[TenTec] INRAD Filter Question

[btippett@alum.mit.edu (Bill Tippett)]

K0CQ wrote:
 >
Inrad makes claims for steeper skirts and squarer shoulders than the
similar TT filters. When passing static and high speed CW and clean
signals to a DSP, those are not necessarily good characteristics because
they (squarer shoulders and steeper skirts) are generally accompanied
more rapid deviations from linear phase delay that damages rapidly
changing signals.

         There is actually not much difference between Inrad and Ten Tec
filters.  Thanks to Roger K9RB who forwarded actual data from Ten Tec
on the 217, 218, 219 and 220 from here:
http://www.qsl.net/tentec/manuals/217.pdf

Here are the comparisons (Inrad data from:
http://www.qth.com/inrad/tentec_menu.htm

Filter  6 dB BW Shape Factor
TT217   500             2.0:1

IR759   455             2.1:1

TT218   1800            1.8:1IR761      1913        1.7:1

TT219   250             2.4:1
IR760      315          2.2:1

TT220   2400        1.7:1

         Still seems odd to me that TT switches the optional 500 and 250
roofing filters at 370 and 190 Hz, yet they switch the standard 2400
and 6000 at 2390 and 5990 Hz respectively.  I wonder why?

                                                 73,  Bill W4ZV