Image Frequencies

Images

An image is a false signal received on a frequency that does not actually exist due to poor receiver design.

For a detailed description of how and why this occurs see the article at Radio-Electronics.com linked at the bottom of this page.

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 of 800 MHz stations. Scanners manufactured by GRE are particulary susceptible to 700 MHz images.

Many older scanners used a dual conversion receiver with a 10.7 or 10.8 MHz IF. With these types of receivers images can be received at 21.4 or 21.6 MHz higher than the actual frequency.

700 MHz

The 700 MHz band is split into two 30 MHz wide sections. Mobiles use a +30 MHz offset.

764-776 - Base (repeater outputs, mobile talk-around)
776-806 - Mobile (repeater inputs)

The Narrowband Public Safety allocations are:

769.003125-774.996875 - Base
799.003125-805.996875 - Mobile

If you are receiving control channel data or repeater outputs in the 776-806 MHz range (in the US or Canada) you are receiving images.

Links

• Radio receiver image response and image rejection