Power/Gain vs Height

This page will demonstrate that well known phrase "height is king".

The next 3 prediction maps (key to colours at bottom of page) are based on a 2m dipole aerial at my QTH being fed with 10w and then the signal level that would be received by a mobile at NGR SO95008010 just south of Stourbridge. The only difference is aerial height above ground. This first map shows the signal coverage with the aerial 5m above ground level. The signal received at the mobile is shown as -73dbm (approx. S9). 

This second map shows the aerial raised from 5m to 10m above ground level, it doesn't look too much different from the first map, apart from a bit more colouring, however the signal received by the mobile has gone up by 17db from -73dbm to -56dbm (approx. S9+20). There are other ways to get this level of signal into the mobile at 5m AGL, you could turn the power up from 10w to about 450w or you could put up a huge 10dbd gain colinear and run about 45w into it. Whichever option you choose the dipole at 10m will generally outperform both of them.

Finally just to see the result lets jack the dipole up to 50m above ground (totally impractical for 98% of us i know). It's interesting to see that the signal received by the mobile has only gone up by 3db to -53dbm but further a field the map has filled with colour and signals are way up. The extra height close in will always have less effect and if the aerial were to go up very high the signal may even go down!

  S5 = Turquoise Blue  S9 = Yellow  S9+20 or more = Red