NI 5671 IQ Rates

In Arb waveform and Script generation modes the NI 5671 supports several IQ rates:

• 100 MS/s—default. Waveforms sampled at this IQ rate can use the full 20 MHz bandwidth of the NI RF signal generator. No other IQ rate can use the full bandwidth of the NI RF signal generator.
• 50 MS/s — This setting has several specific situations in which it is useful. These situations are discussed in more detail in the following section.
• (100 MS/s)/n, where n = 12,14,16,...,512,516,520,...,1024 (for example, n is divisible by 2 between 12—512, and divisible by 4 between 512—1024). Using one of these IQ rates enables the DUC.

Refer to the IQ Rate (S/s) property or the NIRFSG_ATTR_IQ_RATE attribute for more information about IQ rates.

When to Use a 50 MS/s Rate

The NI 5671 supports 50 MS/s only for compatibility with applications written for the NI 5670. The highest DUC IQ rate is 8.33 MS/s, which supports signal bandwidths up to 6.66 MHz. Sampling at 50 MS/s only supports signal bandwidths up to 5 MHz. Using the NI 5671 with an IQ rate of 50 MS/s will work, but using one of the DUC rates instead requires less AWG memory and generally requires less processing time.

Implications of Using a 50 MS/s Rate

Setting the IQ Rate property or NIRFSG_ATTR_IQ_RATE attribute to 50 MS/s has the following implications:

• NI-RFSG is forced to place the IF carrier frequency at 18 MHz ± 0.5 MHz to avoid aliasing. Forcing the IF carrier frequency to that point implies that NI-RFSG does not have the freedom to pick an IF carrier frequency that could optimize the waveform size if phase continuity is enabled.
• Output signal bandwidth must be less than 5 MHz to avoid aliasing.
• Close-in phase noise is higher.