RE: channel no.
If you look at the rear of your transmitter, there should be a small round silver sticker that has the channel number and frequency on it, or you can pull the crystal and it will have a tag with the frequency as well as the channel. (channel 50, for instance, is 72.790 MHz)
AM Tx must use AM Rx, and Fm with FM. PCM is a type of FM, both Tx and Rx must be PCM.
Yes, your receiver has to match the frequency, the receiver crystal will also have a tag with the channel/freq. on it..............
UNLESS-- you have a radio system with a frequency synthesizer, which allows you to select a desired freq. The Tx and Rx still have to match.......
OR-- you have one of the new DSSS (Spread Spectrum) systems, which is on a totally different band than 72MHz FM. The Tx and Rx are matched to each other, and only work with each other, on any available frequency in the 2.3GHz band.