[Difx-users] zoom/recband and ACCOR for DiFX 2.6.1

[Jan Wagner]

Noted one strange issue in DiFX 2.6.1. Has anyone noticed this and
can confirm it?

The scaling of DiFX data converted with difx2fits and loaded into
AIPS appears to be different when using zoom band correlation,
versus correlating natively recorded bands:


Case: Stations recoded 32 MHz LSB at 86348.00 MHz. Two correlation
runs with DiFX 2.6.1.

Correlation (1): 32 MHz LSB recorded bands flipped to USB via
addZoomFreq freq at 86348.00/bw at 32.0/noparent at true

Correlation (2): 32 MHz LSB recorded bands correlated as-is


Processing: difx2fits, AIPS FITLD digicor=1, ACCOR solint=2/60,
CLCAL #2 = CL#1 + SN#Accor, POSSM cross power spectra docalib=1
gainuse=CL#2.


Result: compared "flux density" on three baselines and 4 IFs

Data from zoom correlation (1): amplitudes ~0.5 Jy, accor gains
~0.65 or thereabouts

Data from rec band correlation (2): amplitudes ~1.0 Jy, accor gains
~1.00


It is strange that 32 MHz zoom (identical to 32 MHz recoderd except
for sideband flip to USB) would produce a factor 2 difference in the
scaling of cross power spectra. Has anyone noticed this? Is there a
workaround? The experiments in question were already correlated some
months ago and not all raw data are available anymore. In case
someone has already ran into this issue, is simply a "manual"
rescaling by factor 2 in AIPS a permissible solution?

regards,
Jan