The test file had two Ku-band tunings (12.6/15.8 and 14.2/17.4 GHz),
which followed X-band.
A) Zero-mean PDif values are seen in ea27, on all IFs.
B) Unsteady PDif values -- suggesting an origin in the band switches
-- were seen on:
ea07A and C, ea13A, ea20C and D (very bad!), and ea25C.