Stepwise IQ rate in NI-5661?

[VEDIS]

Hi all,

In the C/C++ programming reference for NI-5661 I read following text for the method niRFSA_ConfigureIQRate:

"Purpose Configures the rate at which the device samples IQ values. Bandwidth is equal to the coerced iqRate times 0.8."

Does the "coerced iqrate" mean that I can only set the NIRFSA_ATTR_IQ_RATE stepwise instead of to an arbitrary positive integer IQ rate?
If yes,  where can I find a list of the coerced IQ rates?

Cheers, Vedis

[Andy_Hinde]

Hello Vedis,
First let me apologize for the delay in response to your post.
The best way for you to approach this is to determine the bandwidth you need, then divide that number by 0.8. This would be the minimum IQ Rate needed for the specified BW. You may want to add a bit of guardband to the BW you divide by 0.8 too.
In any case, the driver will coerce the value for you, and always coerces upward to ensure whatever rate you input is treated as a minimum rate. It will always be coerced upwards to the next possible rate.

You can always check to see what this rate ends up as by calling NI-RFSA Commit after setting the value, and then reading back the IQ Rate attribute using the Get Attribute routines. The rate is also accessible by inverting the dT output from the Read function.

Regards,
Andy Hinde
National Instruments

[VEDIS]

Hi Andy,

Thank you for your explanation.

With a small programming effort I found following coerced IQ Rate above 2 MHz

2272727.273 Hz,

2500000.0 Hz,

2777777.78 Hz,

3125000.0 Hz,

3571428.571 Hz,

4166666.67 Hz,

5000000 Hz,
6.25MHz,

8333333.3 Hz,

10MHz,

12.5 MHz,

16666666.67 MHz,

25 MHz

Best regards

Vedis