The crystals will be different frequenices due to how radios work. The TX xtal should be on the frequency that you expect (ie 72.35MHz for channel 28). For the RX xtal it will be different to the TX xtal by whatever the IF (intermediate frequency) of the RX is. For a single conversion RX this is 455kHz and for a dual it is 10.7MHz (from memory could be different). Even though the xtals are a pair you need to make sure that you use the correct xtal in the RX or TX.