FM band undersampling
Why Use Oversampling when Undersampling Can do the Job? - Texas Instruments : “..If we use the sampling frequency less than twice the maximum frequency component in the signal, then it is called undersampling. Undersampling is also known as band pass sampling, harmonic sampling or super-Nyquist sampling. Nyquist-Shannon Sampling theorem, which is the modified version of the Nyquist sampling theorem, says that the sampling frequency needs to be twice the signal bandwidth and not twice the maximum frequency component, in order to be able to reconstruct the original signal perfectly from the sampled version.“
Justin Peng tweeted the result of his RX888 undersampling the FM band on https://twitter.com/fei666888/status/1363859596784267265
At my location the FM band stations are very strong and internal HF LPF of RX888 is not enough to cancel the FM band alias.
I need to add an external HF Low Pass Filter with higher attenuation of FM band. So I decided to bypass the internal filter always and to add externally LP or BP filters
I removed C52, L7, C55, L5 and made a wire jumper between C52-L7 and C55 - L5.
I soldered the removed component to an unused or ground pad so that can be used in future to reverse the modification.