The US Institute for Telecommunications Science (ITS) has published a well-known model for radio propagation commonly referred to as the Longley-Rice model. The input of the model includes environmental, system, and statistical parameters. The output is the predicted path loss between units.

Using this model, together with data from national mapping agencies overlaid on terrain data from NASA, it is now possible to deliver a map of your Target Service Area, with expected signal strengths. Typically a house portable will give useful reception in the white and red areas, whilst a car, or house with an external aerial will be served in the yellow and green areas also.

 
Corby FM – 25W to stacked dipole

This is also a great way to potentially predict your estimated caption area for any RSL project you maybe considering. It's ok to assume you may reach the town 5 miles away but it would be better if you knew you actually would.

For our standard service, all that we need to produce your maps is information about the location of the transmitter (postcode or exact latitude/longitude is better), the power output and the antenna details. The FM broadcast band and standard receiving equipment is assumed. Our extended service can produce maps for other frequencies, other polarisations, multiple transmitter sites, examination of potential buildings effects or point to point path checking (useful before you commit to doing that Outside Broadcast !)

Borrowash FM to Draycott, 4km SE