[Elecraft] k3 filters and kx3

[Edward R. Cole]

Although I agree comments from Elecraft engineering would be welcome, 
my understanding is the KX3 has no IF.

The KX3 is direct-conversion from RF to baseband audio.  Therefore, I 
would expect the "roofing" filter to not be working at RF and be 
analog.  A direct-conversion receiver is typically very broadband at 
RF so roofing filters would have to be used at baseband before 
conversion to digital.

The K3 is a dual-conversion SDR so the roofing filters are at 8.215 
MHz (1st IF).  Second IF is 15-KHz which is the baseband.  I expect 
the baseband on the KX3 to be about the same to accommodate 
FM.  Roofing filters inserted at baseband would improve SNR on 
narrower bandwidth modes and maybe help discriminate out of band signals(?).

But I am guessing.
Send me a KX3 and I will look "under the hood" and tell you what I 
see - joking.

I plan to include the roofing filter with my KX3 order.  Just waiting 
to hear the opening bugle!  "the horses are at the starting gate".

73, Ed - KL7UW

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Message: 38
Date: Wed, 14 Dec 2011 08:51:15 -0500
From: "Terry Posey" <tposey at nettally.com>
Subject: Re: [Elecraft] k3 filters and kx3
To: "'Bruce Beford'" <bruce.beford at myfairpoint.net>,
         <elecraft at mailman.qth.net>
Message-ID: <000001ccba67$73463300$59d29900$@com>
Content-Type: text/plain;       charset="us-ascii"

The Elecraft KX3 architects should weigh in on this topic - a simplified
block diagram would be helpful.  The KX3 roofing filter is likely a analogue
filter realized with precision op amps and operating at the KX3
low-frequency IF (11 KHz?) - not "baseband".  The roofing filter is applied
prior to the ADC and DSP, and not at baseband audio frequencies, else it
would not be roofing filter, but merely a post audio filter.

Terry K4RX


No, the KX3 roofing filter module is completely different. It works at
"baseband" frequencies, rather than the 8+ MHz IF that the K3 uses. You will
not be able to use K3 filters in the KX3.

Bruce, N1RX

 > Can the K3 roofing filters be used in KX3 ?





73, Ed - KL7UW, WD2XSH/45
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