Many thanks for your help folks. I will have a look.

I am checking out the following one:

http://www.altered-state.com/cgi-local/reload.cgi?//www.ask.co.uk/ix.asp?q=how+do+I+measure+the+strength+of+a+rf&ac= none&xx=0&qid=E4DECE19AE4A2943B1E53A6D9AF1B77F&p=0 &s=1&sp=ix&fn=t&b=0&fo=2&r=10&io=4&fp=4&fr=1&url=h ttp%3A%2F%2Fwww%2Ealtered%2Dstate%2Ecom%2Ftrifield %2Frf%5Ffieldstrengh%2Ehtm&adurl=^/trifield/rf_fieldstrengh.htm

Cheers, Meeker