While staging a new WSPR site I thought to look at the Zachtek's output spectrum with my KiwiSDR and was surprised to see 120 * N Hz sidebands at -115 dBm, only 20 dB below the main carrier. at -95 dBm Battery powering the Zachtek through a linear regulator removed almost all of the sidbands After some experimentation I found that I could get very good spectral purity by feeding the cleanest of my 12V switching power supplies through a linear regulator which included a 2200 uF filter capacitor. Note that in this screenshot the carrier level is much higher at -47 dBm and the strongest sideband is 40 dB lower at -87 dBm. Here is a photo of the system which shows the linear regulator with the 2200 uF capacitor. Even though the 200 mW output of the Zachtek doesn't overload my receiver and the sideband signals will probably not be detected by WSPR receivers near to me, I think it is good practice to minimize the QRM I generate even at 23 dBm tx output power.