[Elecraft] K3-schematic and 2-pole crystal-filter

[Wes Stewart]

Except the K3 i-f amplifier is fairly low gain, that gets even lower with hardware AGC.  Noise filters are usually used at the end of a high-gain i-f strip.

Wes  N7WS

--- On Mon, 7/1/13, Al Lorona <alorona at sbcglobal.net> wrote:

> From: Al Lorona <alorona at sbcglobal.net>
> Subject: Re: [Elecraft] K3-schematic and 2-pole crystal-filter
> To: "Jerome Sodus" <jsodus at comcast.net>, "elecraft at mailman.qth.net" <elecraft at mailman.qth.net>
> Date: Monday, July 1, 2013, 11:48 AM
> Hi, Jerry,
> 
> That 2-pole filter is probably there to eliminate any
> wideband noise that might be generated in the 1st IF amp.
> It's a good receiver design technique.
> 
> R,
> 
> Al  W6LX
> 
> 
> 
> 
> 
> >________________________________
> > From: Jerome Sodus <jsodus at comcast.net>
> >To: elecraft at mailman.qth.net
> 
> >Sent: Saturday, June 29, 2013 5:35 AM
> >Subject: [Elecraft] K3-schematic and 2-pole
> crystal-filter
> > 
> >
> >Hello,
> >
> >
> >
> >I posted the work below to an eHam forum and one reply
> suggested posting to
> >this site.
> >
> >Thru another reply I have already verified that my
> interpreting of the
> >K3-block-diagram is ok.
> >
> >So, left unanswered is the reason for the 2-pole
> crystal-ladder-filter.
> >
> >
> >
> >Hello,
> >
> >I'm to give a talk to our club next month about
> "roofing-filters".
> >So, during my talk, I intend to show schematics for
> Yaesu's FT-5000 and
> >Elecraft's K3; I choose these two because of their
> pristine locations on
> >Sherwood's table.
> >
> >I'd have no problem explaining the 5000's
> block-diagrams; seems to follow
> >the "expected script".
> >
> >But, with the K3's schematic:
> >
> >a) on its block-diagram (pg. 64), the five
> roofing-filters seem to not be in
> >the expected location of immediately after the
> 1st-mixer.
> >As I see it, the received signal-flow is...from the
> rec'r antenna, thru
> >LC-bandpass-filters, attenuators, +12dB amp, then the
> 1st-mixer, a +17dB
> >amp, the Noise-Blanker, finally the roofing-filters, and
> now an IF-amp, etc,
> >etc. Am I interpreting the block-diagram correctly?
> >
> >b) on both dwg K3-RF-board and dwg KRX3-sub-rec'r,
> between the 1st-IF and
> >the 2nd-mixer, a 2-pole crystal-ladder-filter is
> labelled as having a BW=14
> >KHz. I'm mystified why this part is there, especially
> since any of the
> >preceding crystal-filters would have a significantly
> narrower bandwidth.
> >Hopefully, someone could explain this conundrum. Also, I
> was not able to
> >locate it on the block-diagram.
> >
> >That's about as far as I got trying to piece together an
> understanding of
> >the K3-circuitry for now.
> >Thanks in advance for any replies.
> >
> >73 Jerry KM3K
> >
> >
> >
> >Thanks in advance for any replies.
> >
> >BTW, I'm only just a few hundred dollars short of buying
> the KX3.
> >
> >73 Jerry-KM3K
> >
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