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This document details the design and construction of a Vinecom 6N4 dual-band Yagi antenna for the 50MHz (6-meter) and 70MHz (4-meter) amateur radio bands. The antenna features 9 total elements (4 elements for 50MHz, 5 elements for 70MHz) on a 4.236-meter aluminum boom. Computer simulations using MMANA software predict 7.21 dBd gain on both bands with front-to-back ratios of 16.01dB (6m) and 15.37dB (4m). The design uses 12.7mm diameter elements mounted on a 32mm square boom, weighing 5.7kg total. Practical measurements with an MFJ-269 analyzer confirmed good SWR performance across both bands after element length adjustments.

YF1AR multiband vertical antenna, based on orginal concept by VE7BS. Consist of 6 vertical elements and 6 base radials with a single 50 Ohm feed line.

5 elements Yagi antenna with an 8.7 db gain

A re-usable control & computing platform for antenna measurement, PSK31 digital modems, audio filtering, signal source & VFO, memory keyer by AMQRP

This document contains the detailed instructions to build a homemade lindenblad antenna using a twin-lead as dipole elements. This document contains 9 pages and includes a detailed construction sequence and some drawings to build this antenna for UHF and VHF ham radio bands

This article document a 2 element half wave collinear J-Pole antenna by KC9EOT and KB8OJH

The resource presents a mobile antenna mast mount designed for rapid deployment from a vehicle's trailer hitch, addressing specific design criteria for portability and ease of use. It outlines seven key design goals, including fitting inside a vehicle, handling various mast diameters, and enabling one-person setup without tools. The construction utilizes offset T-handled stainless bolts for tool-free mast securing and a "tab" mechanism to prevent collar slippage. Detailed deployment instructions are provided, covering steps from attaching the bottom collar to securing the mount in the hitch, erecting the mast, and tightening both collars. The author, K0EMT, reflects on potential improvements, such as welding the bottom collar for enhanced stability versus transportability. The project also credits AA0ZC for the physical construction.

Mobile antenna placement presents unique challenges for the amateur radio operator, often requiring compromises between RF performance and mechanical considerations. This resource from KV5R.COM offers practical insights into achieving effective installations, drawing on real-world experience with different vehicle types. It details how factors like ground plane availability, proximity to vehicle structures, and antenna type (e.g., **HF mobile**, **VHF/UHF mobile**) influence signal radiation patterns and overall system efficiency. The author discusses common scenarios, from sedans and SUVs to trucks and RVs, highlighting the impact of mounting locations such as the trunk lip, fender, or roof. Specific attention is given to minimizing RF interference and maximizing radiated power, crucial for reliable mobile communications. Understanding the interaction between the antenna and the vehicle's metallic body is key to a successful mobile setup, and this content provides a solid foundation for making informed decisions.

4 elements Yagi antenna for 28 MHz

The GW3YDX Super Moxon antenna design improves upon the standard Moxon Rectangle by incorporating additional directors in a rectangular configuration, yielding enhanced directivity and gain. For the 6m version, modeling with 4NEC2 and EZNEC+ indicated a 3dB gain increase and a 26.5dB front-to-back ratio, with VSWR below 1.5:1 between 50.0 and 50.3MHz when optimized for 50.1MHz. This design achieves a narrower -3dB power point beamwidth of 60° compared to the original Moxon's 80°, contributing to better QRM rejection. The boom length for the enhanced design is just under 2m, approximately double the original Moxon's, with no increase in wingspan. Construction details include tubing lengths for 6m, 4m, and 2m versions, with specific dimensions provided for elements A through M, measured to tubing centers. For instance, the 6m version uses a 2160mm element A and a 2140mm element H. The design maintains a 50-ohm feed impedance, with practical models showing VSWR plots consistent with simulations after minor adjustments to driven element lengths. The article also references Moxgen software for initial Moxon parameter calculation and NEC/EZNEC model generation. The 2m Super Moxon version measures approximately 30" x 25", demonstrating the compact nature of the design across different VHF bands. The article highlights the antenna's performance in real-world DX contacts on 6m, achieving contacts with over 80 stations in the USA from a modest QTH.

