Notes for Blocking Dynamic Range
We measure BDR by centering a weak signal (MDS-level) in the passband, and then slowly increasing the power of the out-of-passband strong signal. When the level of the weak signal drops by one dB, we know you've reached the level at which a strong out-of-passband signal will desensitize the receiver. The "range" itself is the difference between the MDS and the power of the strong signal, expressed in dB. The higher the range, the better.
There is interesting issue with BDR. Sometimes, the strong signal will start mixing with phase noise of the local oscillator or synthesizer before any gain compression has occurred. When this happens, the weak signal seems to increase, rather than decrease. The ARRL has coined the phrase "noise limited" for this situation, and we have followed suit. If noise limiting has occurred at a low dynamic range, it is a hint that the receiver has problems with phase noise.
Paradoxically, noise limiting can occasionally mean that the receiver has good phase noise and dynamic range performance, if the limiting occurs at a high dynamic range.
When noise limiting occurs, it means that the test for blocking dynamic range cannot be completed. For this reason, we do not include noise limited test data in our bar chart. Instead, we list the data in a table below the chart.