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Calculate the inductance of a single-layer, air-core coil.

An air cored 1:1 balun for 3.5 to 30.0 MHz

Details the offerings of Ham Buerger Inc., a company founded in 1965 to support the amateur radio community with communications products. The business provides a range of equipment, including Uniden Digital scanners, and maintains a section for equipment blow-out sales that feature professional 2-way radios and cell phones. Additionally, the company stocks hard-to-find NuTone products and provides repair services for most NuTone equipment. The site also references an Amateur Radio Band Plan and links to other ham radio resources, alongside a new product offering for RV and marine toilets, indicating a diversification beyond core amateur radio supplies.

The W1TAG LF Receiving Loop is a specialized antenna project for LF reception, designed to mitigate local noise and enhance weak signal pickup on the lower frequencies. This square loop, measuring 6 feet per side, utilizes 14 turns of #12 THHN wire wound on a PVC frame, offering a robust mechanical structure. The design incorporates a series-tuned circuit with a coupling transformer, allowing for tuning from over 400 kHz down to _45 kHz_ using a switched capacitor bank. Construction details include the use of 1.5-inch PVC pipe for the frame, with specific measurements for spreaders and drilled holes for wire threading. The two 7-turn sections of wire are connected at the center, providing an option for a center tap. The loop rotates on a 1-inch steel pipe, enabling directional nulling of noise sources. The tuning unit, housed in a box clamped to the PVC, employs a 1:2 step-up transformer wound on an _FT-82-77 core_ and uses relays to switch capacitance values from 50 pF to 6400 pF, providing precise frequency adjustment. The current setup connects to the shack via 100 feet of RG-58, feeding into a W1VD-designed preamp, with plans for a balanced, shielded twisted pair cable upgrade.

SDR# (read SDR Sharp) is a high performance Software Defined Radio application. SDR sharp is a fully featured SDR capable of handling samplerates from kHz level soundcards up to multi hundred MHz dedicated samplers, thanks to its multi-core architecture.

The Deutscher Amateur-Radio-Club (DARC) e.V. serves as the largest association for radio amateurs in Germany and Europe, structured into 24 districts and approximately 960 local chapters nationwide. Its core mission involves fostering amateur radio and establishing favorable conditions for the Amateur Radio Service. The DARC actively participates in international affairs as a member of the **International Amateur Radio Union (IARU)**, ensuring German interests are represented on a global scale. Recent activities include the announcement of the FUNK.TAG in Kassel for April 25, 2026, and the HAMCamp at **HAM RADIO** in Friedrichshafen from June 26-28, 2026, offering discounted participation for young operators up to 27 years old. The club also supports special events, such as a short-term award and special callsign DB15ØWG to commemorate the 150th anniversary of the Weimar–Gera railway line, active from April 1 to June 30. Regular updates, like the Deutschland-Rundspruch 11/2026, cover topics from the status of 70 MHz band permissions to satellite deployments like Ten-Koh 2, and contest results such as the WWA YL event. Propagation forecasts, including Kp indices and solar flux values, are provided by Hartmut Büttig, DL1VDL, offering insights into HF conditions and Gray-Line DX opportunities. The DARC also reports on district elections and space-related events like the Bochumer Weltraumtag, highlighting the diverse engagement of its members.

Demonstrates practical solutions for reducing **Radio Frequency Interference (RFI)** in amateur radio operating environments, specifically addressing issues with PC monitors, receivers, and transceivers. The resource compiles advice from experienced operators regarding the selection and application of ferrite cores, including split cores and toroidal cores. It details specific material types like **43, 73, 75, and 77 ferrite**, outlining their effective frequency ranges for RFI suppression, such as 43 material for 30-400 MHz and 77 material for 2-30 MHz. The content provides part numbers for various ferrite products from manufacturers like Fair-Rite Products Corp, distributed by Amidon, and discusses their impedance characteristics across different HF bands. It compares the performance of various ferrite materials at frequencies like 4 MHz, noting that 75 material offers 27 ohms, 73 material 17 ohms, and 43 material just under 10 ohms. Additionally, it touches upon the use of bypass capacitors in conjunction with ferrites to create low-pass filters, emphasizing the importance of identifying common-mode versus differential-mode RFI paths for effective mitigation.

