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A free online calculator for making all of the calculations required to design and build small transmitting loop antennas, also known as magnetic loops by 66pacific.com

If you have ever tried transmitting on HF from a tall block of apartments, where it's just not possible to erect a substantial aerial system, then this article is for you

The "REAL TIME ANTENNA GAIN COMPARATOR SYSTEM" by IK0BDO details a low-budget amateur radio tool designed for optimizing homebrew VHF/UHF antennas. It facilitates the simultaneous comparison of two antennas, one a known reference (e.g., a dipole) and the other under test, displaying their relative gain directly in decibels. The system addresses limitations of previous measurement benches by enabling on-field optimization, accounting for balun performance, impedance mismatching, and cable losses. The core of the device is an electronic solid-state switch utilizing PIN diodes, which alternates signal sampling from the two antennas 100 times per second. This rapid switching prevents the receiver's Automatic Gain Control (AGC) from compensating for signal differences, allowing for precise comparative measurements. The document includes detailed schematic diagrams for both the RF switching unit and the associated measure unit, which employs two VU-meters to display cyclic signal levels. It also provides guidance on setting up the PIN diode switching with an oscilloscope and adjusting trimmer potentiometers P1, P2, and P3 for optimal operation. Further sections cover the construction of VHF (144.150 KHz) and UHF (432.360 MHz) beacons for testing, along with critical considerations for selecting an appropriate test range or site. Recommendations include maintaining a minimum distance of 50 wavelengths between transmitting and receiving positions, avoiding ground reflections, and using reference antennas with gains similar to the antenna under examination. The author notes satisfactory results from measurements on dipoles and other antennas, highlighting the system's ability to appreciate fractional decibel differences.

Progress in Design of Extremely Short Transmitting Antennas Short and still efficient, how is that possible? By Juergen Schaefer, DL7PE author of the MicroVert antenna concept. The MicroVert introduced in this document is an extremely short and hardly visible short-wave antenna with outstanding radiation properties

For radio amateurs seeking compact and efficient antenna solutions, particularly for restricted spaces or noise reduction, HF loop antennas present a viable option. This resource compiles several articles from the ARRL, detailing the theory, design considerations, and practical construction of various loop configurations. Topics include small transmitting loops, receiving loops, and multi-band designs, often emphasizing their performance characteristics such as directivity, bandwidth, and impedance matching. The collected articles provide insights into the comparative performance of different loop geometries, such as circular versus square loops, and discuss the impact of conductor size and tuning methods on efficiency. Practical applications are explored, including their use in portable operations, stealth installations, and urban environments where noise mitigation is critical. The content often includes construction diagrams, parts lists, and performance data derived from modeling or field tests, enabling hams to replicate or adapt the designs for their specific operating conditions.

The NCDXF/IARU International Beacon Project operates a worldwide network of 18 high-frequency radio beacons, continuously transmitting on 14.100, 18.110, 21.150, 24.930, and 28.200 MHz. These beacons, initially launched in 1979 with a single station and expanded to the current 18-beacon system in 1995, provide reliable signals for both amateur and commercial users to assess current **ionospheric propagation** conditions. The system's design, construction, and operation are managed by volunteers, covering hardware and shipping costs. The resource details the evolution of the beacon network, including the transition from Kenwood TS-50s transmitters to Icom IC-7200 radios with a new controller design implemented in 2015. It explains how listening for these 100-watt signals, transmitted to vertical antennas, allows operators to determine band openings and optimal propagation paths globally. The content also references three QST articles providing historical context and technical specifics of the beacon project. Practical information includes methods for identifying transmitting beacons via a schedule or specialized software like FAROS and Skimmer, which integrates with the **Reverse Beacon Network** for automated monitoring.

A switchable Magnetic Transformer for Transmitting for various impedances

Article about small magnetic loop antennas with notes on realization of magnetic loops for several HF bands and the six meter band

A system designed to automatically tune small transmitting magnetic loop antennas, particularly beneficial for **contest operations** where rapid frequency changes are common. The core of the system involves a PC-based control application, AutoCap, written in C#, which monitors antenna SWR via an external meter and commands a motor interface to adjust the loop's variable capacitor. The software is compatible with Windows and Linux via the Mono framework, offering a graphical user interface for monitoring system status, SWR, power, and motor commands. Key components include one or more magnetic loop antennas equipped with DC or stepper motors for capacitor adjustment, an SWR meter with data output (such as the Telepost LP-100A or a homebrew serial/USB SWR meter), the AutoCap PC software, and a motor interface. The most effective motor interface utilizes an **Arduino-based controller** with custom firmware, providing precise control over both simple DC motors and stepper motors, and supporting features like motor braking for finer adjustments. The system allows for configurable SWR thresholds, pulse widths, and motor effort settings to optimize tuning speed and resolution. Optional radio integration provides frequency hints, enabling the algorithm to learn the relationship between motor actions and resonant frequency, thereby speeding up initial tuning responses. The software also supports antenna profiles, allowing operators to save and recall specific configurations for different loops, including accumulated frequency hint data.

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

Getting the most out of LowFER transmitting antennas, designing an efficient antenna for the 1750-meter band by K0LR

Article from 73 Amateur Radio Today about experimenting on ferrite loops transmitting loop antennas for 80 and 160 meters bands.

