Polyakov mixer using cores, how does it work?
I would like to know how does it work?
In a typical diode polyakof mixer, the LO "opens" one of the diodes on the positive peak, and it opens the other diode on the negative peak. So that RF signal from the antenna is getting sampled and mixed twice each cycle of the LO. The resulting complex waveform has sum and difference frequencies of RF+2LO and RF-2LO, instead of a typical mixer that has RF+LO and RF-LO.
But my question is, how does it work with the cores? In other words, where are the "diodes" formed with the cores?
And why it coud not be done with a single core (not half the frequency then)?
There's no "diode", the two cores are forming a transductor (modulated inductance). You can imagine it as a switch operating at double LO frequency.
A single core could do the same, but couples a large LO voltage into the receiver input.
All right, that explains why the oposite polarization of the cores does not play a role to the circuit.
In the article he explains that the On/Off (varying inductance) of the cores, even if they are completelty switched, has at best case about 9db difference and that explains the large conversion loss.
I was wondering, if I can achieve larger difference between the On/Off states, even if not using square loop cores but just ordinary, will that do?
After all, as far as I understand it, it is the varying inductance that plays role, not if the cores are square loop.
Is that right?
Yes. The transductor effect relies on the saturation charcteristic, not the hysteresis of the magnetic memory core. I'm not sure if a different core gives better performance. I believe the memory cores have been choosen due to there small size.
Generally, it looks to me more as a proof of concept than a good design idea.
Indeed, just a proof of concept. Once I've made this working http://qrp.gr/corerx/index.htm but it was veeery insensitive.
It was very useful to know that a single core could achieve the same switching evvect, with increased feeedthrough from primary to secondary though. Thanks for that.
In some experiments I did, using different non-square loop cores, I have achieved greater amounts of variable inductance. I do not think these cores have never been saturated though, because they were much larger. I measured the max and min with the scope as Vpp. Then converted that to mW. Then calculated the difference in dB.