Is there a method to improve measurement data correlation between the 8970B and the N897xA Series Noise Figure Analyzers (NFA)?

For data correlation issues, one of the factors to consider is frequency accuracy. The frequency accuracy of the N897xA is equivalent to ±(reference error + 100 kHz). However, the frequency accuracy of the 8970B is ±(1 MHz + 1% of frequency to a maximum of ±6 MHz). If the device under test (DUT) is sensitive to input frequency, this could cause a significant difference in the DUT test results for both noise figure and gain.

If you suspect frequency sensitivity is the cause of non-correlated data, perform the following to determine the tuned frequency accuracy of the 8970B. The test is accomplished by using a high performance signal generator. A frequency counter may be of assistance in confirming the source´s output frequency.

The example below provides an 8970B accuracy check at 1 GHz. Based on the specifications, the 8970B can vary by (1 MHz + 1% * 1 GHz) = 1 MHz + 10 MHz = ±11 MHz. However, the maximum error is specified as ± 6 MHz. Therefore the error for this configuration could be 1 GHz - 6 MHz to 1 GHz + 6 MHz, or 1.006 GHz to 0.994 GHz.

Connect the output of the signal generator to the input of the 8970B.
Preset the 8970B via "0.9 SP (Special Function)"

Set the START and STOP frequency of the 8970B to 1 GHz.

Set the frequency of the signal generator to 1 GHz and the output mode to CW.

Set the output level of the signal generator to -90 dBm.

It is recommended that the signal generator´s frequency and power levels be confirmed via a counter, power meter, or spectrum analyzer.

Press "9.1 SP" in the 8970B. This is the direct power measurement mode. The displayed power on the 8970B is the relative power above -174 dBm/Hz. For this configuration the analyzer displayed approximately 18.5 dB. Given that the 8970B samples in a 4 MHz bandwidth the expected measurement, over -174 dBm/Hz can be calculated as
Expected Level = -174 dBm/Hz + 10*Log10(4 MHz) - Signal Generator output level
Expected Level = -174 dBm/Hz + 10*Log10(4E6 Hz) - (-90 dBm)
Expected Level = -174 dBm/Hz + -66.0 - (-90)
Expected Level = 17.9 dB (for special function 9.1, power measurement mode)

Change the frequency of the signal generator until the level displayed at the 8970B is maximized.
Increase the frequency of the signal generator and find the -3 dB point from the peak level.
Record the frequency of the signal generator: F1
Decrease the frequency of the signal generator and find the -3 dB point from the peak level.
Record the frequency of the signal generator: F2
Calculate the actual tuned frequency of the 8970B: Factual = (F1 + F2)/ 2
This frequency error may be the source of correlation issues.