Total posts : 45366
How do you know the resistors will work if you increase them to 100 k which implies that the 47k won’t? Since you don’t know, as neither do I, the input and output impedances in his system it appears that we both are making educated guesses and I suppose we can honestly differ in our opinions.
My advice is to try it. Adjust from there if it doesn’t work. The 47 k resistors, if they work, will result in less attenuation than the higher resistance components.
True, the loss in signal will have to be recovered with the transmitter gain. This may or may not work but it is worth a try. By the way, this resistor mixer is very similar to that used in the SSTRAN AM transmitter where it works just fine.
Regarding the single supply op-amps, I assume, perhaps incorrectly, that your are thinking of the Norton amps which I have found can cause problems unless the audio signal is properly DC biased which really complicates the design. Perhaps that is a topic for another time.