118 Chapter 3
PSA Functional Tests
Second Harmonic Distortion (SHD)
PSA Functional Tests
Second Harmonic Distortion (SHD)Test Limits
Test Description
This test checks the second harmonic distortion of the spectrum analyzer by tuning to
twice the input frequency and examining the level of the distortion product. A low pass
filter is inserted between the source and the spectrum analyzer to prevent the second
harmonic from artificially raising the second harmonic product displayed on the analyzer.
The power level at the input mixer is 20 dB higher than specified to allow the distortion
product to be seen. For example, the instrument specification may state that with a
–40 dBm signal at the input mixer, the distortion product should be suppressed by
>–75 dBc.
The equivalent Second Harmonic Intercept (SHI) is 35 dBm (–40 dBm + 75 dBc). This test
is performed with –20 dBm at the mixer and verifies the distortion product is suppressed
by –55 dBc. This ensures the SHI is also 35 dBm (–20 dBm + 55 dBc).
Applied
Frequency Mixer
Level Distortion
40 MHz –20 dBm < –55 dBc
Item Critical Specifications
(for this test) Recommended
Agilent Model
Adapter Type-N(m) to BNC(f) 1250-1476
Adapter BNC(m) to SMA(f) 1250-1700
Cable APC 3.5 mm, 1 meter 8120-4921
Cable BNC, 120 cm 10503A
Filter, 50 MHz Low
Pass Cutoff Frequency: 50 MHz
Rejection at 65 MHz: > 40 dB
Rejection at 75 MHz: > 60 dB
0955-0306
Synthesized Sweeper Frequency: 50 MHz
Spectral Purity: Better than –30 dBc 83630B