Test Setup using High Precision 50 ohm Load
The scan in Figure 1 show the results using an AIM 4170UHF network analyzer utilizing a high precision 50 Ohm load.
Test setup utilizing a 50 ohm non inductive resistor w/ wire leads
This is the same scan with the only difference being the 50 ohm load that now has wire leads. Note the dramatic impact of stray capacitance picked up by the leads of the resistor.
For those interested, here is the full layout of the test setup using the AIM 4170. We should also note the impact of this capacitance is the most noticeable on 1:1 baluns. The complex winding of other ratios tends to dampen or eliminate the effect of this capacitance on test results.