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 <jso...@comcast.net> >To: elecraft@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 > >______________________________________________________________ >Elecraft mailing list >Home: http://mailman.qth.net/mailman/listinfo/elecraft >Help: http://mailman.qth.net/mmfaq.htm >Post: mailto:Elecraft@mailman.qth.net > >This list hosted by: http://www.qsl.net >Please help support this email list: http://www.qsl.net/donate.html > > > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
