Search results

Occasionally errors are made regarding core selection. This especially includes baluns, where on occasion some very strange ideas surface.

This resource details the construction of a versatile CW/QRSS beacon, designed around a Microchip _PIC16F84_ microcontroller. The project provides a flexible platform for transmitting either standard CW or very slow QRSS signals, making it suitable for LF, VHF, UHF, and SHF applications. It supports two distinct messages, each configurable for speed (from 0 to **127** WPM for CW, or up to **127** seconds per dot for QRSS) and repetition within a six-phase sequence. The core functionality relies on the PIC's EEPROM, which stores all operational parameters, including message content, transmission speeds, phase configurations, and relay control settings. This design allows for parameter modification directly via programming software like _ICProg_ without altering the main program code. The project includes a detailed schematic, a component list, and an explanation of the EEPROM memory mapping for messages, speeds, phase settings, and inter-phase delays. General-purpose outputs (OUT1, OUT2, OUT3) provide dry relay contacts for external control, enabling functions such as power switching, antenna selection, or frequency changes. A 'TRIGGER' input facilitates controlled starts or continuous free-run operation. Sample EEPROM configurations illustrate how to program specific beacon sequences, including message content and relay states.

Demonstrates the essential steps for winding **toroidal cores**, a fundamental skill for amateur radio operators engaged in homebrewing and kit building. It addresses the critical aspects of selecting the correct core material and wire gauge, emphasizing the importance of precise turn counting and consistent winding tension to ensure optimal circuit performance. The resource details methods for preparing the wire, including techniques for safely removing enamel insulation from leads using flame, sandpaper, or a solder pot, and provides guidance on tinning the exposed wire. Explains the process of mounting the wound toroid onto a printed circuit board, highlighting the need for careful lead placement and secure soldering to prevent shorts and ensure mechanical stability. It also offers a practical formula for calculating the required wire length based on the desired number of turns and the specific **toroid** size, referencing common core types like T-50 and FT-240. The guide stresses the importance of verifying the inductance of the wound component, often using an inductance meter, to confirm it matches design specifications. Provides practical tips for handling multi-filar windings and managing short lead lengths, which can be particularly challenging. It underscores the necessity of meticulous attention to detail throughout the winding and installation process to achieve reliable and efficient RF circuits.

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.

Manufacture high quality low cost powder cores with a wide selection of shapes

A synthesized 2.3 GHz Amateur Television (ATV) transmitter design, conceived by Ian G6TVJ, is presented, targeting broadcast-quality video performance on the 13cm band and extending up to 2.6 GHz. The core of the design utilizes a commercial Z-comm Voltage Controlled Oscillator (VCO) that tunes from 2.2-2.7 GHz, providing a +10 dBm output and simplifying RF alignment. This VCO's stability, originally intended for narrowband applications, readily accepts high-frequency video modulation, contributing to the transmitter's robust performance. The exciter stage, incorporating a Mini Circuits VNA 25 MMIC amplifier, boosts the signal to +16dBm, while a Plessey SP4982 prescaler divides the output frequency for the synthesizer. The synthesizer employs a Motorola MC145151 CMOS parallel IC, favored over the common Plessey SP5060 for its superior video modulation characteristics and ease of programming without microprocessors. This choice addresses issues like LF tilt and distorted field syncs often seen with SP5060 designs, particularly when operating through repeaters or over long distances. The MC145151 divides the signal further, enabling precise frequency stepping, with programming handled by EPROMs for channel selection and LED display. The loop filter network, critical for video integrity, was developed through experimentation to prevent the PLL from reacting to video modulation, ensuring a clean transmitted picture. The transmitter incorporates a Down East Microwave commercial power amplifier module, delivering approximately 1.6W output, driven by the exciter through a 3dB attenuator. Construction involves surface-mount SHF components on micro-strip lines etched onto double-sided fiberglass board, housed within a tinplate box. The design boasts no AC coupling in the video path, preserving low-frequency response, a common failing in other ATV transmitters. Performance tests with a 50Hz square wave revealed no LF distortion, and a calibrated "Pulse & Bar" signal showed a near 100% HF response, demonstrating its capability for high-quality ATV transmissions.

