11812A attenuator kit - warning

[LarryH]

Agilent and AFMETCAL did not seem too concerned with this issue but I thought I better get a word out in case anyone else runs into this issue.
Our 11812A kit used to calibrate to option 50 specs on 8902A's worked fine for about the first year.  After this, we noticed an error in the 20 dB reading on the 8902A's ( 3 of them!). Further testing revealed the 11812A 20 dB value appeared off from the supplied data.  Compared to the previous data, there was a noticeable shift in the values.  We returned the unit to Agilent for recalibration.  they sent it back with readings that were even FARTHER out.  Our retesting showed this values to be questionable and that the 50 dB reading was raising some doubt also.  Again it was returned to Agilent.  They first told us to EXERCISE it before us!  My obvious question was: "That is obsurd.  It is not a matter of getting a switch to work.  We are relying on the readings to be a very exact value - at what point could we possibly determine was enough exercise?"  they thought about this for a couple days and finally determined it had some bad switches and made us an outregeous quote.
Anyway, that all said, before you determine your 8902A is out of tolerance (and start a HUGE recall!) do one or more of the following:
1) retest the 8902A with the 11812A on just the 10 dB the setting.  Use the 900G10 (10 dB substitution) method utilizing the 10 dB step.  This will give you good comparison of the 10 dB vs. 20 - 50 dB values.
2) test your other 8902A's.  These units are very stable and the odds of TWO 8902A's being out by the same amount are almost impossible.
3) Exercise the 11812A a couple of times and insure the readings are repeatable out to 2-3 digits for all settings
4) I use a 3335A generator as a comparison standard.  The 3335A attenuator use to be THE STANDARD at the Loveland, CO Hewlett-Packard standards lab.  As such, it provides VERY consistant readings year to year.  With a calibrated 8902A and correction factors, I plotted a 3335A out to 3 digits.  It provides these values repeatedly to within a couple digits. aaaaaaaaaaaa