Online calculators for toroid coil, air-core coil inductance, XL, XC, and more.

Article showing how I've made a mains filter to reduce EMC in the electricity supplying my shack. I've used a type 31 Fair-Rite ferrite core and the video shows how this performs on 160m through to 40m.

The main function of the Ugly Balun is to help eliminate rf currents from flowing on the outside of coaxial cable using the principle of choke action.

Operating as a local amateur radio club, the Wireless Association of South Hills (WASH) provides a community hub for hams in the Pittsburgh, PA area, identified by the N3SH callsign. The club engages in a range of activities including the Annual Field Day, the PA QSO Party, and a 2 Meter Contest, fostering participation in various aspects of the hobby. WASH also supports local ARES/RACES efforts, highlighting the critical role of amateur radio in emergency communications during disasters, and facilitates ARRL/VEC exam sessions for new licensees. Beyond contests and emergency preparedness, WASH hosts club picnics and an annual hamfest, promoting social interaction among members. The club maintains VHF/UHF repeaters, which are essential for local communication and extending range for members. Regular activities include a Monday evening WASH NET at 8:00 PM, providing a consistent on-air gathering point. The club's focus on both recreational and public service aspects of amateur radio, from making new friends to providing vital disaster communications, underscores its comprehensive approach to the hobby.

A 102-inch vertical whip, commonly a CB antenna, forms the core of this low-profile 10-meter antenna design, optimized for the 28 MHz band. The construction details specify three 8-foot radials made from scrap wire, connected to a common point. This simple yet effective setup is designed for ease of construction and deployment, making it accessible for operators with limited space or materials. The design emphasizes using readily available components, including PVC pipe for the mast and a SO-239 connector for the feedline, ensuring a straightforward build process for a resonant quarter-wave vertical. Field results indicate that this antenna provides good performance for local and DX contacts on 10 meters, despite its compact footprint. The author, N8WRL, shares practical insights into its construction and tuning, highlighting its suitability for temporary or permanent installations where a full-sized antenna might be impractical. Comparisons to more complex designs suggest that this low-profile vertical offers a respectable signal-to-noise ratio and effective radiated power for its size, proving that simple designs can yield satisfying on-air results.

Two different ways to create autotransformer for end fed half wave wire antennas, by using ferrite or air core.

The program can be used to calculate inductors (coils) and their number of turns on ferrite cores, ferrite shells and air coils. These can be used for baluns, Ununs, bandpass filters, low pass filters, resonant circuits, and more. The technical specifications of the cores are already integrated in the program. Application is free and runs on Windows 32 bit versions only. To make it run on Windows 10 64 bit need to be unzipped in a single folder.

Online calculator for Input coil data, LC Resonant Frequency and L match

The Malaysian Amateur Radio Transmitters' Society (MARTS) serves as the national representative body for amateur radio operators across Malaysia, having been established in 1952. This organization plays a crucial role in advocating for the interests of Malaysian hams, fostering community engagement, and supporting the growth of the amateur radio service within the country. MARTS actively participates in national and international amateur radio affairs, often collaborating with organizations like the _International Amateur Radio Union_ (IARU) to ensure the continued development and recognition of amateur radio. The society's activities encompass a range of services for its members, including the dissemination of information regarding licensing, operating procedures, and technical advancements. MARTS also facilitates various on-air events and provides resources to help members improve their operating skills and expand their knowledge base. The organization's long-standing presence since 1952 underscores its commitment to the amateur radio community in Malaysia. MARTS supports local clubs and individual operators, promoting best practices in radio communication and emergency preparedness.

Provides custom battery pack assembly services, focusing on portable power solutions for two-way radio applications. The company distributes batteries from numerous manufacturers, ensuring a broad selection for various radio models. This includes replacement packs for popular brands such as _Kenwood_, _Icom_, and Yaesu handheld transceivers, as well as batteries for CB radios and scanners. The core business function involves designing and building specific battery configurations to meet unique customer requirements, extending the operational life of portable radio equipment. Their offerings support a wide range of amateur radio activities requiring reliable, field-deployable power sources. Advanced Battery Systems also supplies individual cells and components, enabling radio operators to repair or rebuild existing battery packs, potentially saving costs compared to purchasing new OEM units. They emphasize durability and performance in their custom builds, aiming for **extended cycle life** and **consistent power output**.

