[TenTec] Orions SO2R in CQ WW RTTY

[Bill Tippett <btippett@alum.mit.edu>]

Hi Bob,

        Nice job in the contest!  Your comment below raises a
question I've had for some time.  Maybe N4PY has some ideas.

5B4AGN wrote:
>2.  Filter shape factor is really the only significant concern I had over
the weekend.  With b/w down at around 250 Hz the DSP shape factor is not far
short of 3:1 which really isn't good enough.  As a consequence, folks could
sidle up real close to Orion's beautifully clean signal and sit there inside
my passband causing me grief.  I spent way too much time over the weekend
inching up or down in frequency to avoid QRM from folks alongside.  This
leads me to the following conclusion:
FOR TOP NOTCH CONTEST GRADE RTTY USE, ORION'S DSP NEEDS TIGHTER SKIRTS.

        Carl N4PY measured the following in May 2003:

Filter       6 DB width     60 DB width    Shape Factor

100            150             440               2.9:1
250            240             470              1.95:1
500            510             820               1.6:1
1000           980            1160               1.2:1
1600          1580            1880               1.2:1
2400          2360            2500              1.06:1
3000          2930            3270              1.12:1
4000          3960            4280              1.08:1

Source:         http://dayton.akorn.net/pipermail/tentec/2003-May/033783.html

        But G3SJX of RSGB reported the following:

100            131             623               4.8:1
250            225             682               3.0:1
500            444             843               1.9:1
1000           965            1338               1.4:1
1800          1766            2151               1.2:1
2400          2364            2746              1.16:1
4000          3974            4362               1.1:1
6000          5236            6322               1.2:1

Source:  June 2004 RadCom review of Orion

        I've wondered about the large difference in shape factors
for narrow DSP filters and wonder if Carl has any ideas why.
I'm assuming both Carl and G3SJX set the roofing filter to
one much broader than the DSP so that they were not measuring
the cascaded effect.

        BTW, when someone sidles up close to me, I usually return
the favor by moving closer to them, just to make sure they can
hear me better.  ;-)  I normally out-hear them and they usually
go away after awhile.

                                                73,  Bill  W4ZV
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