A VHF UHF 5+5 elements yagi antenna by CE4WJK

A DIY project of a WiFi 10 elements Yagi antenna

Accurately determining an antenna's feedpoint impedance is crucial for optimal performance, especially when experimenting with new designs or making adjustments. While SWR meters provide basic information, a full complex impedance measurement reveals the resistive and reactive components, which are essential for proper matching. Modern antenna analyzers, like the _Palstar ZM30_ or MFJ259B, simplify this task, but measurements taken through a transmission line require careful interpretation due to impedance transformation. This resource details a calibration method to precisely account for the effects of the feedline. It explains how a transmission line can significantly alter the measured impedance, illustrating this phenomenon with a Smith Chart example where an 80m antenna's [22 + j6] Ohms feedpoint impedance transforms to [82 + j45] Ohms after a 10m line. The guide demonstrates using a transmission line calculator applet, such as the one by W9CF, to reverse this transformation. It outlines the process of calibrating a specific length of RG174 coax, showing how an initial 26ft estimate was refined to **25.85ft** to accurately predict a known 22 Ohm load, significantly improving accuracy over uncalibrated results.

A 4 elements handitenna for 70 cm band. This is my version of the K5OE Handitenna. This one is a four Element instead of three, as I had less of a crunch on space than he did. The 1st three elements (Reflector, Driven Element, and Director 1) are the same dimensions as his were.

Presents the construction of a 6-meter (50 MHz) Moxon wire beam antenna, detailing the use of #14 AWG THNN stranded wire and a treated wood frame. It covers the assembly of a galvanized pipe mast, emphasizing the use of pipe sleeves for joint reinforcement over threaded couplers to prevent breakage during raising and lowering operations. The resource also describes the integration of a 1:1 current balun, rated for 50-54 MHz, and the use of RG-8X coax for the transmission line, recommending low-loss alternatives like Belden 9913-7F. Further, it outlines a manual rotation mechanism using pipe hanger clamps and carriage bolts for true North orientation, incorporating magnetic declination calculations from NOAA. The antenna's performance is discussed, noting good gain and take-off angle, with SWR tuning facilitated by a Palstar AT-500 manual tuner. An EZNEC+ 5.054 model for the antenna is available for download, alongside predicted radiation patterns and SWR curves, compared with actual AIM-4170C measurements.

A 70cm and 2m 6 elements yagi antenna plan based on the IEEE Transactions on Antennas and Propagation

A 5 band two element quad antenna working from 20 to 10 meters using hardware-store parts or modifying an existing commercial triband quad by KC6T

An inverted triangle Delta Loop Antenna for the 40 meter band made with aluminium pipes, each element is 14,2 meters including a home made aluminium mount.

DF9CY implementation of W1HIS suggestion of inserting a common mode choke into a 40m antennas feed-line.

A Loop Fed Array Yagi antenna for 50 MHz featuring 11 dBi gain and 23 f/b ratio. In this excellent page the author even includes a detailed drawing in DWG format, with element lenght and spacing measures, in a separa file a full list of material list needed to build this yagi antenna including source and price, the EZnec file for this antenna plan, and a lot of pictures of this LFA Yagi for 50 Mhz. A ten page PDF file containing all infos, is also available to download.

A four element 2 meter quad antenna project

Optimizing the ZS6BKW antenna for full HF band coverage often requires specific modifications beyond its standard configuration. This resource details several enhancements, beginning with a simple series capacitor to improve 80m SWR, a technique W5DXP found effective for permanent installation due to its minimal impact on higher bands. Further improvements include a 10-inch parallel open stub for 10m resonance, shifting the frequency to 28.4 MHz with an SWR of approximately 1.8:1, a practical solution for Technician class operators. The document then explores a switchable matching section, adding or subtracting one foot of ladder line at the 1:1 choke-balun, which significantly impacts higher frequency bands and eliminates the need for a tuner on 17m. W5DXP's _AIM-4170D_ antenna analyzer measurements confirm these effects. More advanced modifications involve a parallel capacitor for further 80m SWR reduction, requiring remote switching for multi-band operation, and relay-switched parallel capacitors at specific points on the 450-ohm matching section to achieve low SWR on 60m, 30m, and 15m. These detailed steps, including _Smith chart_ analyses for the challenging bands, aim to transform the ZS6BKW into a truly all-HF-band antenna, reflecting W5DXP's practical experience in antenna tuning.

