Just a comment on the mention of images in the passband. A way to deal with the image of a unwanted signal, is to make a wave absorption trap (rf notch filter) in the antenna tuner to the SDR receiver. You can tune real close to the desired signal in some cases and not effect the desired signal. But notch out the unwanted signal and reduce it's image.
And naturally the idea of a crystal filter in the radio hardware will help with some images, in that the narrow filter will block out of band signals.
