[Elecraft] Improvement changes to K2 and K1 transceivers

[Geoffrey Mackenzie-Kennedy]

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.