The resource details the construction of a 3-element Yagi antenna specifically designed for the 6-meter band, providing coverage across 50-54 MHz. This antenna design, originally featured in _QST_ August 2007, emphasizes a short boom configuration while maintaining a wideband response. Key specifications include a 50 Ohm SWR of less than 2:1 across the entire band, achieved through specific element lengths and spacing. The design utilizes aluminum tubing for elements and boom, with detailed dimensions provided for the driven element, director, and reflector. Performance characteristics indicate a forward gain of approximately 7.5 dBi and a front-to-back ratio of 18 dB at 50.125 MHz, according to _NEC2_ modeling. The antenna's compact size, with a boom length of 1.83 meters (6 feet), makes it suitable for portable operations or installations with limited space. Construction involves standard amateur radio workshop tools and materials, with a gamma match for impedance transformation to 50 Ohms. The design prioritizes ease of construction and repeatable performance for the 6-meter enthusiast.

Selecting appropriate cabling for amateur radio installations, whether for antenna feedlines, control lines, or station wiring, is critical for optimal performance and safety. This resource provides access to a manufacturer specializing in a broad range of electronic and electrical cables, including options suitable for various ham radio applications. Their product line encompasses standard and custom cable solutions, designed to meet specific operational requirements for both indoor shack setups and outdoor antenna systems. The company emphasizes _proven quality_ and compliance, with products certified by the Canadian Standards Association (CSA), Underwriters Laboratories (UL), and Intertek (ETL). Their quality management system is registered to _ISO 9001:2015_, ensuring consistent product standards. They offer competitive pricing and utilize AI-logistic tools for reliable on-time delivery, serving customers globally with technical support. Access to detailed technical specifications and an online quote tool is available for registered site members, facilitating precise cable selection for projects requiring specific impedance, shielding, or environmental ratings.

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.

The Cushcraft X7 Tribander assembly and installation manual (P/N 951470, 12/97) provides comprehensive instructions for constructing this 20-15-10 meter seven-element beam antenna. It details the sequential assembly of boom sections, individual elements, and the feed system, including the _MNX7 Matching Network_. The document emphasizes critical safety precautions regarding power lines and RF exposure, alongside recommendations for proper antenna system planning and grounding. Key sections cover verification of parts, detailed boom assembly using specific aluminum tubing (e.g., BA, BB, BC, BD, BE) and brackets, and element construction with various aluminum tube sections (e.g., EA, EB, EC, ED, EE, EF) and traps like the _15 Meter Director Trap_ (TB) and _10 Meter Director Trap_ (T9). It also specifies the use of _NOALOX® conductive lubricant_ for telescoping sections and hardware to prevent galling. The manual outlines the feed system assembly, which includes feed-straps (FL1, FL2, FL3), tuning-tube insulators, and the matching network. It also mentions the optional X740 40-meter add-on kit, which requires a separate coax feed. Detailed diagrams and parts lists with metric equivalents facilitate accurate construction and ensure the antenna performs as specified.

Demonstrates the construction of a 144 MHz turnstile antenna, detailing its design for omnidirectional, horizontally polarized VHF operation. The resource outlines the physical dimensions and materials required, including specific lengths for the radiating elements and the use of _RG-58_ coaxial cable for phasing. It covers the assembly process, emphasizing the critical spacing and connection points to achieve the desired radiation pattern and impedance matching for the _2-meter band_. The article presents measured _SWR_ performance across the 144-146 MHz segment, showing a low SWR of 1.2:1 at 144.5 MHz, which is suitable for general VHF use. It compares the turnstile's performance to a 9-element Yagi, noting the turnstile's advantage in providing consistent signal strength from all directions without requiring a rotator. Practical application for local FM simplex and repeater operations is implied, offering a simple yet effective antenna solution for fixed or portable stations.

