A quick look at the Elecraft filter response plots for the KFL3A-250 and
KFL3A-400 shows these bandwidths:
dB -250 -400
-6 400 420
-20 480 530
-40 600 700
-60 780 920
So, the narrow filter won't make much difference close in, but may
provide more rejection more than 200 Hz from the center frequency.
(Assuming it hasn't drifted too far.) Another way to look at it is that
the narrow filter has about 10 dB more rejection beyond +/-200 Hz.
This, of course, adds to the DSP rejection, and may prevent overloading
of the DSP by a strong adjacent signal. How often this makes any
difference is hard to say.
I can say that I can't recall ever switching to the narrow filter to
reduce QRM from a signal more than about 400 Hz away. I frequently do,
however, for those less than 200 Hz away, in which case the extra
rejection must come almost entirely from the DSP.
Scott K9MA
On 1/1/2018 13:35, [email protected] wrote:
So I guess you're saying that there is not much difference, only 55Hz, so
maybe it is not worth the cost of having both. My K3S's are programmed to
switch these roofing filters in closer to their actual passband. The cost of
the 250Hz filter is a small percentage of the transceiver cost so I do not
mind having this option. I see it being far more useful than the 1.0Khz
filter. WD8Z said that he ordered the 400Hz by mistake and my initial
comment was that it is a fantastic CW/RTTY filter. I have two in each of my
K3S's.
John KK9A
-----Original Message-----
From:[email protected] [mailto:[email protected]]
Sent: Sunday, December 31, 2017 10:58 PM
To:[email protected]
Cc: 'Elecraft Reflector'
Subject: RE: [Elecraft] filters
The actual passband of these two filters is more important than the
marketing name. The "400 Hz" filter is about 435 Hz wide at the -6dB
points. The "250 Hz" filter is about 380 Hz wide. Look at the graphs on
the Elecraft website.
Ed W0YK
--
Scott K9MA
[email protected]
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