Latest 432MHz DX spots

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432MHz can be a very frustrating band. Long distance radio communications are possible via Tropo Ducting. This mode of propagation requires specific weather patterns to create the conditions (temperature inversion) needed for the duct to be created; basically a steady high pressure system is required 1025mB plus and light or no winds. The duct that is formed is a warm air layer sandwiched between colder air layers and can be likened to a pipe inside which signals are trapped, but if there are mountains in the way they will block this. Fog can be an indicator to such conditions.

Tropo ducting occurs when there is a temperature inversion. This often occurs when there is fog and steady high pressure over a number of days. The greater the size of the inversion duct or 'pipe' the lower the frequency that will be trapped within. This means in practice that as the inversion gets larger microwave frequencies 1296MHz will be supported first, then UHF 432MHz, then lastly VHF 144MHz. An inversion of around 300feet (91m) depth is required to support 432MHz signals.

When I lived in London, which is fairly flat and has a good view to the horizon, I could work Switzerland with 10watts and an ex-military flat phased array of 16 dipoles and a reflector panel. Since moving to the Lake District in 1990 the furthest distance that I have achieved has only been around 200km via Tropo scatter. The mountains simply block all Tropo Ducting for me as I live in the valley floor. In 2006 there was a fantastic Tropo Ducting opening to Scandinavia which we could hear from the top of the Pennines 20km to the East of my QTH, but as soon as you drove slightly down the hill towards my home they all disappeared.

There are other methods of achieving long distance communications on this band such as Amateur Satellites or Moon bounce (EME), but this can get very complicated and often may require an elevation rotator and extensive antennas. Signals on 432MHz are much weaker than on 144MHz. It is however a good band for mobile repeaters using FM and the UK has an extensive network in most areas.