HP 8924C RF Output Discrepancies below 30 MHz                   Amtronix Instruments, Inc.

    Most HP 8924C units have an electronic input module. The electronic input module has electronic switching (vs. mechanical relays) in the output step attenuator to lower the chance of a failure. This also causes the RF output level below 30 MHz to be less than what the display indicates. Because of several variables, the chart could have 2-3 dB of uncertainty and is intended only to help the user be in the "ballpark". The chart below shows how much a typical HP 8924C's output level is attenuated at frequencies below 30 MHz. The chart measures the discrepancy in output level at -121 dBm (0.2 uV) for frequencies below 10 MHz.  The discrepancies increase as much as 5 dB when measured at higher output levels. Discrepancies also vary as much as 1 dB from unit to unit. From 10 to 30 MHz, the error should be below 0.5 dB.

 Frequency             HP 8924C actual RF level output offset from displayed RF level output  at -121 dBm
400 KHz                    -26    dB
600 KHz                    -21    dB
800 KHz                    -19    dB
1.0 MHz                     -16.5 dB
1.9 MHz                    -7.5 dB
2.0 MHz                    -7.0 dB
3.0 MHz                    -3.0   dB
3.8 MHz                    -2.9   dB
4.0 MHz                    -2.7 dB
5.0 MHz                    -2.6 dB
6.0 MHz                    -1.9 dB
7.0 MHz                    -1.1 dB
8.0 MHz                    -0.8 dB
9.0 MHz                    -0.7 dB
10 MHz                    -0.6 dB

Also to be noted is the HP 8924C Spectrum Analyzer level will be low at 6 MHz and below. The factory specification for the 8924C Spectrum Analyzer has a level slop of 2-3 dB. The typical 8924C spectrum analyzer shows levels about 1 dB low. at all frequencies. Technical personal at HP indicated this as normal with the 8924C. Below 6 MHz, whatever error the spectrum analyzer already has at higher frequencies is increased by the amounts indicated below. This information was measured from 2 HP 8924C units and most other should be in this ballpark.

Frequency                Error from displayed level (displayed level will be this amount off from actual signal)
400 KHz                    -10 dB
600 KHz                     -7 dB
800 KHz                    -5.7 dB
1.0 MHz                   -4.7 dB
2.0 MHz                    -2.4 dB
3.0 MHz                    -2.1 dB
4.0 MHz                    -1.5 dB
5.0 MHz                    -1.0 dB
6.0 MHz                    -0.3 dB