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[SOLVED] Mosfet mixer gain problem

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gpugelni

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I have problem with this mixer on picture. Is it normal that after BF981 IF amplitude is lower then input signal in mixer (70MHz)? Would not this kind of mixer have some small gain? For XTAL I use 20MHz crystal instead of 60MHz (because I can't find 60MHz crstal) , I have oscilation of 60 MHz on G2, but I'm not sure is it ok to use 20MHz instead of 60MHz.. Also I have mixed IF of 10 MHz on output, but it's amplitude is to small. Input singnal is 5dBm and out put is still small...

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Regards,
 

Its ok to use a 20MHz crystal, but have to use a different topology for your Colpitts oscillator.
Use at the collector of the oscillator an LC circuit tuned at 60MHz (3rd harmonic), and pick the LO signal inductive coupled to the collector inductor.
The 20MHz crystal goes to the ground using a trim capacitor, or even an inductor if want to decrease just a little bit the oscillator frequency.
 

I was find out what is the problem, replace BF981 with BF960 and you will get 20 dB of gain.

Regards,
 

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