![[picture of takeoff]](qth.gif)
The image below, generated using wonderful software which accesses the UK topographic database, illustrates my problems with takeoff from my home QTH. The image shows the Isle of Wight, the Solent to the north, and the mainland in the upper third of the frame. The sea is dark blue, and land rises from lighter blue, through green, to orange for the highest. My QTH is marked with a white spot. Here is a large image containing topographic information for most of Europe (from central Spain and Italy up to central Norway, and Portugal to the Balkans), derived from USGS EROS data.
To the northern quadrant (from about 315 to 345 degrees), my takeoff angle is close to zero degrees, but at its worst, to the east (around 90 degrees) it rises to nearly 10 degrees. Slightly less bad takeoff angles are around 120 (to Italy, I) and 210 degrees (Spain, EA), but even then they do not fall below 5 degrees.
It is often stated that takeoff angles required for sporadic E propagation are relatively high, i.e. more than 10 degrees, so this hill-locked site should not be too disadvantageous. But if you are looking for further DX, this does not hold good: for instance, single-hop Es beyond 1400 km has a radiation angle of less than 5 degrees (see figures on p. 193 ff of Kenneth Davies, op. cit.). Sometimes you can actually enjoy an obstruction (refractive) enhancement to propagation, where refraction from the top of the obstruction results in stronger signals at lower angles than would otherwise be expected. Whilst this may have happened on some occasions, I don't think it is the rule, for me at least.
For tropo, the picture is rather worse. Getting into a duct, for instance across the Channel, is very unlikely, as my radiation to the south will reach the Channel at fairly high elevation and heading rapidly upwards. It is thus unlikely to be able to enter such low-level ducts (below 1-2 km above sea level) at a low enough angle of incidence (less than 1-2 degrees), although refraction might sometimes help overcome this.
Non-ducting tropo (NDT) really does require a low angle of takeoff to achieve good DX, or the radiation will quickly attain high altitudes and fail to achieve any significant common volume (these issues are discussed more on the NDT pages here). I am currently performing ray and beam tracing to investigate how I managed QSOs with northern Spain (EA) using NDT, and some early results are shown on the NDT pages.
Topography of my QTH
For the record, my IARU locator is IO90JO, my WAB square is SZ58, and the Isle of Wight has the IOTA designation of EU-120. I am a member of the UK Six Metre Group, the RSGB, and the RNARS. You are very welcome to send QSL cards via the bureau (RSGB) or direct to me: e-mail me for my full postal address. If you ever want a sked, or are coming to the Isle of Wight, then don't hesitate to get in touch please.
Last updated 5 Apr 1999
Howard Oakley
Mail howard@quercus.demon.co.uk