AIM 915a produces internally inconsistent results



AIM915 was recently pulled from the distribution site and replaced by a new release, AIM915a.

I cannot recall ever finding a new release that did not have significant defects, commonly inconsistency between displayed values. In the common theme of one step forward, two steps backwards, this version has defects that were not present in AIM910B.

This problem existed in AIM915, it persists in AIM915a.

Let’s review the internal consistency of this part of the display screen.

Most of the values given above are calculated from a single measurement value, and should be internally consistent. That measurement value is translated to different quantities, many based on the stated Zref (50Ω in this case).

Let’s assume that the values given for Rs and Xs are the basis for the other quantities, and check the consistency of those other values with Rs, Xs based on Zref=50Ω as shown.

Above are various values calculated from Rs=49.719Ω, Xs=0.090Ω and Zref=50+j0Ω.

Working down from the top of the AIM results:

  • SWR (1.508) is wrong, it should be 1.01;
  • Rho Mag (0.2027) is wrong, it should be 0.002959;
  • s11 (-0.0028+j0.0009) is ok;
  • % refl power (4.1) is wrong, it should be 0.00087;
  • Return Loss (13.86dB) is wrong, it should be 50.58dB; and
  • Cable Loss (6.93dB) is wrong, it should be 25.29dB.

Does not inspire a lot of confidence, does it?