Inductor and Transformer - TRANSMISSION LINE TRANSFORMER

Note the misplaced decimal in the example. It should read 28 not 2.8 .

overdrive and over coupling a product detector

As with most things it seems to be more than meets the eye. In searching through datasheets I found a couple of references to signal strength vs LO. It seems there can be to much drive, to little drive, to much signal or to little signal. The circuit response is also affected by coupling components. To test these ideas I did some more spice runs and created over loading and under loading. I will display the results and we can consider them. They all use BAT54 diodes except the last one which uses 1N34A.

Trying a Product Detector in spice

10uh to 50uh 2mv pk-pk RF in .9mv pk-pk AF out not to bad? How to wind a coil with those values.

The calculator said 7 turn primary and 14 turn each secondary. I adjusted the sim to show the values these turns should produce. Time to wind a transformer when I can get in the shop.  You may have found the circuit we needed. I will try and wind one tomorrow.

Product detector using Germanium diodes

product detector

Product detector 1 to 5

Try different turns ratios and drive levels. that amplifying transformer is at work here.

Spice model test germanium

Test of germanium spice model

2SK669 MOSFET amp with fixed bias

My version of Andy's slider. R1 and R2 put the gate at about 9% of Vcc which will turn the MOSFET on as the MOSFET conducts R6 develops a feedback which balances the circuit. With 1mv in I get just under 500mv out. (notice while the waveform is not very distorted the negative peak is larger.

Increasing the input to 10mv overdrives the amp. Increasing the source resistor will tame the beast.
If you use a pot for the source resistor you can adjust the gain. Just something to look at.
The spice model -
2SK669 Amp
A zipped model in case the other link failed you.
2SK669 Amp Zipped

Germanium lib for spice

Germanium.lib