Looking at some articles on the topic of group delay in SSB crystal filters there were demonstrations of the transistion of the signal in a filter being phase shifted by 90 degrees when analyzed on a scope. And this was a saort of worse case scenario I believe. I can not say that the human ear would pay much attention to this but it is something that those of us who are considering a hybrid radio system might want to study since anything that can alter the phase of our signal in the i.f. section might not be good for the detection of the I/Q signal. Meaning excessive group delay. And in a wider filter there might be modulation of the sidebands together or some other strange effect that can occur if there is phase shifting and phase distortion occuring? And the article mentioned that this is one of the effects of excessive group delay. So the idea of using a wide band crystal filter is something we might want to study to find out what sort of delay characteristic they have. I might speculate that a wide band crystal filter would not have allot of delay. But that would have to be looked up to prove. Filters then with allot of poles would have to be looked at for the amount of delay they have as compared to lesser pole filters. At least thats my recollection of things and its been along while. And so it is an interesting thing to ponder no doubt, and worthy of study. It is interesting nontheless to want to know what you can about this. But I know that some of this was also about the Hilbert transformer and as for that, thats the arena of the software experts. Next to this topic is another similar one of the noise figure of the hardware which is something I know I have to brush up on here. http://images.vertmarkets.com/CRLive/files/Downloads/8B3B882E-B579-11D4-8C77-009027DE0829/rfwb40a.zip This mile long link is for a file called "RF Workbench" which analyzes the noise figure of grouped rf devices. It is a MSDOS based applications but a colorfull and artistic one that you will like. It plots a nice graph.
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