Separating the AM and QAM components in PAL signal demodulation
There's a trick that is used in NTSC that I believe also applies to PAL.

If you look at the fine detail of the spectrum of the luminance signal, you find that most of the energy is concentrated at multiples of the horizontal sweep frequency, with relatively little energy in between these peaks (this energy represents diagonal edges in the image, which are relatively rare). There is a similar pattern in the details of the chrominance signal. Therefore, the color subcarrier frequency was carefully chosen to place the peaks of its power spectrum between the peaks of the luminance spectrum.

The filters that can separate this information into two separate streams again are called "complementary comb filters". You create a comb filter for the luminance signal by delaying it by one horizontal line period and adding it to the original signal. You then subtract this filtered signal from the original signal to get the complement signal, which contains primarily the chrominance signal (which you subsequently bandpass filter to the appropriate range of frequencies).