[Elecraft] KX1 improvements

[Geoffrey Mackenzie-Kennedy]

----- Original Message ----- 
Karl Larsen <k5di at zianet.com> wrote:

<snip>


>    The TI chip uses 5 volts at 18 mA in a Mixer configuration. I need to 
> study all the information I have now on my computer and then write up an 
> actual proposed receiver mixer for the KX1 that will knock out nearly all 
> third order image signals.

--------------------------------------------------------------------------

In 2005 a simple modification was made to the H-mode mixer using the 
FST3125, as used in the CDG2000 receiver, a mod I have yet to find on any 
website, which involved adding a potentiometer to adjust the switching 
thresholds between the two pairs of FETs. According to one of the designers 
of the receiver this mod raised its IIP3 on 40m to +50dbm (do not know 
offset) for an input noise floor of -130dbm ( do not know the bandwidth), 
thus achieving on 40m a third order dynamic range of  close to120db - not 
phase noise limited. Apparently the IIP3 of the CDG2000's preselector and 
first 9MHz IF filters 'bottom out' at the same point. Can send you details 
off list if of interest.

The four transformer version seems to work best for me using Mini-Circuits 
transformers, although hand wound transformers on binocular cores work well 
also.

73,
Geoff
GM4ESD