Unlocking the full multiband potential of the 225 Ohm elementary radiator in a folded monopole, dipole-like or turnstile layout, by Francesco Errante

17-Element Very High Frequency/Ultra High Frequency Log Period Dipole Array

TurboLog is a station management and logging program designed for amateur radio operators, providing robust database and logging functionalities. It features fully integrated support for controlling typical radio station equipment, including transceivers, packet radio TNCs, Morse and voice keyers, and digital mode terminals. The software also incorporates antenna switching capabilities and acoustic alerting, streamlining station operations for DXing and contesting. The program's utility extends to award tracking for entities like DXCC and IOTA, alongside comprehensive callbook and ham database integration. It supports log import and export, QSL label generation, and includes TNC drivers for packet radio. The trial version allows users to evaluate its extensive features before commitment, making it a versatile tool for managing complex amateur radio station configurations and operational data.

All types of Military Antennas, Law Enforcement Antennas, Mobile Radio Antennas, GPS Antennas, Satellite Antennas, WLAN/Wi-Fi/WiMax Antennas, Cell Phones, TV, HDTV Antennas available and sold

One point eight MHz to 30 MHz is the operational bandwidth for this 4:1 Ruthroff voltage balun, designed to interface an unbalanced T-Match network with a balanced antenna system. The project details the construction using a _T200-2_ powdered iron toroid core, tightly wrapped in PVC electrical tape for insulation, and wound with 17 double bifilar turns of 1.25mm enamelled copper wire. This outboard balun offers flexibility, allowing hams to trial various baluns based on antenna system and impedance characteristics, rather than integrating it directly into the tuner. The resource includes a schematic of the balun, a wiring diagram showing winding connections, and a table suggesting alternative toroid cores like the T80-2 or T400-2 with corresponding winding counts. Component sourcing is straightforward, listing items such as the _Amidon_ T-200-2 core, SO-239 connector, and a sealed polycarbonate enclosure from Jaycar. Performance evaluation was conducted using an _AIM 4170C_ antenna analyser, demonstrating efficient 1:4 voltage transformation across the specified HF spectrum. Further efficiency tests involved measuring RF power loss at various frequencies, revealing minimal loss—less than 0.7 dB from 3.6 MHz to 30 MHz, and only 2.0 dB at 1.8 MHz. These measurements, performed under ideal 50-ohm conditions, confirm the balun's effectiveness as a low-loss interface for multi-band antenna systems. The page also links to several other balun and unun projects, including 1:1 current and voltage baluns, and 9:1 voltage ununs, providing a broader context for impedance matching solutions.

G3TXQ study on coaxial cable demonstrate that it can reduce an element's length by something approaching the Velocity Factor of the cable

An online J-Pole antenna calculator that need just to input the frequency and calculates in inch size of each element

Deploying robust antenna infrastructure for both fixed and portable operations often requires specialized support structures capable of withstanding environmental stresses while providing optimal radiating element placement. SMC offers a range of solutions, including pneumatic masts and push-up masts, designed to facilitate rapid deployment and reliable long-term support for various antenna types. Their product line encompasses antenna mounts, poles, and complete antenna systems, addressing the critical need for stable and efficient RF communication. The company's offerings extend to HF antennas, including dipoles and _NVIS_ (Near Vertical Incidence Skywave) antennas, which are crucial for short-range regional communications on bands like 80m and 40m. These systems are engineered for durability and performance, ensuring signal integrity across diverse operating conditions. With over **65 years** of experience, SMC has established itself as a global manufacturer in this niche. Their product portfolio also includes antenna support towers, catering to more permanent installations requiring significant height and load capacity for multiple arrays.

A simple and awesome wire monoband antenna, very usefull for portable and dxpeditions usage, consist of two elements, a driver and the reflector. This endfed halfwave gives a very low take off angle and is very suited for chasing DX.

Presents a curated collection of newsletters dedicated to _Earth-Moon-Earth_ (EME) communications, primarily focusing on the 432 MHz band and higher microwave frequencies. The resource details various EME DX experiences and news contributions from operators like K2UYH (W6/PA0ZN), offering insights into successful moonbounce contacts and operational strategies. It serves as an archive of specialized content for those engaged in or interested in extreme weak-signal propagation via the moon. The newsletters provide practical information on achieving EME contacts, often including details on station setups, antenna arrays, and signal reports from challenging DX. For instance, operators might report achieving contacts over **750,000 km** round trip, demonstrating the feasibility of long-distance communication on UHF and microwave bands. The content differentiates itself by concentrating on the unique technical and operational aspects of EME, which contrasts significantly with terrestrial DXing, providing a specialized knowledge base for advanced amateur radio operators.