Demonstrates MegaPhase's extensive product line of RF and microwave coaxial cable assemblies and components, engineered for demanding applications up to 110 GHz. Key offerings include _Test & Measurement Cables_ with superior phase and amplitude stability, _RF & Microwave Cables_ utilizing _GrooveTube®_ technology for high power systems, and a range of RF components like directional couplers and power dividers. The site details specific cable types such as _Alumibend™_ for space-qualified, ultra-light applications through 90 GHz, and armored cables designed for rigorous environments up to 50 GHz, emphasizing their robust mechanical strength and measurement repeatability. The resource highlights applications across diverse sectors, including space programs like the _Hayabusa_ mission, global security (C5ISR), military airborne systems (MIL-T-81490), telecom, and automated testing. It also provides technical insights through "How To" guides on measuring amplitude/phase stability vs. flexure and proper connector cleaning. The company's commitment to quality is underscored by its rigorous testing protocols and a strong warranty, ensuring reliable operation in critical systems.

Demonstrates the practical application of APRS (Automatic Packet Reporting System) through the lens of HB9PVI's activities in Switzerland. It covers the system's core function of reporting geographical positions and telemetry data from various objects, including mobile stations, aircraft, and the ISS, distributed via packet radio and internet gateways. The resource highlights the routing paradigm shift introduced in April 2005, specifically the recommendation to use _WIDE1-1_ instead of RELAY and WIDE for digipeating to reduce duplicate packets. The page presents real-time maps displaying the positions of amateur radio stations in Switzerland and around Bern, updated every few minutes. It details specific callsigns like _HB9BA-2_ (HB9PVI's home QTH), _HB9BA-8_ (a weather station), and _HB9BA-4_ (a WIDE digipeater on Weissenstein mountain), providing context for their roles within the local APRS network. Links to track HB9PVI's mobile operations (_HB9PVI-9_) and handheld devices (_HB9PVI-15_, _HB9PVI-7_) are also provided. Furthermore, the resource curates a list of APRS software options for various operating systems, including _JavAPRS_ for Europe, _UI-view_, and _X-Astir_ for Linux, alongside digipeater/IGATE software like _DiXPRS_. It also offers downloadable APRS information, including a PDF article by HB9PVI and HE9ZGN, and a PowerPoint presentation in German, making it a repository of practical and historical APRS data.

Demonstrates the activities and mission of ARMIC, the Association of Visually Impaired and Disabled Radio Amateurs of Catalonia, operating under the callsign EA3RKR. The organization focuses on making amateur radio accessible to all, particularly those with visual impairments, by providing resources and fostering a supportive community. It highlights their commitment to inclusive radio operation within the amateur radio service. ARMIC's initiatives include an accessible radio school, emphasizing practical construction projects and operational techniques tailored for members. The association actively promotes participation in various amateur radio activities, ensuring that visually impaired operators can engage fully with the hobby. Their work underscores the importance of adaptive technologies and methods to overcome physical barriers in radio communication. This resource reflects ARMIC's dedication to building an accessible radio environment, aligning with the broader goals of the Grupo Social ONCE, a Spanish organization supporting blind and visually impaired individuals.

A 60-foot available space, for example, might necessitate a shortened multiband dipole array to cover 80, 40, and 15 meters effectively. This resource details the construction of such an antenna, combining full-size and coil-loaded dipoles on a single feedline. It addresses the common challenge of fitting multiple HF bands into restricted physical footprints, providing practical guidance for hams with smaller backyards or portable operations. The core of the offering is an interactive calculator that determines required loading coil inductance and dipole lengths for various amateur bands from 160m to 10m. Users input their available space, and the tool provides dimensions, coil turns, and an efficiency rating (Good or Fair) based on the antenna's electrical length relative to a quarter-wavelength. It also suggests suitable _PVC_ pipe diameters for coil forms. The article further illustrates a center feed-point assembly using an 18-inch section of 2-inch _PVC_ pipe, detailing eye-bolt spacing and coaxial connector installation. It emphasizes the importance of adequate spacing between parallel dipoles and offers customization options for the feed-point, including the addition of a _Balun_ for improved feedline isolation.

