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There are many different types of propagation studies, but usually the most helpful are the Talk Back or Talk In study.

 This type of study shows the physical locations where there is sufficient signal strength so mobile or portable units can theoretically "talk back" to the main base station or repeater.  Because the characteristics of mobiles and portables vary as to power output and antenna placement and gain, you should have BOTH a Mobile Talk Back, AND a Portable Talk Back study if both mobiles and portables are going to be used in the system.

Another type of propagation study is the Talk Out or Field Strength study.  This is a study that shows the geographic areas that the base or repeater transmits sufficient radio-frequency (RF) energy to be received by the mobile and portable units.

Ideally, your Talk Out and Talk Back studies should be balanced.  That is, your repeater or base shouldn't cover much more area with its signal than your mobiles and portables can talk back from.  Too much extra, and you are not only wasting money in excess equipment, you are causing more interference to other users than you should, and you could be causing additional interference to YOURSELF as well.

A Terrain Study also helps you to understand a propagation study.  The terrain - it's hills, mountains, rivers and other features have a strong impact on your coverage. 

The colors of the study can be adjusted to show the differing levels of field strength.  For ease of use and understanding, unless instructed otherwise, we use the following color plan:

Dark Yellow: Signal strength to about -69 dbm
Light Yellow: Signal strength between -70 to -107 dbm
Dark Grey: Signal strength between -107 to -117 dbm
Light Grey: Signal strength between -118 to -123 dbm

A signal strength of about -107 dbm is generally considered the minimum acceptable field strength for adequate service, although depending on the equipment, location and other factors, you may be able to successfully talk in a area that has much a much lower signal strength (a higher negative dbm number).

Propagation Example Set 1

VHF - West Virginia

Click on the thumbnail for full size.  Most files are about 300kb.