The resource presents a detailed schematic for constructing a dual-band vertical antenna, specifically designed for operation on the 2-meter and 70-centimeter amateur radio bands. It illustrates the physical layout, critical dimensions, and component placement necessary for successful replication. Key elements such as the radiating elements, phasing sections, and feed point are clearly depicted, providing a visual guide for radio amateurs undertaking a homebrew antenna project. The diagram specifies the lengths for the VHF and UHF sections, indicating how these elements are integrated to achieve dual-band functionality from a single coaxial feedline. It also implies the use of common materials readily available to most experimenters, focusing on simplicity and effectiveness in its design. The visual format of a GIF image ensures direct access to the construction details without requiring extensive textual interpretation. This schematic serves as a practical reference for hams interested in building a compact, efficient vertical antenna for local and regional FM communications, offering a proven design for immediate implementation.

A 2-meter Moxon beam antenna, designed for the _144 MHz_ band, is detailed, originating from a desire to participate in the PW 2m QRP contest. The design, based on a Moxon Rectangle, offers a compact directional solution for VHF portable operations. The author, G0KYA, constructed the antenna using readily available materials like 15mm plastic conduit for the frame and 1.5mm copper wire for the elements. Initial testing with an MFJ-259B antenna analyzer showed a **1.2:1 SWR** at 144.300 MHz, indicating good resonance. The antenna's compact size, approximately 70cm x 40cm, makes it highly suitable for portable QRP work, providing a significant advantage over an omnidirectional vertical. The project includes practical advice on element spacing and construction techniques, emphasizing ease of assembly for field deployment. Field results from a local hilltop demonstrated the Moxon's directional characteristics, allowing for effective nulling of local noise and improved signal reception from specific directions.

Similar to Tiny 2 but this three element direct connect antenna utilizes a reflector and a director to achieve gain.

SecondHandRadio.com provides a platform for the amateur radio community to buy, sell, and swap used, surplus, and obsolete electronics and electrical equipment. The site facilitates transactions for a wide range of items, including ham radio transceivers, test equipment, shortwave receivers, antennas, and vintage radio components like tubes. Users can place classified advertisements with photos at no cost, catering to individuals, radio clubs, and commercial dealers seeking to liquidate or acquire gear. The platform emphasizes ease of use with a straightforward sign-up process and no associated fees or commissions for listing or selling items. It positions itself as a primary resource for used electronics within the USA, fostering a direct connection between sellers and buyers without intermediary charges. The service supports various categories beyond amateur radio, extending to military radios and antique equipment, thus serving a broad spectrum of radio enthusiasts and collectors.

A 4 element addition for 10m to an existing 4 element yagi (ZX antennas)

Presents a QRP AM/CW transmitter project specifically designed for the 10-meter band, utilizing a crystal oscillator and a collector-modulated AM oscillator. The design employs a 2N2219(A) transistor in a Colpitts configuration, generating 100 to 350 mW of RF output power depending on the 9-18 Volt supply voltage and modulation depth. Frequency stability is maintained by a 28 MHz crystal, with fine-tuning possible via a Ct1 trimmer capacitor for approximately 1 kHz adjustment. The resource details the RF oscillator stage, implemented with a 2N2219 NPN transistor, emphasizing frequency stability and low power dissipation. It also covers the amplitude modulation stage, managed by a 2N2905 PNP transistor, which impresses audio information onto the carrier. Selective components (C3, C4, C7, C5) enhance voice frequencies within a +/- 5 kHz bandwidth, and modulation depth is controlled by R2 and R3. The project includes a 3-element L-type narrow bandpass filter (Ct3, L3, C10) to suppress harmonics and ensure a clean output signal. The project provides a complete schematic diagram, a comprehensive parts list including specific capacitor, resistor, and inductor values, and construction notes for the coils (L1, L2, L3). It also offers practical advice on enclosure requirements, suggesting an all-metal case or a PVC box with graphite paint for RF shielding. Operational parameters such as current draw (27mA@9V to 45mA@16V) and input impedance (50 Ohms) are specified, alongside guidance on antenna matching and the importance of a valid amateur radio license for 10-meter band operation.

