i read it in most books that a high injection side local oscillator is preferred over low injection side at mixer stages in heterodyne receivers.this is not only the case with AM signals (where variation ratio becomes very high)but even at rf signals having freqs in GHz.
can anybody pls explain why is the case???????
Also, mixers generate output tones that are (M x IF) +/- (N x LO). By allowing the choice of low side or high side LO, you can pick the one where the least amount of unwanted spurious signals are generated. (just keep in mind that some types of modulation might get reversed, since you are ADDING or SUBTRACTNG the IF, depending on the math).