Improvement changes to K2 and K1 transceivers

[I7SWX]

Hi all,

Elecraft has announced their new super transceiver,
the K3. It sounds like being a real super duper for HF
enthusiasts and something that may give some distance
to JA Black boxes…. price permitting.
The K3 is no more a kit for the hungry homebrewers …
maybe an open box for screws drivers … hi
It is possible that many colleagues will put out for
sale their K2 transceivers, maybe at interesting
prices, to purchase the new K3 RTX. These K2 are
already assembled and for those soldering iron drivers
there is not much work to be done to call themselves …
homebrewers.
The K2 is a nice equipment but I believe there is
still space for improvements.
Following a comment I wrote in one message Re:
[Elecraft] here is how to "get a feel" for a roofing
...  regarding possible mods to the K2, I received
several requests asking for information. This gave me
the idea to publish my ideas. Due tpo the fact that
this newsgroup has, at my knowledge, no possibility to
load files, I have uploaded the documentation in the
EMRFD newsgroup "Files", certainly one of the most
suitable for homebrewers and fiddlers.

http://groups.yahoo.com/group/emrfd/

See for file: “I7SWX possible changes to K2 and K1
RTX”. It is possible you need to be a member.

The documentation reports suggested changes:

1)Front-end mixer replacement and roofing filter
addition. These mods have been implemented and tested
by I0CG in his K2.

2)Demodulator replacement. This is a more complex
change versus the front-end one. It is suggested and
not implemented … so volunteers are welcomed to
implement it and apply eventual project adjustments.

In addition, but without any written instruction, a
proposal for K1 changes is added. I may update this
part at a later date (the italian version of document
is ready).
Like for the K2, the two changes are: 1) Front end
replacement, similar to the K2 mod, and 2) Demodulator
replacement.

Due to the fact that in both stages the NE602 is used,
these replacements require additional stages.
Improvement should be substantial.
Changes are still theoretical as none have been
applied to a K1… here there is more bread and butter
for the homebrewers.
Comments and feedbacks are welcomed.

73

Gian
I7SWX


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[Bill Coleman-2]

On May 8, 2007, at 11:11 AM, Giancarlo Moda wrote:

> See for file: “I7SWX possible changes to K2 and K1
> RTX”. It is possible you need to be a member.
>
> The documentation reports suggested changes:
>
> 1)Front-end mixer replacement and roofing filter
> addition. These mods have been implemented and tested
> by I0CG in his K2.

Part of the beauty of the K2 is that it is a very simple radio,  
superbly executed. (To paraphrase a comment K9AY said to me before I  
bought one)

The K2 uses a TUF-1 balanced mixer with close attention to the  
injection levels and impedance matching. You'd be hard-pressed to  
improve the mixer performance for HF.

Since the K2 is single-conversion, the primary crystal filter IS the  
roofing filter. The primary crystal filter is pretty darn good for CW  
or RTTY.

> 2)Demodulator replacement.

What would you do to replace the product detector? Since the dynamic  
range of the signals after the AGC of the IF stage is pretty limited,  
the NE602 is a pretty good choice. It wouldn't be easy to do better,  
especially at the price point for the K2.


Bill Coleman, AA4LR, PP-ASEL        Mail: [hidden email]
Quote: "Not within a thousand years will man ever fly!"
             -- Wilbur Wright, 1901

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[Geoffrey Mackenzie-Kennedy-2]

Bill,

Gian might be suggesting the use of H-mode mixers to replace the TUF-1 mixer
and NE602 product detector, but I have not asked him. The H-mode mixer has a
much higher 3rd Order Intercept than either the TUF-1 or NE602, but I would
have thought that the very good IMD performance of the H-mode mixer would be
wasted in the K2. As I see it the IMD performance of the 2N5109 post mixer
amplifier, variable bandwidth IF filter and MC1350 IF amplifier (and
probably the front end bandpass filters) would become the weak link, and
determine the overall IMD performance of a modified K2.  Also the H-mode
mixer requires a 50% duty cycle squarewave LO injection for best IMD
performance which would require some modification of the K2's LO and BFO
output circuitry, although this modification might not be necessary because
of the poor (by comparison) IMD performance of the weak link mentioned
above.