Antenna directivity and gain are fundamental concepts for any radio operator, as this article from _Electronics Notes_ explains. Real-world antenna designs, unlike theoretical isotropic radiators, do not radiate equally in all directions; their radiation patterns are often visualized using **polar diagrams**. These diagrams illustrate how power is focused in desired directions, crucial for both transmitting and receiving applications. The article clarifies how antenna performance is identical for both transmission and reception, a key principle for understanding antenna specifications. Operators often encounter terms like _beamwidth_, which defines the angle where power falls to half its maximum level, or -3dB. Understanding this parameter is vital for accurately orienting directional antennas like a Yagi. The discussion also differentiates between antenna gain expressed in dBd (decibels over a dipole) and dBi (decibels over an isotropic source), noting that dBi figures will always be **2.1 dB** higher than dBd. This distinction is critical when comparing antenna specifications to ensure an accurate assessment of performance. Furthermore, the article touches on the front-to-back ratio, another important metric for directional antennas, and the balance between maximizing forward gain and achieving an optimal front-to-back ratio.

How to improve your transmitting antennas for very low solar activity periods, vertically polarized 160 meter antennas, horizontally polarized 80 to 10 meter antennas, single or stacked yagis, multi-tower stations

Amateur Television (ATV) operations involve transmitting and receiving live or recorded video and audio signals over amateur radio frequencies. Unlike narrow-band modes, ATV utilizes a wider bandwidth to convey video information, often requiring specialized transceivers, antennas, and signal processing equipment. This mode allows hams to share visual content, demonstrate projects, or conduct video conferences, typically on VHF, UHF, and microwave bands due to the bandwidth requirements. The SwissATV resource focuses on the technical aspects and community engagement surrounding ATV within Switzerland. It covers topics relevant to setting up ATV stations, understanding signal propagation at higher frequencies, and participating in local ATV activities. The site serves as a central point for Swiss ATV operators to exchange knowledge and coordinate transmissions, fostering the growth of this specialized amateur radio mode.

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.

The video delves into the fascinating science behind antennas, which are crucial for receiving and transmitting electromagnetic waves. It explains how antennas convert electric signals into electromagnetic waves for transmission, and how they operate through the oscillation of positive and negative charges in dipole arrangements. Practical antenna implementations, such as dipole antennas for TV reception and Yagi-Uda antennas with reflectors and directors, are also discussed alongside modern dish TV antennas with parabolic reflectors for signal processing. It's a comprehensive overview of how antennas work and their significance in communication technology.

Operating in a Single Operator Two Radios (SO2R) setup, especially with beverage antennas, often exposes the receiving radio's front-end to significant RF energy from the transmitting radio. This resource details a practical, homebrew receiver protection circuit designed to mitigate this risk. The core of the design involves a non-inductive 2W 22 Ohm carbon composition resistor in series with the RX antenna line, followed by two stacks of four fast-switching diodes (e.g., _1N914_) configured in opposite polarizations. This arrangement effectively clamps the incoming voltage to approximately 2.8 V peak-to-peak, safeguarding sensitive receiver input components. The series resistor plays a crucial role by absorbing excess power, preventing the diodes from exceeding their current ratings and potentially failing open, which would leave the receiver unprotected. The author, _N4KG_, measured up to 50 watts of coupled power between 80M slopers on the same tower, highlighting the necessity of such protection. The design is presented as a cost-effective solution to prevent damage to receiver input transformers, with the author noting successful protection of a receiver even after a resistor showed signs of overheating. This simple circuit can be integrated via a transverter plug, offering a robust defense against high RF input.

A magnetic loop antenna designed for 14 MHz. This kind of antennas is also known as STL, small transmitting loop and can be an excellent solution when you are not allowed to put antennas on your roof

Learn about the practical design and construction of Yagi antennas for ham radio operators. This post explores the benefits of Yagi antennas in receiving and transmitting RF signals, concentrating signal energy in one direction for long-distance communication. Discover the theory behind Yagi antennae, the importance of element size and spacing, and the resources available for sizing and construction. Whether you're interested in OTA television or amateur radio communication, understanding Yagi antenna design can enhance your signal reception and transmission capabilities.

This innovative antenna tuning unit (ATU) enables QRP operators to match their antennas without transmitting RF signals. Using a noise bridge technique instead of traditional transmit-and-tune methods, it achieves truly silent operation. The design incorporates an L-match network with switched inductors and variable capacitor, handling impedance matching from 3-30MHz. Operating from a 9V battery, it includes a built-in RF power meter and dummy load for QRP transmitter testing. The compact unit is particularly suitable for portable operations where minimal RF emissions during tuning are desired.

The most basic form of repeater receives communication on one frequency and re-transmits it on a different frequency, a process known as duplex communication. This capability significantly extends the range of handheld and mobile radios, as repeaters are typically situated at elevated locations with high-gain antennas and greater transmit power. Repeaters commonly operate with FM modulation on the VHF (30 MHz – 300 MHz) and UHF (300 MHz – 3 GHz) amateur bands, which are ideal for portable and mobile devices. Access to repeaters is often controlled by a CTCSS or PL tone, an inaudible signal that prevents the repeater from retransmitting background noise. This mechanism ensures efficient use of the frequency and prevents illegal continuous transmission. Canadian regulations, for instance, require an Advanced amateur radio license and an available frequency within the band to set up a repeater, each assigned a unique call sign and transmit frequency. Configuring a radio for repeater use involves knowing the repeater's transmit frequency, its receive frequency offset (e.g., -600 KHz for VHF or +5 MHz for UHF), and the necessary CTCSS tone. The article references resources like Repeater Book for locating repeaters and provides practical examples for initiating and concluding a basic repeater session, emphasizing clear identification and concise communication.

Compare the efficiency of two HF (or VHF) antennas by simultaneously transmitting FT8 on nearly the same frequency and analyzing PSKReporter SNR data. Determine the effectiveness of your new antenna compared to the old one in dB, to several decimal places. Run FT8 on two transmitters with different call signs and equal power, connected to each antenna. AntennaCompare analyzes global signal reports, isolating antenna performance.