We were taken aback by the low signal level compared to the reference antenna, a beverage directed towards North America. Testing on groundwave signals yesterday afternoon was not promising at all. So we thought something was wrong, and tried every possible way to find out what it was. No luck. So this morning we made some more measurements and called the QDFA Helpdesk, aka Dallas Lankford.
Following his advice we connected two preamps with a total of 24 dB to the antenna. The noise floor barely moved. Dallas also informed us that the QDFA doesn't work too well on groundwave signals. Groundwaves is all we got at the moment of writing, but it now appears that the QDFA works as it should. A beacon on 348 to the SE is attenuated some 10 dB more relative to a beacon on 399 to the NW. Groundwave signals to the SE on 657, 1134 and 1449 kHz are much more attenuated than 399 (which is in the desired direction).
So: It works. We will not know how well until we have skywave signals, especially waiting for Longyearbyen 1485 which is in the desired direction.