Keysight PNA Series 50 GHz Noise Figure Serial Number Limitation
When Keysight first launched the N5244A/45A in early 2009, the idea of 50 GHz noise figure measurements was a distant wish. No work was done on a preliminary design to understand how and where the hardware might fit in the instrument. Two years later, in mid-2011, enough work was done on the 50 GHz noise downconverter microcircuit to see where it might mount. At that point, the chassis design drawing was modified to add holes for the future downconverter mounting - the holes shown here by the red dots.
In Feb 2012, we started building all N5244A/45A instruments with this new chassis panel, and we rolled the serial number at this same time to MY/US520xxxxx.
For older serial numbers, we were left with three options: (1) disallow option 029 upgrades, (2) have the service centers drill holes in the chassis, or (3) have the service centers replace the whole chassis panel. Option 2 has a high risk of leaving metal shavings in the instrument, which can lead to short circuits. Option 3 is risky because it involves a complete instrument teardown and rebuild.
In the end, management made the careful decision to choose option 1. If customers need option 029, the division has been very generous with our trade-in programs.
Upgrading to a B model does not change this chassis panel. The B models have the same serial number restriction.