I have been asked by private message what it is about the QST Review test methodology that I found invalid. I constructed this explanation of their test in response and I would like to share it with the group.
The testers used a setup that is used by the ARRL Lab to test the loss of Antenna Tuners. When testing an Antenna Tuner the tuner itself converts whatever load is presented by the "Load Box" back to 50 ohms as a termination for the RF Source. The inline HP RF Power Meter is working in its natural 50 ohm domain and should be accurate within the specification of the meter.
When testing a 49:1 transformer however, there is no way to adjust the termination to 50 ohms. So, with an 800 ohm load selected in the load box as the authors specify in the email trail, the RF Source and the source power meter are operating in a 16 ohm environment. What the actual power out of the source is, and what power is indicated on the source power meter with a 16 ohm load, are determined by the characteristics of each box. It most certainly cannot be assumed to be 10 watts. The error in this step can easily be over 6 dB.
When the test therefore shows the transformer to have a loss of 0.2 dB, the actual loss could be as much as 6.2 dB.
The two transformer back to back test that I have documented does not suffer from a load mis-match and is therefore a far more appropriate way to do this measurement.