This air-core solenoid style RF inductor calculator calculates the inductance, wire size, number of turns, and other parameters for an air-core solenoid inductor used in radio frequency (RF) circuits, based on user input of frequency, desired inductance value, and physical dimensions.

Visualizes real-time amateur radio propagation spots using data from the PSK Reporter MQTT stream, providing immediate situational awareness for radio operators. The platform displays spots from various modes, including CW, WSPR, and JT65, in addition to the dominant FT8 digital protocol. FT8 Live focuses exclusively on live data streams, prioritizing current signal activity over historical archiving, which differentiates it from the official PSK Reporter map. A key feature is its integration with the Summits on the Air (SOTA) API, facilitating SOTA chasing by cross-referencing transmitting callsigns with SOTA alerts; a station is identified as an activator if the spot correlates with a scheduled alert within an eight-hour window. The user interface was developed by Arron (ZL1AN), with core data from Philip Gladstone (N1DQ), and stream delivery managed by Tom Stanton (M0LTE).

Over 1000 _Elecraft_ KX2 owners have benefited from the Kx22 Heatsink, experiencing cooler rig temperatures and higher output powers. PAE manufactures these heatsinks, along with AC power supplies for HF transceivers, remote power relays, and Ethernet relays, with all machined products manufactured in the **USA**. PAE distributes _Fair-Rite_ Mix 31 ferrite snap-it cores and toroid cores, essential for RFI suppression and impedance matching in amateur radio setups. The product line also includes commercial monitoring antennas, UQUI transformers, ULP AC power filters, and 3M conductive adhesive copper tape, catering to various station build-out and maintenance needs. The AM1 Portable Antenna Mount System and its AM1-VA Multi-Angle Adapter offer flexible antenna deployment options. PAE ensures careful packing of fragile ferrite products, with shipping cost adjustments communicated post-order for larger, heavier combinations to guarantee safe delivery.

The article by Guy Olinger, K2AV, published in the May/June 2012 National Contest Journal, introduces the Folded Counterpoise (FCP), a compact 516-foot single-wire counterpoise elevated at 8 feet, designed for 160-meter operations on small lots like 100x150-foot backyards. Originating from efforts to revive Top Band for W0UCE on a postage-stamp property, the FCP uses strategic folds to cancel ground fields within 33 feet of center, minimizing losses to 0.13-0.53 dB—outperforming sparse or on-ground radials by up to 15 dB in poor soil—while mimicking opposed radials for efficient feedpoint impedance. Paired with a critical 1:1 or 4:1 isolation transformer (e.g., trifilar on T300-2 toroid) to block common-mode currents on coax feeds, it delivers proven results: K2AV's #8 North America low-power contest score, 7+ dB gains at W4KAZ and K5AF, and over 10,000 global web hits for DIY instructions using bare 12 AWG wire and weatherproof enclosures. Ideal for acreage-challenged hams, the FCP also excels on 80 meters with scaled dimensions, offering a low-loss alternative where full radials are impractical

Online impedance calculators grouped by types like Wire inductances, Toroid incuctances, Plane, PAD, Strap inductances, but even Core and Coax Inductances. Air core inductances and mutual inductance groups are also availbale. All these calculators let you input specific paramenters based on the inductor selected and will calculate specific incutance and related dimensions.

Integrating a _Software Defined Radio_ (SDR) into an existing ham radio setup involves connecting it with a standard transceiver (TRX), power amplifier (PA), and antennas. The core component is a splitter box that facilitates the connection between the TRX and the SDR, allowing for simultaneous operation without modifying existing equipment. In receive mode, the splitter ties the antenna inputs of both the TRX and a direct conversion receiver (DC RX) together. During transmission, the DC RX input is grounded via a fast telecom relay controlled by the transceiver's -SEND signal, incorporating a 10ms delay for safety. The splitter box includes a 3.7 dB input attenuator for impedance matching and acts as a protective fuse for the DC RX input. Ground loops are mitigated using common mode balun transformers, while the DC RX input is insulated with a broadband transformer. An audio switch box complements the setup, enabling users to listen to either the main transceiver, the SDR output, or both simultaneously. This configuration ensures noise immunity and safety, with the splitter housed in a screened box made from PCB material. On-air tests, such as the CQ WW 160m CW DX Contest, demonstrate the system's effectiveness, showcasing the SDR's ability to handle crowded band conditions with superior selectivity and dynamic range. The SDR's narrow bandwidth filters and waterfall display provide significant advantages, allowing operators to detect weak signals amidst strong interference. The integration of SDR with conventional radios offers enhanced operational flexibility and performance in challenging environments.

