Poor frequency stability in a receiver usually originates in the:

The local oscillator (LO) is the primary frequency-generating circuit in a superheterodyne receiver. Because the receiver's operating frequency is directly derived from the LO, any drift in the oscillator's frequency will cause the entire radio to drift. Power supply variations can directly alter the capacitance or operating characteristics of the components inside the local oscillator, causing it to shift in frequency. While the RF amplifier, mixer, and detector are crucial for processing the signal, they do not generate the base tuning frequencies and therefore do not dictate the receiver's frequency stability.