty-four 200-foot ships' masts and a 25-kilowatt alternator. The resource explains how this contact disproved contemporary beliefs about radio wave limitations due to Earth's curvature, later understood through _ionospheric propagation_. It frames Marconi's achievement as the "very first DX" in amateur radio terms, defining DX as telegraphic shorthand for distance and _DXing_ as the hobby of receiving distant signals. The article also provides external links for further reading on Marconi's experiments and the science behind transatlantic radio signal reception.

Lightning Arrestors, High current filters manufacturer

One common semiconductor material, silicon, is far more widely used in electronics than germanium, partly because it can operate at much higher temperatures. Semiconductors are crystalline materials with electrical resistivity values between conductors and insulators, whose conductivity can be altered through _doping_ with impurities like arsenic or phosphorous to create N-type (excess electrons) or P-type (electron vacancies) materials. Semiconductor devices, such as diodes, transistors, and integrated circuits, leverage these properties to control electron flow in circuits. A diode, a two-terminal device with an anode and cathode, primarily permits current flow in one direction, making it useful as a rectifier to convert AC to DC. Specialized diodes include Zener diodes for voltage regulation and Light-Emitting Diodes (LEDs) that produce light when current passes through them. Logic circuits, fundamental to digital electronics, have binary inputs and outputs, performing functions like AND, OR, and NOT gates, and can be constructed from various binary devices including solid-state diodes and transistors. A transistor is an active semiconductor device with at least three terminals (base, emitter, collector), capable of amplifying current. Integrated circuits (ICs), often called chips, are electronic circuits built on a semiconductor substrate, typically silicon. ICs are classified by transistor type (bipolar or MOS) and integration scale: Small-Scale Integration (SSI) with fewer than 10 transistors, Medium-Scale Integration (10-100), Large-Scale Integration (LSI) with 100-1,000, and Very-Large-Scale Integration (VLSI) with more than **1,000** transistors. ICs can be analog, digital, or hybrid, offering virtually limitless functions.

Thsi article describes a microcontroller driven semi-automatic antenna tuner capable of handling power levels up to 150 watts. The device is a low pass filter tuner manually tuned by setting the optimized L/C combination by hand and then storing the values into the EEPROM of the mictrocontroller to recall them later (seperately for each band from 80 to 10 meters including WARC bands)

TIM-CO, an authorized distributor, offers a range of electronic components crucial for various applications, including amateur radio station builds. Their inventory focuses on **connectors**, both commercial and military-grade, which are essential for robust and reliable interconnections in radio equipment and antenna systems. This includes a variety of types suitable for RF applications, ensuring signal integrity. Beyond connectors, TIM-CO provides passive and electromechanical components, fundamental building blocks for any radio circuit or control system. These components are vital for constructing filters, impedance matching networks, and power distribution systems within a shack. Their selection supports both new construction and repair of existing gear. Additionally, the company supplies **RF-coax cable assemblies**, pre-fabricated solutions that save time and ensure proper termination for feedlines and inter-component connections. These assemblies are critical for minimizing signal loss and maintaining impedance matching from the transceiver to the antenna.

WiFi Antenna, WiFi Amplifier, RF Splitters, RF FIlters, Adapter, Video Cable and Custom Connectivity Products

Hamradio, Webcams, Radio and TV-Links by DF3SP Walter

rpitx is a general radio frequency transmitter for Raspberry Pi which doesn't require any other hardware unless filter to avoid intererence. It can handle frequencies from 5 KHz up to 1500 MHz.

A multi tool Windows program that has been designed to offer the EMC RF and Radio Engineer a large variety of tools for Attenuation calculation, VSWR analysis, FIR Filter calculations, EMC system configuration, Radar testing , RF Filter calculation and much more without the need of a live internet connection.