[TenTec] Orions SO2R in CQ WW RTTY
Bill Tippett
btippett at alum.mit.edu
Mon Sep 27 17:18:08 EDT 2004
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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