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K3-schematic and 2-pole crystal-filter

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KM3K

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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alorona

Re: K3-schematic and 2-pole crystal-filter

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 <[hidden email]>
>To: [hidden email]
>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:[hidden email]
>
>This list hosted by: http://www.qsl.net
>Please help support this email list: http://www.qsl.net/donate.html
>
>
>

______________________________________________________________
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Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[hidden email]

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n7ws

Re: K3-schematic and 2-pole crystal-filter

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 <[hidden email]> wrote:

> From: Al Lorona <[hidden email]>
> Subject: Re: [Elecraft] K3-schematic and 2-pole crystal-filter
> To: "Jerome Sodus" <[hidden email]>, "[hidden email]" <[hidden email]>
> 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 <[hidden email]>
> >To: [hidden email]
>
> >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:[hidden email]
> >
> >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:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>