The antenna is a VHF side is a 2m moxon, tuned on 145.825 MHz. The driven element of the moxon couples to a driven element for a 5 element 70cms Yagi, tuned on 436.5 MHz.

SWR (standing wave ratio), is a measurement of how efficiently your antenna system will radiate the power available from your radio. In simple terms, your radio would like to radiate all of its power, but can only do so if the other components cooperate

The ZS6BKW multiband antenna, an optimized variant of the classic G5RV, features a 102-foot (31.1 m) horizontal span and a 39.1-foot ladder line matching section. This design, derived by G0GSF (formerly ZS6BKW) in the early 1980s using computer programs and _Smith charts_, aims for improved SWR across multiple HF bands compared to its predecessor. Construction details specify Wireman 554 ladder line and #14 AWG THHN copper wire for the radiators, with precise instructions for determining the velocity factor (VF) of the ladder line using an antenna analyzer or dip meter, ensuring accurate physical length for the matching section. The radiator length is electrically 1.35 wavelengths for the 20-meter band, requiring careful trimming during tuning. Field measurements with an _AIM-4170C_ analyzer by KI4PMI and NC4FB demonstrated good SWR curves and bandwidth on 6, 10, 12, 17, 20, and 40 meters. The antenna was deemed unusable on 15 and 30 meters due to very high SWR, but an LDG AT-100PRO autotuner successfully brought 6 and 80 meters into tune. Contacts were made on 80, 40, 20, and 17 meters, including a **17-meter** contact to Spain. EZNEC models for 80-6 meters are provided, along with an AutoEZ model by AC6LA, which predicted good SWR for 80-10 meters. W5DXP's modifications for an all-band HF ZS6BKW are also referenced.

This is a plan for a 10 elements yagi antenna for 50 mhz

The _Italian VHF Beacons_ resource provides a detailed listing of active and QRT amateur radio beacons operating across VHF, UHF, and SHF bands within Italy. Each entry specifies the beacon's callsign (e.g., IQ1SP/B), operating frequency (e.g., 144.411 MHz), QTH locator (e.g., JN44VC), effective radiated power (ERP) in watts, and antenna configuration (e.g., Big Wheel, 4x Dipole, Yagi). This data is crucial for radio amateurs involved in propagation studies, equipment testing, and long-distance (DX) communication on these higher frequency bands, offering fixed signal sources for monitoring. This compilation, last updated in October 2005, serves as a historical snapshot of Italian beacon activity. For instance, it lists several 144 MHz beacons with ERPs ranging from **0.1W** to **10W**, and higher frequency beacons such as I8EMG/B on 1296.880 MHz and I3EME/B on 24192.132 MHz. The inclusion of QRT (Quiet Radio Teletype) status for many entries indicates the dynamic nature of beacon operations over time. Users can utilize this information to identify potential signal sources for band openings or to calibrate their receiving equipment against known transmissions.

About the clemens match for beam antenna, as an alternative to common gamma matching techniques

The SCOTIA Bandhopper, a multi-band mobile vertical antenna, offers a unique sliding coil design for rapid band changes across 10m to 80m. Drawing inspiration from the classic Webster _Bandspanner_, this design improves efficiency through near-center loading, theoretically achieving up to **2.25 times** greater radiation resistance than base-loaded counterparts. The antenna, extending to approximately 10 feet on 80m, utilizes a 5-foot fiberglass tube with an internal loading coil and a 57-inch tapered steel whip, allowing continuous tuning across bands without changing coils or whip sections. Field results from GM3VLB and the SCOTIA team, based on over 40 years of /M and /P operations, indicate the Bandhopper significantly outperforms shorter mobile whips. Its slim profile minimizes drag, making it suitable for sustained motorway speeds. The design incorporates a novel "fixed spring contact" arrangement for the variable inductance loading coil, with two sets of contacts for 10/12m and 15-80m. Construction details are provided, including materials like boundary marker poles and specific wire gauges, with an estimated build cost of **£20** or less, depending on junk box availability.