[Elecraft] Substitution of stock 2.7 for the 2.8 in the K3

[Dave Yarnes]

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" <n1al at cds1.net>
To: "Bob" <leschyna at gmail.com>
Cc: <elecraft at 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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