Search results

Optimizing the impedance transformation and common-mode current suppression in antenna systems often involves selecting an appropriate balun. This project presents a **hybrid balun** design, combining characteristics of both voltage and current baluns to achieve superior performance, particularly when used with an antenna tuner. The design addresses issues like **common-mode current** on the feedline, which can distort the antenna's radiation pattern and introduce RFI in the shack. The construction details include winding techniques for the toroid core, component selection, and practical considerations for integration into an existing antenna system. Performance comparisons are drawn against conventional balun types, highlighting the hybrid balun's effectiveness across the HF bands. The resource provides insights into the current distribution and impedance matching properties, crucial for efficient power transfer and reduced SWR.

Constructing a compact, directional antenna for the 6-meter band presents unique challenges, especially for operators with limited space or those seeking portable solutions. This project details the build of a 50 MHz Moxon rectangle, specifically engineered for balcony or temporary mast deployment, using readily available materials from a typical hardware store. The design emphasizes ease of construction and portability, allowing for quick setup and breakdown. The antenna's dimensions are precisely calculated using _Moxgen_ software for 50.200 MHz, ensuring optimal performance. Key construction techniques include using aluminum U-channel for elements, fiberglass driveway markers for insulation, and cable ties for secure assembly. The guide provides detailed instructions for fabricating the driven element, reflector, and boom, including a clever method for creating foldable element tips for transport. Performance observations indicate a respectable front-to-back ratio, capable of reducing an S7 signal to S0 when pointed away, and a modest gain over a simple wire antenna. The design incorporates a ferrite bead choke balun at the feedpoint to mitigate common-mode current and reduce shack noise, a critical consideration for urban or apartment-based operations.

The 10-meter EH Antenna document details the construction and performance of a specific EH antenna design for the 10-meter band. It describes the integration of an L+L balanced matching network, a key component for impedance transformation, and highlights the addition of a tuned coaxial trap. This trap, consisting of 8 turns of RG58 coax wound around PVC tube and resonated at 29 MHz with a 10 pF capacitor, effectively inhibits common-mode current on the feeder, stabilizing antenna tuning. The resource presents a circuit diagram in Figure 1 and assembly details in Figure 2, illustrating the use of PVC plumbing tube as host material for dipole cylinders made from recycled aluminum tubing. It also explains the fabrication of capacitor stators and slider sections from thin aluminum tubing. The author, Lloyd Butler VK5BR, discusses initial challenges with feeder interaction and how the tuned trap resolved these issues, leading to stable tuning. Limited backyard tests indicate that the antenna, with the trap fitted close to the input connector, might exhibit similar field strength for both low and high angle transmission, suggesting a potential skewing of the signal. The document references previous articles by VK5BR in "Amateur Radio" for further operational details of the matching network and trap functionality.

The QRP choke balun described utilizes a high permeability ferrite rod and RG-174 coax, aiming to present high impedance to common-mode currents across the HF spectrum. The construction involves winding as many turns of RG-174 as possible around the ferrite rod, then encapsulating the assembly with hot glue. This design prioritizes maximizing inductance to suppress unwanted shield currents, particularly in unbalanced antenna configurations. While the balun's effectiveness is subjectively reported as good, a potential design consideration involves the dielectric properties of the hot glue. This material could increase turn-to-turn capacitance, potentially reducing the balun's performance at higher HF frequencies, though this specific aspect has not been formally tested by the author, _AA5TB_. The project serves as an illustrative example of a practical, junk-box construction rather than a rigorously engineered solution. Photographs detail the evolution of the balun, from the initial winding process to its integration within a _B&W dipole center insulator_ and final camouflaged assembly.

