Knut DK5AD/OE2BZL/OE2G wrote:
>I have now ordered the Inrad
600HZ filter and hopethings are better with it. Unfortunately I could
not find any data or graphs of the TenTec 500 or 1000Hz filters so I
would be able to compare them with the Inrad 600Hz filter.
What filter were you using when you had the problem?
Any filter in the Orion "500" position will have worseIMD performance than
the stock 1000 Hz, apparently
because of the extra amplification stage used for the
500 and 250 positions. The Inrad #762 600 Hz improves
the IMD performance of Orion using the 1000 Hz by about
6-7 dB at 2 kHz and almost 10 dB at 1 kHz spacings. It
is definitely the best to use in contests. More info:
BTW, the shape factor of the Inrad 600 and Ten-Tec 1000
are much worse than the Ten-Tec 500, however rejection
beyond about 30 dB down is not a major concern for a
roofing filter followed by DSP filters. From my memory:
Filter 6 dB BW Shape Factor
500 550 2.1:1
600 640 4.7:1
1000 1070 4.7:1
The 600 looks much worse than the 500 on paper but
that does not take into account the IMD degradation
apparently caused by the amplifier following the 500
stage. The Inrad #762 MUST be inserted into the 1000
position to work properly.
More info on roofing filters here (see page 3 re Orion):
With the Inrad 762 installed, Orion's IMD and BDR
are much better than a Sherwood-equipped R4C.
...and this data is using only the 1000 Hz filter, not
the Inrad 762 which is much better. If you are seeing
otherwise there is simply something wrong with your rig.
73, Bill W4ZV
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