Non-contiguous Spans

[Ken W]

I'm learning a lot about RF and the 5660, but I think some pointers could accelerate my learning curve.  I'm trying to use LabWindows 8.0 (based on the sample apps) to detect and measure peak value levels (dBm) on up to 12 different frequencies.  I need to use a bandwidth of 10 kHz and the frequencies may range anywhere from 2 MHz to 500 MHz.  I'll know the freqs in advance, so I don't have to find them (other than there may be some error with independent time standards).   An example frequency set would be: 3.237, 5.745, 12.315, 32.050, 233.900, 262.800, 291.200, 299.500, 308.100, 374.950 (MHz).

My question is if the 5660 can read multiple (up to 12) non-contiguous spans quickly?  Or does that require a slow configuration call in between each span?  My goal is to get the peaks of each frequency aproximately every 250 mSec.

One additional hurdle is that my application needs to change an external RF switch (which determines the source of input to the 5600) in between readings of the frequencies.  This is because my receiver system has multiple antenna's and depending on the frequency the application has to select the right one.  So I may have to read 4 spans, change the RF switch, read 4 more spans, change the RF switch again, and then read the final 4 (of my 12) spans to obtain all 12 frequencies.  Would it be best to handle this by reading my entire range of spans 3 times (finding peaks on just the appropriate freqs each time) or can I quickly reconfigure the 5660 after each RF switch change?

Thanks,
Ken

Message Edited by Ken W on 12-29-2006 03:32 PM

[David S.]

Hi Ken -

Our downconverters only have a 20MHz span.  Because of this, you'll have to retune the VSG to acquire all the tones in your list.  However, the tuning speed is <1ms, so it'll be very fast for your application. 

Unfortunately, to get the very most efficient performance, you'l have to tweak parts of the 5660 "driver" VIs to suit your application specifically.  You can use the ni5660 Configure for Spectrum VI to set up a frequency list.  (If you look inside the VI, you'll see that it builds a list of center frequencies for scanning if you specify a span greater than 20MHz.  You'll want to use this section of code to build your own custom list.)  When you call the ni5660 Read Averaged Power Spectrum VI, it'll take that frequency list and loop through it.  The device is tuned to the next frequency in the list by sending it a software trigger.  (Every time this trigger is received, the device tunes to the next listed frequency.)

I hope this helps.  Let me know if you have any more questions as you dig into the code.

[Andy_Hinde]

Hi Ken,
You could save some tuning time by acquiring some of the lower frequency peaks within a single 20 MHz BW spectrum and doing a multiple peak search on this data. Instead of tuning to these individual peaks you could center the spectrum around the peaks, acquire a large spectrum, and do a peak search measurement that finds all the peaks.

The tuning time of the PXI-5660 RF VSA is about 20-30 ms due to the YIG oscillator in the PXI-5600 RF Downconverter, so each new configuration would take at least this long.

Regards,
Andy Hinde
National Instruments

[David S.]

I stand corrected.