Really interesting thread so far. Tim I was getting those figures from an article I read here - http://urgentcomm.com/networks_and_systems/mag/designing_simulcast_networks_... "Analog FM systems on 25 kHz channels typically can withstand two relatively strong, equal amplitude signals with up to 150 microseconds relative delay before speech is unintelligible, according to Garry C. Hess in *Land-Mobile Radio System Engineering"* I have used radio mobile quite a lot. It might be time to ascertain my coverage. The only gripe I have with Radio Mobile is that it overestimates at low band VHF by default. UHF coverages are pretty accurate in my opinion. I've also used Splat, and still use Splat to overlay onto Google Earth. Do you change the strong signal margin on one site in Radio Mobile to 0dB/20dB for the 10dB difference, then plot the two together? Hayden