While mucking around last night, I ended up asking myself how i could find out what the attenuation of the TV antennas atop Sutro Tower would be. While trying to answer this question, I found out about Splat!
I haven't worked out the attenuation from Sutro Tower yet, but it did allow me to make this map of how signals from my home on the 6m band might get out.
Addendum: Worked out the Sutro Tower example. At 190Mhz, we get the following:
Summary for the link between KQED and HOME: Free space path loss: 107.37 dB Longley-Rice path loss: 129.46 dB Attenuation due to effects of terrain: 22.09 dB Field strength at HOME: 78.37 dBuV/meter Voltage produced by a terminated 50 ohm 0 dBd gain antenna: 1724.03 uV Voltage produced by a terminated 75 ohm 0 dBd gain antenna: 2111.50 uV Mode of propagation: Single Horizon, Diffraction Dominant
Addendum2: Doug Lung has a fairly nice introductory tutorial. There is also a chapter dealing with this in the Mapping Hacks book.