Friday, August 12, 2016

playing with the balanced mixer again. The Gilbert cell actually.

A slick little circuit made with 6 transistors, 2 resistors, and a transformer. It is available as an IC but what's the fun in buying a chip when you can build your own? Don't laugh at my breadboard, I made it too. Here's the chip version.

If you could find them it would probably be better than my home built but it's only 6 transistor so here we go.
Same circuit but the IO ports are labeled.
Not much to look at. All the jumpers cover it up. Let's see what it does.  With some signals applied. I don't have a lab but I have a little digital function generator and a grid dip meter. I put the function generator on the LO input and coupled the dip meter to the IF.

You can see the signals are interacting.
I changed the signal a little and it look good considering I don't have lab grade equipment here.
I turned on the frequency display The purple spikes are the input signals. One is dead center, the other to the right. Nice envelope being produced.
This looks much the same but note I have lowered the signal. The spike is to the left now.
My scope is not the best I can only step through the adjustment but here you are seeing the same signal as before but the time base is changed. Note the frequency reading is the difference.
Here I really made some changes to the display same inputs.

Cleaning up a little here.

I pulled the clip leads away and this is the circuit. The round red thing is the transformer I had on the negative supply lead. The junction between the two resistors are the positive supply point. That's it 6 transistor, 2 resistor, and 1 transformer = Gilbert cell.
My project at this time is an 80 meter receiver I might build that circuit into it?

I made a couple of long tailed amps using 2SK2539s and they worked quite well. Now I'm looking at a Gilbert's cell using the JFETs.

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