So i am in the early design phase of a new project. Something all secret squirrel that I am working on with a friend. Anyway, so the problem i faced was how to transform impedance from 50 ohms of the antenna, filter etc to the 1500 ohms of the input to a NE602 mixer. There are eleventeen different ways to do this and the way i ended up going about it was to add a low pass filter element after the double tuned bandpass filter I am using.
This has a bit of a bonus effect of also improving the high side slope of the bandpass filters shape. So I fired up RFsim and designed the match, and was confused about the shape of the low pass filter. I am not sure why there is some sort of resonant effect making the frequencies around the cut off go higher than 0dB.
Kind of confused about the simulation RFsim was giving, i fired up LTspice and simulated there, were the resonant effect became apparent, with the 9dB increase in the pass band. I assume that is some kind of artefact in the simulation. I will know soon enough when i build and measure the match.
So then i added in the rest of the filter into LTspice and well I think that should work well enough and is a simple solution that does not require the winding of any transformers. Oh and the reason why I am avoiding transformers, is that this is going to be build all in SMD components and I want to avoid the winding of any inductors at all costs.