AE5X:
>I'm surprised that so many roofing filters (and the K3 itself) have been
designed and offered for sale before the specifications are known/posted.
Seems like the reverse order would have been more appropriate.
I was also concerned about so many filters until I realized
Elecraft has actually leveraged the Inrad 7XX series of filters
offered for the 8.215 MHz IF of the FT-1000 family. I suspect
they may even use the same mechanical configuration, so hopefully
they have not invested R&D and inventory resources in providing
the large number of 8-pole filters.
http://www.qth.com/inrad/ft1000mp.htm
The 5-pole and variable BW filters are apparently proprietary
designs. I will be especially interested in seeing IMD/BDR
measurements for the variable filters since *variable* also
may imply *variable* IMD/BDR results (depending on BW).
I feel it's still important to see "in radio" IMD/BDR
results before selecting any filters. If the 8-pole 2.8 kHz
should have better results than the stock 5-pole 2.7 kHz, I
hope Elecraft will consider making the 8-pole standard with
for an additional charge of $41 ($120-79) to K3's base price.
IMD/BDR measurements should take most of the mystery out
of the filter choice process for most of us, but IMD measurements
are not totally straight-forward as KC1SX (ARRL), W2VJN (Inrad)
and NC0B (Sherwood) can tell you. Let's QRX and give Elecraft
a chance to do the measurements carefully.
73, Bill W4ZV
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