Amidon Associates, Inc. provides a comprehensive selection of inductive components, including ferrite toroids like the FT-50-61 and FT-50-43, alongside iron powder toroids such as the T50-2. These cores are frequently employed by radio amateurs for constructing baluns, ununs, and RF chokes, essential for impedance matching and common-mode current suppression in the shack. The company also supplies ferrite beads, split cores, and cable clamp-ons, which are critical for mitigating EMI and RFI in various electronic systems. Beyond core materials, Amidon offers mounts, bobbins, tunable inductors, and specialized wiring components like PTFE tubing, catering to diverse project requirements. They also provide custom winding services, allowing for tailored solutions in both amateur and commercial designs. Top-selling items include the BN-61-202, a common choice for broadband transformers, and the FB-43-801 ferrite bead, often used for decoupling and parasitic suppression in RF circuits. Amidon further expands its inventory by distributing products from other manufacturers, including Gowanda Electronics and Leader Tech, Inc., broadening the range of components available for hams and engineers.

Protecting amateur radio equipment from transient overvoltages requires robust lightning and surge protection, which is the focus of Electronic Specialty Products. The company provides various devices, including coaxial lightning arrestors for antenna feedlines and surge protectors for AC power lines and data circuits. These devices are engineered to divert high-energy surges, such as those caused by direct or indirect lightning strikes, away from sensitive transceivers, amplifiers, and computer components, thereby preventing catastrophic damage. Key products include the _Coaxial Lightning Protector_ series, designed for various impedance levels and frequency ranges up to 3 GHz, and the _AC Line Surge Protector_ for shack power distribution. Effective deployment of these protection devices can significantly reduce the risk of equipment failure and ensure operational continuity during severe weather. For instance, a properly installed coaxial arrestor can handle peak currents of **20 kA**, while AC line protectors offer clamping voltages typically below 400V. Comparing different models reveals varying levels of insertion loss and return loss, with some coaxial units exhibiting less than 0.1 dB loss at 500 MHz, making them suitable for high-performance HF and VHF/UHF operations. Integrating these components into a comprehensive grounding system is crucial for achieving maximum protection against both common-mode and differential-mode surges.

Stop common-mode current when transmitting with an end-fed antenna. Unbalanced antennas are very prone to currents on the outside of the coax.

Presents a construction project for a 1:1 current balun, specifically detailing the _Sorbie Balun and Bottle Choke_ design. The resource outlines the winding technique, employing 4+4 turns of mini coaxial cable on a large ferrite core, and provides insights into the physical assembly. It includes specific material recommendations, such as the type of ferrite and coaxial cable, crucial for achieving the desired impedance transformation and common-mode current suppression. The content covers the practical steps involved in building the balun, from preparing the coaxial cable to securing the windings on the ferrite toroid. It also discusses the integration of the balun into an antenna system, emphasizing its role in maintaining pattern integrity and reducing RF interference in the shack. The resource offers a clear, step-by-step approach, making the project accessible for homebrewers. Illustrations and photographs accompany the text, visually guiding the builder through each stage of construction. The article concludes with performance expectations and considerations for deployment, ensuring the constructed balun functions effectively across the intended frequency range.

Operating a ham station often involves encountering radio frequency interference (RFI), RF feedback, or RF burns, which are frequently misattributed to poor equipment grounding. This resource meticulously dissects these assumptions, asserting that RF grounds on the operating desk often merely mask more significant system flaws. It identifies five primary causes for RF problems, including antenna system design flaws, proximity of the antenna to the operating position, DC power supply ground loops, equipment design defects, and poorly installed connectors or defective cables. The content emphasizes that issues like "hot cabinets" or changes in SWR when connecting a ground indicate substantial RF flowing over wiring or cabinets, a phenomenon known as common-mode current. The article provides detailed explanations of common-mode current generation, particularly from single-wire fed antennas like longwires, random wires, and OCF dipoles, which inherently present high levels of RF in the shack. It also illustrates how vertical antennas, lacking a perfect ground system, can excite feed lines with significant common-mode current. Through simulations, the author demonstrates how a dipole without a proper _balun_ can cause RF problems at the operating desk, showing current patterns and voltage distributions on feed line shields. The discussion extends to the proper application of _RF isolators_ and _ferrite beads_, clarifying their role in modifying common-mode impedance on cable shields and cautioning against their use as a band-aid for fundamental system defects. The resource advocates for correcting the actual source of RF problems, such as antenna system issues or poor connector mounting, rather than relying on internal shack grounding or isolators. It highlights that properly functioning two-conductor feed lines, like coaxial or open-wire lines, should result in minimal RF levels at the operating position, even without a desk RF ground. The author shares personal experience, noting that his stations since the late 1970s have operated without RF grounds at the desks, relying instead on proper antenna system design and feed line integrity.

