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Re: Modifying Bitx40 BPF band pass filter

 

The diode ring mixer needs more than 0.6 V so as the diodes will conduct.
Positive and negative cycles of oscillator will make one pare of the diodes
switch on and conduct in one and then other pair. and allow the RF from
the mixer to go to the IF and so on.
You are giving only 0.2 V to the diode mixer so it is not working and you are?
not getting any thing.
The buffer amplifier comes in to picture here witch boosts the VFO to the?
required 0.6 V

On Wed, Mar 7, 2018 at 8:47 AM, <kaapstad1@...> wrote:

Thank for your input Jerry. I may not have explained it very well. Yes, the ring mixer is lossy and the 200 mV sine coming from the AD9850 is pretty low at those higher frequencies. That is why, in the design I use, the ring mixer module has an extra 2N3904 buffer/amp stage which is not in Farhan's original design. Take a look at this schematic if you will. The 2N3904 seems to be used as a buffer stage before it enters the ring mixer. Maybe the signal is not amplified at all, only buffered. My knowledge is too limited. If so: it there an easy way to modify the circuit so it amplifies it a bit?
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