Helix Antenna for 137 MHz
Build a 137 MHz Quadrifilar Helix Antenna for NOAA weather satellite reception.
Description
Presents a detailed construction guide for a Quadrifilar Helix Antenna (QHA) optimized for 137 MHz, specifically for receiving weather satellite transmissions. The resource outlines the author's experience building previous QHA designs, highlighting challenges with tuning and nulls, and then focuses on a refined design by John Boyer, documented by Steve Blackmore, which proved easier to build and yielded superior reception.
The guide provides precise element dimensions, including 1.5m of 32mm PVC pipe for the mast and 8mm soft copper tubing for the helix elements. It specifies lengths for horizontal tubes (190mm, 90mm) and helix elements (903mm, 1002mm), along with instructions for drilling, assembly, and forming a balun by wrapping RG58 coax around the mast. The text emphasizes critical steps like ensuring elements are square and twisting in the correct direction to avoid phase issues.
It includes references to original QST articles by Buck Ruperto (W3KH) and the WxSat program for decoding satellite transmissions, contextualizing the antenna's purpose. The article concludes with a sample NOAA 12 image from September 1998, demonstrating the antenna's reception capabilities.