Better to use a portion of signal spectrum as reference signal, rather than image shift.

From Alex Pettit, via SARA Mailing List, 5/11/2025:

Andrew, see if this analogy helps :

The Top 3 Data/Drift Pair shows using an image shift to measure system or sky changes. ( aka the 1423 MHz freq shift ‘Dicke-Switch’  technique )

The Bottom 6 Data samples shows that, if the same time duration is used for both Data and Drift frames, twice as much data can be collected in the same time period if a portion of the Image ( Data Freq Spectrum ) is used for calculating corrections 

aka

Alex