Image Frequencies
From The RadioReference Wiki
Images
An image is a false signal received on a frequency that does not actually exist. For a detailed description of how and why this occurs see the link below.
700 MHz
Many people can receive control channels, repeater outputs, etc. in the upper end of the 700 MHz band around 790-800 Mhz. These are images.
The 700 MHz band plan is as follows:
764.000000-775.996875 Base (repeater outputs, mobile talk-around) 776.000000-805.996875 Mobile (repeater inputs)
The Narrowband Public Safety band is:
769.003125-774.996875 Base 799.003125-805.996875 Mobile
If you are hearing control channel data or repeater outputs in the 776-806 MHz range they are images.