Specifications

16
❑ Account for mixer characteristics. See Hint # 6.
❑ Measure the same sideband(s) that will be used in
the application.
❑ For double-sideband measurements, select a LO
frequency close to the RF band of interest.
❑ For single-sideband measurements, select a LO far
from the RF band of interest, if possible.
❑ Choose the LO to suit the mixer.
❑ Filter the LO if necessary to diminish spurious signals
and broadband noise.
❑ Keep the LO outside of the measurement bandwidth
if possible.
❑ Filter the IF if necessary to remove LO harmonics
created inside the mixer.
❑ Filter the RF to prevent unwanted mixing.
❑ Test for DSB error by changing IF.
❑ Experiment with different LOs to get the most
accurate (i.e. lowest) noise figure.
❑ Document a frequency plan to evaluate which of the
above precautions are necessary.
❑ Enter proper measurement correction.
See Hint # 7.
❑ Calibrate regularly.
❑ Keep overall gain below the instrument’s spec.
❑ Filter out-of-band power.
❑ If 2nd stage effect is large, add a low-noise pre-amp
(with proper connectors).
❑ Choose the optimal bandwidth. See Hint # 8.
❑ Select a measurement bandwidth no larger than the
pass band of the DUT.
❑ Account for path losses. See Hint # 9.
❑ Avoid adapters as much as possible.
❑ If used, enter their losses into the instrument.
❑ Account for the temperature of measurement
components. See Hint # 10.
❑ Enter physical temperatures of the noise source and
the components of the measurement setup into the
instrument.
Appendix A:
Checklist
Use this checklist to assist with locating the hint relating to
specific issues or considerations. Reading the 10 Hints
Application Note sequentially is not necessary.
❑ Select the appropriate noise source. See Hint # 1.
❑ Use a low ENR source whenever possible.
❑ Avoid adapters between the noise source and DUT.
❑ Double check manually entered ENR values.
❑ Reduce EMI influence. See Hint # 2.
❑ Use clean, undamaged connectors.
❑ Use threaded connectors.
❑ Use double shielded cables.
❑ Use shielded GPIB cables.
❑ Use a screened room.
❑ Use shielding.
❑ Use an analyzer with minimal electromagnetic
emissions.
❑ Minimize mismatch uncertainties. See Hint # 3.
❑ Use an attenuator or isolator if needed.
❑ Use a pre-amp if needed.
❑ Use averaging to minimize display jitter.
See Hint # 4.
❑ Select enough averages to stabilize the measurement.
❑ Use “trace averaging” first to spot measurement setup
problems soonest.
❑ Look for spikes or even small steps in the display that
indicate RF interference.
❑ If time constrained, use more averaging during
calibration than during DUT measurement.
❑ Avoid non-linearities. See Hint # 5.
❑ Avoid the following:
❑ Circuits with phase lock loops
❑ Circuits that oscillate
❑ Amplifiers or mixers operating near saturation
❑ AGC circuits or limiters
❑ High-gain DUTs without in-line attenuation
❑ Power supply drifts
❑ DUTs or instruments that have not warmed up
❑ Logarithmic amplifiers