Wed, 14 Jan 2004 18:08:17 -0500, Bill W4ZV wrote:
>> Terry (and Rick), this brings up an interesting point. The
250 and 500 Hz filters DO have higher insertion loss so Ten-Tec
compensates for this by using an additional stage of amplification.
BUT this also causes the 3-5 dB DR degradation ARRL noted in their
Expanded Test Report (see note at the bottom of page 16) when using
the 500 Hz roofing filter.
One could easily add a simple (cheap) resistive pad at the output
of ones homebrew 4 pole filter to bring the level back down to that
expected by the receiver. In doing so, one might consider equalizing
the loss to that of the 250Hz filter, which has a couple of dB greater
loss than the 500Hz filter. Presumably, this would improve the
IMD degradation problem. Then, one could leave the 1000Hz filter
in place and put the new 600Hz filter in the 500Hz slot.
Also, Bill wrote:
>> The 250 and 500 Hz positions also use a slightly different IF
of 9.000750 instead of 9.001500 for the 1000 Hz and above positions.
The Inrad kit is actually for 9.000000 MHz as it stands unless you
make a special order (10 minimum). You could use the 9.0 MHz kit,
but you would have to use Orion's PBT to shift either 750 or 1500 Hz
depending on whether you wanted to put the filter into the "500"
position or the "1000" position, and you would likely lose one of
the CW passbands because of the limited range of PBT. I already
tried inserting my Inrad 400 in the 1000 position but recall only
UCW would work with the range of PBT adjustment.
Yes, this is the published spec for the TenTec filters. Inrad has
two 400Hz cw filters, one with 600Hz offset, the other with 750Hz
offset. TenTec has a provision to "tweak" the Orion to center the
inexact offset on individual narrow filters. Since this is a
software setting, it may be that an update of the Orion software
would even let 9.000000 filters be accomodated. Since Bill, as
a beta tester, apparently has the ear of the programmer, perhaps
this could be determined.
Of course, for those interested in my original post about creating
useful first IF filters for the OMNI VI, you would want to get on
board Bill's train for the special order, since the offset is
critical to make the passbands of the two IFs align.
BTW, will the kit include the four pins for mating with the socket?
Terry Zivney, N4TZ/9
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