https://wiki.oarc.uk/ 2026-04-30T01:50:54+00:00 https://wiki.oarc.uk/ https://wiki.oarc.uk/_media/wiki:logo.png text/html 2024-11-04T18:29:31+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.oarc.uk/hf:antennas?rev=1730744971&do=diff Antenna Systems Antenna Types The Simple Dipole A simple dipole can be created from any piece of wire you have lying around. A dipole will normally be a half wave length for the band you are intending to work on. A dipole has a characteristic impedance of 73 ohms, though hams normally ignore this since it's fairly close to 50 ohms. text/html 2025-06-16T20:07:02+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.oarc.uk/hf:blackout?rev=1750104422&do=diff HF Blackouts and Amateur Radio High-Frequency (HF) blackouts occur when solar activity causes sudden disruptions in the Earth’s ionosphere, particularly affecting radio waves between approximately 3 to 30 MHz. These disruptions are primarily triggered by powerful solar flares, releasing intense X-ray and ultraviolet radiation that rapidly ionizes the D-layer of the ionosphere. text/html 2025-06-18T07:26:32+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.oarc.uk/hf:solar-terrestrial-data?rev=1750231592&do=diff Solar Terrestrial Data From time to time you might come across an image like this, like those published at n0nbh.com. [Click to add Solar-Terrestrial Data to your website!] The above is LIVE solar-terrestrial data. Solar-terrestrial charts are used to evaluate radio propagation conditions. TL;DR Quick Interpretation Tips Here is a bit longer guide on how to interpret them. text/html 2025-06-19T08:17:37+00:00 Anonymous (anonymous@undisclosed.example.com) https://wiki.oarc.uk/hf:transmission-lines?rev=1750321057&do=diff Transmission Lines Why is coax unbalanced? The Private Life of Coaxial Cable BBC White Paper 126 which explains much about coaxial cables. //There is mathematics//