Mixer Stability

[muheeb16]

I am reading this paper on a mixer and here it says that a 10-50 ohms resistor must be added (look at the diagram on the left side) to improve stability.How would this improve stability is beyond me.

 

[AMS012]

It is to provide impedance matching for matching the real part of the impedance to the antenna impedance.

 

[RCinFLA]

Not really anything to do with input Z.

Depending on I.F. freq. there may be low frequency components of the mixing product fed back to input. The resistor dampens the possibility of low freq bias shift oscillations that will effect the mixer. The low frequency bias shift may gate the mixer on and off at the low freq oscillation.

I don't like this mixer much. I would prefer to inject a lower level L.O. into the gate.

 

[Terminator3]

I don't like this mixer much. I would prefer to inject a lower level L.O. into the gate.

Why?

About this topic question: https://n5dux.com/ham/files/pdf/Avoiding RF Oscillation.pdf
see constant conductance circle example. Adding resistor of bigger value can help to get out of unstable region.

 

[biff44]

yes what terminator said. these rf transistors often have GOBS of gain at low frequencies, so you need to dampen out that gain in things like bias circuits, which really do not reject 1 MHz signals very well.