This EXCEL Program Worksheet calculates the common-mode impedance of a 1:1 Guanella (current) balun which is placed at the feed point of a balanced antenna system fed via coax.

The resource, "Conventional Use of Transmission Line," meticulously details the operational principles of transmission lines, emphasizing the Transverse Electromagnetic (TEM) mode of energy transfer. It clarifies that for a line to function purely as a transmission line, all currents must be confined internally, with external fields ideally zero. The discussion differentiates between balanced and unbalanced lines, asserting that while both require equal and opposite currents within the conductors, the key distinction lies in the voltage relationship of each conductor to the surrounding environment. It highlights that a good antenna pattern does not inherently confirm proper feeder balance, and that common-mode currents can lead to RF in the shack and increased noise levels, even without pattern distortion. The article further explains that a transmission line can become a radiating conductor if energy is applied in a non-TEM mode, leading to common-mode issues. It cites classic texts like Jordan and Balmain's "_Electromagnetic Waves and Radiating Systems_" and Kraus's "_Antennas_" to support its definitions of TEM mode operation. The content also explores non-transmission line applications of parallel or concentric conductors, such as _coaxial dipoles_ and _folded dipoles_, which intentionally operate in non-TEM modes for antenna functionality. The author, _W8JI_, stresses that simply measuring equal currents is insufficient to confirm a balanced feeder; phase and voltage balance to ground are equally critical.

This page provides a detailed guide on the Guanella Current Balun for ham radio operators. The author shares very nice schematics, photos, and explanations on the construction and use of this type of balun. The content explains when a balun is needed and how it can help with common-mode currents in antenna systems. It also discusses the construction process, including winding the balun around a ferrite core. This resource is useful for hams looking to improve their antenna systems and reduce common-mode currents for better performance. This article is in Dutch.

Our ideas about HF baluns have changed dramatically in recent years. The focus today is very much on suppressing unwanted common-mode RF currents, to reduce both the received noise levels and the risks of causing interference on transmit.

Constructing a dual-band antenna for 40 and 20 meters often involves compromises in size or complexity. This resource presents a compact _open sleeve dipole_ design that addresses these challenges by using 450-ohm ladder line and folded elements to achieve a total length of approximately **17.17 meters**, significantly shorter than a full-size 40-meter dipole. The design leverages electromagnetic coupling, where a primary radiator handles the 40-meter band, and a second conductor resonates on 20 meters without direct electrical connection. This configuration eliminates the need for traditional traps, loading coils, or switching components, simplifying construction and reducing potential loss points. The antenna is fed with RG-58C/U coaxial cable, and a common-mode choke is recommended at the feed point to suppress sheath currents, ensuring a cleaner radiation pattern and minimizing RF in the shack. The design is well-suited for portable operations, field deployments, temporary installations, and restricted urban environments where space is a premium, offering solid performance on both HF bands.

How many times have you heard the advice to coil a few turns of coax at the antenna end to form a choke. How to find out if your common mode current choke really works

This article clarifies the roles of baluns, ununs, common mode chokes, line isolators, and impedance transformers in amateur radio. A balun decouples balanced antennas from unbalanced feed lines, preventing interference. Ununs serve a similar purpose for asymmetrical antennas. Common mode chokes and line isolators suppress common mode currents, reducing noise. Impedance transformers adjust antenna impedance to match feed lines but do not decouple or suppress common mode currents. Understanding these components is crucial for optimizing antenna performance and minimizing interference.

