Al and All,
I think you are right. I had wrestled with this possibility, and tried to
make a change to the 8 pole at the last minute. But my K3 went out the door
before they could make the switch. Probably a good thing. So far, I can't
detect any detriment. Of course, I can't switch between the two, so it's
hard to tell. If I had made the switch, I'd probably be thinking it was a
good decision as I would feel things were working great. Well, things are
working great anyway! Some folks may be more discerning that I am, but at
this point, in my ignorance perhaps, I'm satisfied!
Dave W7AQK
----- Original Message -----
From: "Alan Bloom" <[EMAIL PROTECTED]>
To: "Bob" <[EMAIL PROTECTED]>
Cc: <elecraft@mailman.qth.net>
Sent: Wednesday, December 05, 2007 10:36 PM
Subject: Re: [Elecraft] Substitution of stock 2.7 for the 2.8 in the K3
I suspect you would be hard-pressed to see any difference at all between
the 5-pole 2.7 kHz filter and 8-pole 2.8 kHz filter in on-the-air
operation.
According to the K3 FAQ, only the first 30 dB or so of stop-band
rejection is important in the roofing filter - the DSP takes care of the
rest. Of course, the 5-pole filter is actually slightly narrower at the
-6 dB attenuation point. Let's say the 8-pole filter is narrower at
attenuations beyond 10 dB. So the only practical advantage it would
have is a few dB better attenuation between the -10 and -30 dB points.
If there were a VERY strong signal in that range (say from +/- 1.5 to
2.0 kHz from center frequency) the 8-pole filter might prevent it
overloading the ADC/DSP system where the 5-pole might not. To make the
more-expensive filter worthwhile, the signal strength would have to be
right in that few-dB range where the 8-pole filter would work and the
5-pole would not. I think that's a rare enough occurance not to be
worth worrying about.
Al N1AL
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