memory limit 5660

[rajeshj]

I want to acquire a signal of 160 MHZ using 5660. Can I set the sampling frequency to be 350 MHz? I want to acuquire the signal for 5s. How much memory is required to acquire the signal? Will there is any limitation in memory usage?

Regards,

Rajesh.

[JKnMI]

Rajesh,

You can definitely acquire and analyze a 160MHz signal (up to 2.7 GHZ), but your sample rate is always 64MS/s. This is possible because the PXI-5660 is made up of two two PXI modules, the PXI-5600 RF downconverter, and the PXI-5620 frequency domain digitizer. The PXI-5600 performs a down conversion of the 160MHz signal to a lower freqency before it is read by the PXI-5620 digitizer and analyzed using the spectral measurments toolkit (SMT). If you sample for 5 seconds reading samples of type double (8 bytes), you will be reading 64 MS/s X 8 Bytes/sample = 512 MB/sec per channel. For one channel, 5 seconds of data will be 2.56 GB. If you use a simpler data type this number will be less, if you use a larger (i.e. waveform type), this number will be greater. You can learn more by reading the The NI PXI-5660 RF Signal Analyzer Extends Virtual Instrumentation into GHz Applications tutorial.

Regards,

Jessica
Applications Engineering

Message Edited by JKnMI on 09-30-2005 12:24 PM

[Andy_Hinde]

Hello Rajesh,
A 5 second acquisition at 64 MS/sec equates to 320 MSamples, which at 2 bytes per sample (the 5620 is a 14 bit digitizer) would require 640 MB of onboard memory, far greater than the 64 MB maximum offered. However, if you are acquiring a narrowband signal that is <= 1.25 MHz the onboard Digital Downconverter (DDC) will turn on on the 5620 digitizer, which reduces the data rate.  However, when the DDC is on, each complex IQ sample is composed 4 bytes. At 1.25 MHz, the sample rate becomes 2 MS/sec, which at 4 bytes per sample and 5 seconds comes to an onboardd memory requirement of 40 MB, which is possible with a 64 MB 5620. Smaller bandwidths reduce the sample rate even further, so if your acquisition bandwidth is <= 1.25 MHz, then a 64 MB 5620 will do the trick.

Regards,
Andy Hinde
National Instruments