[Elecraft] Improvement changes to K2 and K1 transceivers

[Giancarlo Moda]

Hi Bill and Geoff,

thanks for your comments.

I am sorry I replied through  the elecraft newsgroup.

73

Gian
I7SWX

--- Geoffrey Mackenzie-Kennedy
<gmk at gm4esd.fsworld.co.uk> 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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