Demonstrates practical **rules of thumb** for selecting and utilizing ferrites and coils in amateur radio projects, particularly for RF applications up to 30 MHz. It addresses common challenges like determining appropriate ferrite grades and estimating L/C values without precise specifications. The resource details the author's experience with readily available grey ferrites, noting their suitability for HF work, and provides guidance on constructing **baluns** and RF chokes, balancing inductance for lower frequencies against inter-wire capacitance for higher frequencies. It also outlines a method for estimating power handling based on ferrite weight, suggesting a 1-gram ferrite can manage over 2 Watts, and offers a technique for evaluating unknown ferrites by winding 10 turns and measuring resonance with a 1 nF capacitor. This approach emphasizes a hands-on, iterative method for balun winding and adjustment, allowing operators to quickly approximate component values. The article compares the characteristics of ferrite-cored coils with air-cored coils, highlighting the reduced pickup and radiation of ferrite designs. It refines the air-coil estimation method for frequencies between 2.5 MHz and 10 MHz and provides a scaling factor for frequencies outside this range, aiming to get operators into the correct general area for their designs. The author's standardized ferrite choice (RND Components 165-00182) is presented as a practical example for reproducible projects.

The influence of temperature changes in Common Mode Chokes. To get an indication of the impedance behavior when the core temperature changes, the author tested a CMC by heating it with a hairdryer, and measuring its temperature with an infrared thermometer. When the CMC temperature rises from 30C to 90C, the frequency of maximal impedance shifts down from ca.10 MHz to ca.7.2 MHz, or by a factor 1.4.

The article "Icom IC7300 RTC Fix" details the meticulous repair of an Icom IC-7300's faulty real-time clock (RTC). The author and a friend, Nacho, discovered the RTC was gaining an unacceptable 11 seconds per day. Investigations revealed the Seiko Epson RX8803LC RTC was far outside its specified stability. Despite replacing the RTC and a burned pullup resistor, the transceiver still malfunctioned, leading to the replacement of the processor. Post-repair, the clock's accuracy improved significantly, now gaining only 1.4 seconds per month. This narrative underscores the complexities of electronic repairs and the satisfaction of resolving intricate issues.

Online Coil Inductance Calculator. To calculate the inductance of a single-layer, air-core coil, just select the measurement units, enter the number of turns, the coil diameter and the coil length.

Operating amateur radio satellites presents unique challenges, particularly concerning antenna design and signal propagation. Juan Antonio Fernández Montaña, EA4CYQ, recounts his three-year journey into satellite communication, starting with initial guidance from EB4DKA. His early experiments involved a portable 1/4 wave VHF antenna with four 1/4 wave ground planes, designed for hand-held use to adjust polarity. This setup, paired with an FT-3000M transceiver, allowed full-duplex operation on **VHF** transmit and **UHF** receive, proving effective for early contacts on satellites like AO27, UO14, and SO35. EA4CYQ's experience highlights the critical role of coaxial cable loss and antenna polarization. After encountering significant signal degradation with longer RG213 runs, he experimented with a 1/2 inch commercial cable, noting improved reception but persistent fading due to varying satellite polarities. This led to the construction of an **Eggbeater II** antenna, an omnidirectional UHF design offering horizontal polarization at the horizon and circular right polarization at higher elevation angles. Subsequent modifications resulted in the directional **TPM2** antenna, which provided sufficient gain for LEO satellites with a wide 30-degree lobe, enabling consistent contacts from his home station. The article concludes with practical insights on the performance of the Eggbeater II for both UHF and VHF, and the TPM2 for UHF, emphasizing their utility for portable and fixed operations. EA4CYQ's journey underscores the iterative process of antenna development and the importance of adapting designs to overcome real-world propagation challenges in satellite communications.