The spectrum of an analog TV signal

When you're into Offset DX you need to know some basics about the carriers you can detect. Each analog TV signal consists of multiple signals. The strongest one is the main video carrier (the nominal frequency). But there are other lines in the spectrum which arrear periodically and much weaker. When DXing it's essential to decide whether a weak detected carrier belongs to a completely new station or is just a sub-carrier of a stronger one (often +/- 15625 Hz, with offsets appearing on 12m, 4m, 4p or 12p).

nominal offset

First let's look at the channel structure. Every station has a nominal offset. These have 1/12 steps of the line frequency. The line frequency is the line number * images per second. (see Wikipedia)