[Lowfer] Upconverter designs.

[Ben Hall]

Good morning all,

A few weeks ago I purchased a 3.000 MHz OCXO on the e-place.  Per my 
signal counter (calibrated against a 10 MHz GPS DO) it is dead nuts on 3 
MHz, plus or minus half a Hertz.  ;)

Looking at the April 2002 QST article "AMRAD Low Frequency Upconverter", 
there is the following:

"The other approach we considered uses a high-speed CMOS Switch, such as 
the excellent design by Johan, SM6LKM.  Johan found that by paralleling 
the CMOS switch sections on an inexpensive and readily available IC, the 
overall loss could be reduced."

The SoftRock series of I-Q receivers use the FST3253 mux/de-mux switch, 
which have an on-resistance that's about 1/10th of the 74HC4053 used in 
Johan's design.  (The datasheet for the 4053 lists a typical 
on-resistance of 70 ohms or so, the FST3253 datasheet lists a typical 
on-resistance of 4 to 7 ohms or so.)

Being that I'm going to layout a custom PCB for my upconverter 
anyways...I'm thinking the FST3253 is the better choice.

Any reason to go with the 4053 over the FST3253?

I'm also toying with the idea of instead of designing an up-converter to 
feed my KX3...to instead design/build an "LF-softrock" to feed the 
sound-card directly.  I'm pretty convinced that the drift seen in my 
captures is due to drift in the KX3.  If I eliminate the KX3...and the 
receiver is driven by the 3 MHz OCXO...that might just eliminate all the 
drift I've got in my receive chain.

thanks much and 73,
ben, kd5byb