This comprehensive three-part guide examines baluns (balanced-to-unbalanced devices) and their critical role in ham radio antenna systems. The author explains how baluns prevent common-mode currents on feedlines, which can distort radiation patterns and cause unwanted RF in the shack. Various balun types are analyzed, including coiled coax chokes, ferrite-core designs (W2DU), and toroidal-wound versions (Guanella/Ruthroff). Construction techniques for 1:1, 4:1, 6:1, and 9:1 current baluns are provided with practical guidance on wire selection, winding methods, and ferrite core properties. The article emphasizes that proper balun implementation is essential for optimal antenna performance, especially with directional arrays.

This article addresses the issue of unwanted RF in amateur radio setups and introduces a practical method to measure common-mode currents (CMC) using a homebuilt RF meter. The meter, constructed with readily available materials, measures unwanted RF on the coaxial cable shield by inductively coupling to the shield using a split-bead ferrite. The article provides detailed instructions on building the meter, interpreting measurements, and using ferrite chokes to mitigate RF interference. Emphasis is placed on the importance of verifying CMC levels and installing chokes to improve equipment performance.

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

Detecting stray RF voltages on station grounds, chassis, and interconnecting cables is crucial for preventing program and hardware failures in the shack. This article details the construction and application of an LED RF V-probe, which offers significantly higher sensitivity compared to conventional neon lamp indicators. The probe leverages two specific properties of modern red LEDs: their ability to glow at microampere currents and their rectification capability at frequencies up to tens of megahertz. The design features a simple circuit with two LEDs, allowing for indication of both positive and negative RF voltage half-waves. The minimum detectable RF voltage is approximately 2 V, a substantial improvement over the 40-60 V threshold of neon bulbs. The resource illustrates the probe's physical construction on a PCB and provides a direct comparison demonstrating its superior sensitivity in detecting RF fields near a coil. Two operational modes are described: a non-contact mode for high RF voltages (above 15-20 V) and a direct-contact mode for measuring lower RF voltages, with a safety caution for the latter. Practical examples show the probe's use in analyzing RF voltage distribution across a radio station setup at 1.84 MHz and 24.9 MHz, revealing insights into common-mode current issues and the effectiveness of mitigation strategies like adding radials.

VE2AZX's 2013 Radio Talk presentation details the technical aspects of baluns, including reasons for their use, various types, and methods for performance verification using an SWR analyzer. The document specifically examines 1:1 voltage baluns and 4:1 voltage baluns, outlining their winding configurations and typical impedance transformations. It presents empirical SWR measurements for W2AU 1:1 baluns and Unadilla 4:1 baluns, tested with both 50-ohm and 200-ohm resistive loads across the HF spectrum. The presentation further explores the measurement of ferrite impedance and their application in mitigating common-mode currents on feeders and household conductors. Key concepts addressed include balanced-to-unbalanced transformation, ensuring feeder independence from the antenna, and reducing unwanted feeder radiation. The content emphasizes practical testing procedures to ensure optimal antenna system performance and minimize RF interference. Discussions also cover open-circuit tests with SWR analyzers and VNAs to assess winding inductance, distributed capacitance, and insulation quality. The presentation differentiates between voltage and current baluns, explaining how current baluns, particularly those utilizing ferrite cores, reduce outer shield currents without affecting internal coaxial cable currents, thereby preserving the antenna's intended radiation pattern.

This page details the construction of a portable dual-band 2m/70cm Yagi antenna, designed for full duplex satellite operation with radios like the Anytone AT-D890UV. The author sought a lightweight, self-buildable antenna after reviewing commercial options like the ARRL Dual-Band Yagi. The design is based on DK7ZB's work, utilizing tape measure elements for portability and 3D-printed brackets. The author modified existing Thingiverse designs to adapt for a 19mm boom diameter, reduce size, and simplify the overall structure. The antenna features two elements for the 2m band, with the front element serving as the driven element, and three elements for the 70cm band, including a parasitic element. A five-turn choke is incorporated to prevent common-mode currents. Claimed gain is 4.1 dBd for 2m and 6.2 dBd for 70cm. The article includes design measurements and a photo of the completed antenna, noting that the build cost was minimal as materials were repurposed.