A 20-meter window frame stealth antenna, based on a design by _PD7MAA_, utilizes a single 620cm wire loop for discreet installation. The feeding mechanism employs a _4C65_ toroidal core, where the antenna loop functions as a single-turn secondary, and the feedline wraps twice. Tuning is achieved via a 30cm twisted wire stub, allowing for SWR adjustment within the 20m band. This design is specified for QRP operation, with a maximum power limit of **25 Watts** to prevent core saturation or arcing. Wire selection recommendations include thin, insulated copper wire (0.75mm to 1mm) for blending with architectural elements. The guide focuses on practical construction steps for a low-profile 14MHz antenna.

WSJTX-Controller-v2, or Otto, functions as an assistant for the WSJT-X amateur radio program, specifically designed to enhance operational efficiency for weak signal digital modes. The software automates several key tasks, including call management, prioritizing DX stations based on user-defined criteria, and optimizing frequency selection within the WSJT-X interface. It requires a modified version of WSJT-X to function correctly, integrating directly with its core processes to provide augmented control. Otto supports various digital modes, facilitating auto-logging of contacts and generating specific alerts for desired stations or conditions. It is engineered to streamline the workflow for operators engaged in DXing and general weak signal communication, offering features like automatic CQ responses and intelligent band monitoring. The utility is not compatible with certain other amateur radio software and is explicitly noted as unsuitable for contest operations or the WSJT-X Hound mode, indicating its specialized focus on non-contest DX and casual operating. The project's GitHub repository provides the source code and documentation, allowing users to review its implementation and contribute to its development. The software's design emphasizes automation to reduce operator intervention during routine digital mode operations.

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.

Chokes and isolation transformers are essential for receiving antennas to mitigate common mode current, which induces noise and interferes with signal quality. Common mode chokes, formed by winding feedline through ferrite cores, block unwanted current effectively. Proper selection of core material and winding turns ensures resonance near the operating frequency, reducing interference. Isolation transformers further minimize interference, crucial for multi-transmitter stations.

The resource details the construction of a J-pole vertical antenna specifically engineered for motorcycle mounting, addressing the common issue of interference with top cases. It outlines the fabrication process, beginning with an aluminum angle bracket for secure attachment to the lateral support, followed by the creation of the antenna's base from an 8mm threaded rod bent into a U-shape, approximately **40mm** wide. The article specifies the precise method for coaxial cable connections using eyelets and 3mm screws, ensuring robust contact. Further construction steps involve fitting a 10mm aluminum tube onto the threaded rod, with a screw securing the radiating element and establishing core contact. The design prioritizes mechanical stability against vehicle vibrations over fine-tuning SWR with sliding collars. Initial testing yielded a _SWR_ of **1.2** across a significant portion of the band, with improvements noted by optimizing the coaxial braid contact point near the support bracket. The document provides practical insights into material selection and assembly, emphasizing durability for mobile operation. It concludes with aesthetic options, allowing the builder to paint the antenna or retain its natural aluminum finish, making it a functional and adaptable solution for UHF motorcycle communications.

Demonstrates the construction of an active loop converter specifically designed for the Low Frequency (LF) bands, addressing common localized noise interference in LF reception. The design integrates a sharply tuned circuit and a tuned loop antenna, utilizing the loop as the sole tuned inductive element. By applying positive feedback, the converter significantly increases the loop's effective Q, achieving factors between 1000 and 2000, which sharpens tuning and reduces noise. The circuit employs an _NE602_ mixer stage, feeding its output to an HF receiver, with a crystal-locked local oscillator at 4 MHz. A 20-turn, 0.8-meter square loop antenna with 500 uH inductance is detailed, connected via 2 meters of figure 8 flex cable. The converter offers three selectable frequency bands: 195-490 kHz, 150-220 kHz (including the New Zealand amateur band), and 128-160 kHz (covering the European amateur band). Performance measurements indicate an effective 3dB bandwidth of approximately 100 to 200 hertz at 200 kHz. The article provides insights into component selection, including an _LF353_ op-amp and a trifilar wound transformer on a ferrite core. Sensitivity figures are presented, showing 7.5 uV of converted output per 1 uV/meter signal strength into a 50-ohm load, or 37.5 uV into an _FRG7_ receiver, highlighting its capability to extract weak signals from noise.