periodic ripples on the control voltage of oscillator

[chuckey]

the 2 X F on the varactor node is due to the varactors having their bias modulated by the RF. If the RF is + on one drain , it increase the bias, but the resulting -ve on the other drain reduces the bias, so the varactor tap follows the + RF on the one drain. But when the rf goes negative the varactor tap follows the other drain voltage, so in one cycle of RF the varactor bias goes +ve twice. Try more bias, less RF, better varactor fets if you are really worried.
Frank

 

[hanikapa]

Thanks so much