HP ESA-L1500A, User'S And Calibration Manual

Page: 253 / 326

252 Chapter 9
Performance Verification Tests
14. Spurious Responses
14. Spurious Responses
This test is performed in two parts. Part 1 measures second harmonic
distortion; Part 2 measures third order intermodulation distortion.
To test second harmonic distortion, a 50 MHz low pass filter is used to
filter the source output, ensuring that harmonics read by the spectrum
analyzer are internally generated and not coming from the source. To
measure the distortion products, the power at the mixer is set 25 dB
higher than specified. New test limits have been developed based on
this higher power.
With
−
40 dBm at the input mixer and the distortion products
suppressed by 75 dBc, the equivalent Second Harmonic Intercept (SHI)
is +35 dBm (
−
40 dBm + 75 dBc). Therefore, with
−
20 dBm at the mixer,
and the distortion products suppressed by 55 dBc, the equivalent SHI is
also +35 dBm (
−
20 dBm + 55 dBc).
For third order intermodulation distortion, two signals are combined in
a directional bridge (for isolation) and are applied to the spectrum
analyzer input. The power level of the two signals is several dB higher
than specified, so the distortion products will be suppressed less than
the amount specified. In this manner, the equivalent third order
intercept (TOI) is measured.
With two
−
30 dBm signals at the input mixer and the distortion
products suppressed by 74 dBc, the equivalent TOI is +7 dBm
(
−
30 dBm + 74 dBc/2). However, if two
−
22 dBm signals are present at
the input mixer and the distortion products are suppressed by 58 dBc,
the equivalent TOI is also +7 dBm (
−
22 dBm + 58 dBc/2).
Performing the test with a higher power level maintains the
measurement integrity while reducing both test time and the
dependency upon the source’s noise sidebands (phase noise)
performance. This test therefore measures the equivalent TOI.
There are no related adjustment procedures for this performance test.
Equipment Required
Synthesized signal generator
Synthesized sweeper
Measuring receiver (used as a power meter)
Power sensor, 100 kHz to 1500 MHz
50 MHz low pass filter
1 GHz low pass filter
6 GHz Directional bridge