Input filter for SA612 mixer

We are planning to build a simple Direct Conversion RX, but with a Si5351 digital sythesiser VFO. The Si5351 has a square wave output with lots of harmonics. In order to limit these and avoid unwanted mixer products a simple filter is to be put infront of the VFO input.


This is simply a 22pF capacitor and a 22uH inductor (commercial resistor-style) loaded by a 51R resistor. The Si5351 happily drives a 51R load with about the right input level for the SA612. The response of this arrangement is,



Which looks good. Now to try it in practice...