In article , Patrick Turner
wrote:

John Byrns wrote:

7. It has been suggested that using a 2 MHz IF frequency would allow
wider bandwidth than the standard 455 kHz IF frequency. I fail to see why
this should be true.

Because for the same Q value, the pass band would be 4 times wider

Where is it written that the same loaded Q must be used for both filters?
If you can change the center frequency, why can't you change the loaded Q?

Within reason, for bandwidths typical of audio
receivers, you should be able to build a filter at 455 kHz that has
effectively the same response as a 2 MHz filter. There is no need to
throw out the 455 kHz IF just to get wide bandwidth.

Its difficult to make a 455kHz typical old IFT produce a nice flat topped
20 kHz wide BW. Its either pointy nosed, undecoupled, or flat topped, critical
coupled,
or over critical or rabbit eared.
I have tried all that.

So you have tried all that and rejected the "pointy nosed", "flat topped",
and "rabbit eared" response curves. I am left to wonder what sort of
response curve you were looking for? Why not settle for a nice "flat
topped" response curve and be done with it?


Regards,

John Byrns


Surf my web pages at, http://users.rcn.com/jbyrns/