I have following circuits :
Rf Amplifier :
The amplifier is able to give me a good gain of around 200 to 300 for signals in 100 MHz range. The mixer, which follows the amplifier, is more of a copy paste job to which I have added a couple of resistors to simultaneously amplify the output a couple of times.
The amplifier is preceded by an RF filter. The mixer is followed by an IF filter ( 10.6 to 11 MHz). So the scheme is as follows :
Rf Filter -> Rf Amplifier -> Mixer -> IF Filter
The Rf filter and Amplifier taken together work as expected. The mixer and IF Filter together work as expected. But problem occurs when I connect the Amplifier to the Mixer.
My output suddenly goes pretty weak and low frequencies begin to appear superimposed on the intended 10.7 MHz ( and nearby) frequencies.
Here is the output for 100 MHZ input signal :
while ideally it should have been my intermediate frequency 10.7 MHz.
Can someone tell me where am I going wrong ?