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An Attic Coaxial-Cable trap dipole for 10, 15, 20, 30, 40, and 80 meters

A new perspective on the analysis and design of this popular antenna element. By Karl-Otto Muller, DG1MFT

This page describes the design and construction materials W8WWV used to build a coaxial cable trap. A coaxial cable trap is a parallel resonant circuit that is usually inserted in an antenna element to enable multiband operation.

This improved multiband trap dipole introduces a new trap design and a change in trap location. The antenna features double-coaxial-cable-wound traps having lower reactance and a higher quality factor (Q) than earlier coax-cable traps by W8NX

The 30/40 meter **vertical antenna** project by IK4DCS details the construction of a shortened, self-supporting design, reaching a total length of 5 meters. The antenna incorporates a linear loading section and a coaxial cable trap for 30 meters, based on the "Antenne Volume 2°" text by Nerio Neri (page 223). The design uses six radials, three for each band, positioned at approximately 90° inclination and at least one meter above the roof or ground, connected via a 1:1 balun at the feed point. Mechanical construction utilizes aluminum tubing, with a 2.30-meter primary radiator section (30 mm diameter) joined to a second part using a Teflon insert and a PVC sleeve for rigidity. The linear load, approximately 3.70 meters long, accounts for a 30% physical shortening of the quarter-wave element. A capacitive load, made from three 50 cm radials, is integrated into the 40-meter top section for fine-tuning. Final adjustments involved radial inclination for 40 meters, as initial testing showed increased SWR and interference on 30 meters due to nearby resonant structures. The author emphasizes the importance of clear space for optimal performance and provides drawings and photos to clarify the build process.

The Coax trap program computes design parameters for the construction of coaxial traps for HF usage. Typically these are constructed from PVC tube and RG58/59 coax

Over 70 international contests are supported by YPlog, a Windows-based logging and radio control program designed for amateur radio operators. This software integrates with various digital mode applications like _WinPSK_, _HamScope_, and _MMTTY_, facilitating partially automated log entry for modes such as PSK31, CW, and RTTY. It provides comprehensive logging capabilities including QSL label printing, beam headings, and dup-checking, alongside award tracking for DXCC, ITU/CQ zones, IOTA, Grid Locators, and Counties. The program offers advanced contesting features, including multi-multi or multi-2 networked operations with automatic log data sharing, multiple Cabrillo submission formats, and configurable CW keyboard layouts. Device support extends to TR-compatible CW keying, SO2R control with Top-Ten devices like the DX-DOUBLER, and internal W9XT digital voice keyer integration. YPlog is notable for its support of the _OK1RR DXCC_ country resolution files, providing a robust historical DX compendium. Beyond logging, YPlog includes two freeware utilities: one for computing design parameters for coaxial traps and another for displaying and printing azimuth and Mercator maps from the operator's QTH. The software runs on Windows 95/98/ME/NT/2K, with a recommended screen resolution of 1024x768. Registration costs **$50.00 US** to unlock all features, including full contesting capabilities and rotator control.

The 6 Band Inverted L Antenna MK3 is a versatile multiband antenna designed for amateur radio operators. This antenna covers 160m, 80m, 40m, 20m, 15m, and 10m bands, making it suitable for a wide range of HF communications. The design is based on a W3DZZ configuration, incorporating traps for optimal performance. The MK3 version features a sturdy 5/8th CB mast, replacing the original timber mast, which enhances durability against harsh weather conditions. The antenna's construction allows for effective operation, particularly on the 40m band, where it has been successfully used to contact distant locations including ZL, VK, and Antarctica. Constructing this antenna requires careful attention to detail, especially regarding the radials and grounding. The traps resonate at specific frequencies, and additional resources are available for building coaxial traps. The antenna is designed to work efficiently without an ATU on the lower bands, while higher bands may require tuning. This project is ideal for both beginner and intermediate operators looking to enhance their station with a reliable multiband antenna.

Testing and comparison of traps and trap antennas

The problem with making your own trapped HF antennas is usually getting the coaxial traps tuned to frequency.

A trap on the coaxial cable, also known as choke, helps to eliminate the sneaking of the reflected RF- energy to the shack. The trap can be made from the coaxial cable that feeds the antenna

Tuning HF Coaxial Antenna Traps

The problem with making your own trapped HF antennas is usually getting the coaxial traps tuned to frequency. This article explains a method using a RF signal generator at +10dBm output into the coaxial trap.

A document that will guide you on Coaxial-Cable trap optimization process to gain on global antenna performance and on increasing effective bandwidth.

This document provides comprehensive guidance on modeling and constructing multiband dipole antennas using traps. It addresses common segmentation issues in EZNEC modeling software, recommends optimal segment lengths for trap models, and compares trapped dipoles with paralleled multiband dipoles. While trap dipoles are significantly shorter, they exhibit lower gain and narrower bandwidth. Detailed instructions for building weatherproof coaxial traps include material lists, construction steps, and tuning methods. The guide notes that properly constructed coaxial traps introduce only minimal signal loss (0.6 dB) while offering practical multiband performance in a compact design.