73,
Geoff
GM4ESD


 On Wednesday, May 09, 2007 at 2:46 AM, Bill Coleman wrote:


On May 8, 2007, at 11:11 AM, Giancarlo Moda wrote:

> See for file: “I7SWX possible changes to K2 and K1
> RTX”. It is possible you need to be a member.
>
> The documentation reports suggested changes:
>
> 1)Front-end mixer replacement and roofing filter
> addition. These mods have been implemented and tested
> by I0CG in his K2.

Part of the beauty of the K2 is that it is a very simple radio,
superbly executed. (To paraphrase a comment K9AY said to me before I
bought one)

The K2 uses a TUF-1 balanced mixer with close attention to the
injection levels and impedance matching. You'd be hard-pressed to
improve the mixer performance for HF.

Since the K2 is single-conversion, the primary crystal filter IS the
roofing filter. The primary crystal filter is pretty darn good for CW
or RTTY.

> 2)Demodulator replacement.

What would you do to replace the product detector? Since the dynamic
range of the signals after the AGC of the IF stage is pretty limited,
the NE602 is a pretty good choice. It wouldn't be easy to do better,
especially at the price point for the K2.



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[I7SWX]

Hi Bill and Geoff,

thanks for your comments.

I am sorry I replied through  the elecraft newsgroup.

73

Gian
I7SWX

--- Geoffrey Mackenzie-Kennedy
<[hidden email]> wrote:

> Bill,
>
> Gian might be suggesting the use of H-mode mixers to
> replace the TUF-1 mixer
> and NE602 product detector, but I have not asked
> him. The H-mode mixer has a
> much higher 3rd Order Intercept than either the
> TUF-1 or NE602, but I would
> have thought that the very good IMD performance of
> the H-mode mixer would be
> wasted in the K2. As I see it the IMD performance of
> the 2N5109 post mixer
> amplifier, variable bandwidth IF filter and MC1350
> IF amplifier (and
> probably the front end bandpass filters) would
> become the weak link, and
> determine the overall IMD performance of a modified
> K2.  Also the H-mode
> mixer requires a 50% duty cycle squarewave LO
> injection for best IMD
> performance which would require some modification of
> the K2's LO and BFO
> output circuitry, although this modification might
> not be necessary because
> of the poor (by comparison) IMD performance of the
> weak link mentioned
> above.
>
> 73,
> Geoff
> GM4ESD
>
>
>  On Wednesday, May 09, 2007 at 2:46 AM, Bill Coleman
> wrote:
>
>
> On May 8, 2007, at 11:11 AM, Giancarlo Moda wrote:
>
> > See for file: “I7SWX possible changes to K2 and K1
> > RTX”. It is possible you need to be a member.
> >
> > The documentation reports suggested changes:
> >
> > 1)Front-end mixer replacement and roofing filter
> > addition. These mods have been implemented and
> tested
> > by I0CG in his K2.
>
> Part of the beauty of the K2 is that it is a very
> simple radio,
> superbly executed. (To paraphrase a comment K9AY
> said to me before I
> bought one)
>
> The K2 uses a TUF-1 balanced mixer with close
> attention to the
> injection levels and impedance matching. You'd be
> hard-pressed to
> improve the mixer performance for HF.
>
> Since the K2 is single-conversion, the primary
> crystal filter IS the
> roofing filter. The primary crystal filter is pretty
> darn good for CW
> or RTTY.
>
> > 2)Demodulator replacement.
>
> What would you do to replace the product detector?
> Since the dynamic
> range of the signals after the AGC of the IF stage
> is pretty limited,
> the NE602 is a pretty good choice. It wouldn't be
> easy to do better,
> especially at the price point for the K2.
>
>
>
>

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[Geoffrey Mackenzie-Kennedy-2]

Hi Gian,

Good to hear from you. My ISP has been QRT since yesterday and has not yet
delivered any other message from you. Will try to contact you off list about
Blue Light LED mixer switrches.

Sorry for using bandwidth.

73,
Geoff
GM4ESD


----- Original Message -----
From: "Giancarlo Moda" <[hidden email]>
To: "Geoffrey Mackenzie-Kennedy" <[hidden email]>; "Bill Coleman"
<[hidden email]>
Cc: "Giancarlo Moda I7SWX" <[hidden email]>; "Elecraft Discussion List"
<[hidden email]>
Sent: Wednesday, May 09, 2007 2:58 PM
Subject: Re: [Elecraft] Improvement changes to K2 and K1 transceivers

> Hi Bill and Geoff,
>
> thanks for your comments.
>
> I am sorry I replied through  the elecraft newsgroup.
>
> 73
>
> Gian
> I7SWX

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