Non-Input-Related Spurs

NI RF Vector Signal Analyzers (NI-RFSA 18.1) Help

Edition Date: June 2018

Part Number: 372058U-01

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Spurious signals that appear when there is no input signal are known as non-input-related spurs. These spurs are combinations of internal signals that mix and result in a signal in the PXIe-5665 IF. A common type of input-related spur is generated by the internal LO signals. If one or more of the following equations is satisfied, a spur of this type may be created:

mfLO1 + nfLO2 + pfLO3 = fIF1

mfLO1 + nfLO2 + pfLO3 = fIF2

mfLO1 + nfLO2 + pfLO3 = fIF3 (PXIe-5603 only)

where   m is an integer

n is an integer

p is an integer

fLO2 is equal to 4 GHz (PXIe-5603 or PXIe-5605 for RF frequencies ≤ 3.6 GHz) or 800 MHz (PXIe-5605 for RF frequencies > 3.6 GHz)

fLO3 is equal to 800 MHz (PXIe-5603 or PXIe-5605 for RF frequencies < 3.6 GHz)

Note Note  For the PXIe-5665 (14 GHz), the 4 GHz LO2 IN front panel connector is connected to the LO2 OUT PXIe-5653, but the connection is not used for RF input frequencies greater than 3.6 GHz. The LO2 connection can still cause spurs in the high band.

Depending on the IF Filter Selection option you choose, fLO1 and fIFx can be calculated as shown in the following tables.

PXIe-5603 and PXIe-5605 (for RF Frequencies ≤ 3.6 GHz)
IF Filter
fIF1 fIF2 fIF3 fLO1 Range
300 kHz 4601.0 MHz 601.0 MHz 199.0 MHz 4,601.0 MHz to 8,201.0 MHz
5 MHz (PXIe-5605 only) 4610.0 MHz 610.0 MHz 190.0 MHz 4,610.0 MHz to 8,210.0 MHz
Through 4612.5 MHz 612.5 MHz 187.5 MHz 4,612.5 MHz to 8,212.5 MHz

PXIe-5605 (for RF Frequencies > 3.6 GHz and ≤ 7.5 GHz)
IF Filter
fIF1 fIF2 fLO1 Range
300 kHz 601.0 MHz 199.0 MHz 4,201.0 MHz to 8,101.0 MHz
5 MHz 610.0 MHz 190.0 MHz 4,210.0 MHz to 8,110.0 MHz
Through 612.5 MHz 187.5 MHz 4,212.5 MHz to 8,112.5 MHz

PXIe-5605 (for RF Frequencies > 7.5 GHz)
IF Filter
fIF1 fIF2 fLO1 Range
300 kHz 601.0 MHz 199.0 MHz 4,050.50 MHz to 7,300.50 MHz
5 MHz 610.0 MHz 190.0 MHz 4,055.00 MHz to 7,305.00 MHz
Through 612.5 MHz 187.5 MHz 4,056.25 MHz to 7,306.25 MHz

LO Leakage to RF and IF

LO leakage is a portion of the LO signal that leaks from the PXIe-5603 or the PXIe-5605 LO IN to the RF IN or IF OUT front panel connectors. LO leakage to the RF IN front panel connector is most often seen at low tuned frequencies. The PXIe-5665 has three LO frequencies: LO1 tunes along with the RF input frequency, LO2 is fixed at 4 GHz, and LO3 is fixed at 800 MHz.

The following LO leakage signal frequencies are related to the frequency of the LO signal:

  • LO3 leakage frequency: 800 MHz
  • LO2 leakage frequency: 4,000 MHz
  • The LO1 frequency can be calculated, as shown in the following table, where Ftune is the tuned frequency of the PXIe-5665 system.
IF Filter
fLO1 Frequency
PXIe-5603 and PXIe-5605 (for Frequencies ≤ 3.6 GHz) PXIe-5605 (for Frequencies > 3.6 GHz and ≤ 7.5 GHz) PXIe-5605 (for Frequencies > 7.5 GHz)
300 kHz Ftune + 4601.0 MHz Ftune + 601.0 MHz (Ftune + 601.0 MHz)/2
5 MHz (PXIe-5605 only) Ftune + 4610.0 MHz Ftune + 610.0 MHz (Ftune + 610.0 MHz)/2
Through Ftune + 4612.5 MHz Ftune + 612.5 MHz (Ftune + 612.5 MHz)/2


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