Here my results: After switch on the LNB-frequency drifts more than 10 kHz upwards. After ca. 45 minutes the frequency is "stable" between +- 1.8 kHz. I transmitted a CW-signal on 437.070.00 MHz and received the 24th harmonic on 10489.675 (middle of NB) --> AMSAT-DL-RXconverter --> Kenwood TS-711E on 144.470 MHz (+-). I heard no wobbling, see the pic:
What do you think, have I found my unmodified LNB ?