Spurious signals in PXIe 5641R IF transceiver

Hi all,
I am using the example named 'RFSG Single Tone Generation.vi' to generate a signal from the RF signal generator and give its output to PXIe 5641R IF transceiver. And then using the FPGA example named 'Analog Input' for PXIe 5641R IF transceiver, i tried to view the spectrum of the generated signal. The spectrum shows some spurious signals that disappear with the reduction in signal span. I have tried it with different Signal Span options and the results are shown in the files attached. I am getting these spurious signals even if i don't give any input to the IF transceiver.
Any ideas why is this so?
Thanks
Attachments:
PXI 5652 [Signal Generator].JPG ‏28 KB
PXIe 5641R [IF Transceiver].JPG ‏71 KB

The center frequency of the generated signal was 2MHz and power level was -30dBm.
I have attached another image that shows the results when there is no input connected to AI port of PXIe 5641R. I get this peak of a very high level at the specified AI center frequency.
Attachments:
5641image.JPG ‏128 KB

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The VCOs in the ADCs and the DACs are completely separate on the two devices. Synchronizing the DACs with the ADCs at a local oscillator level is not officially supported. The ADCs and DACs are fed the same sample clock, so you might be able to achieve some level of synchronization. However, sub-sample synchronized VCOs between the DACs and ADCs is not likely. You can look at the clock circuitry diagram in the installed NI IF Tranceivers Help >>Devices>>NI PXIe-5641R>>Clocking page. The NI-5640R software gives you control functionality into the ADC and DAC chips directly when using LabVIEW FPGA to program the device. You could look at the datasheets for the ADCs and DACs to potentially get some ideas for synchronizing the ADCs with the DACs.
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following situation: I am using the PXIe-5641R (in FPGA-mode) in combination with the PXI-5600 downconverter to get a spectrum.
After trying out with different span widths I've experienced strange frequency errors in the range span <10M.
To negotiate errors in my program I've evaluated also the NI example of http://zone.ni.com/devzone/cda/epd/p/id/6196 - unfortunately same error in frequency happens there.
What is meant with frequency error, for example: I have a transceiver which sends FSK with center frequency 443,92MHz. Readings with span-width = 12,5M shows overall good results.
Reading with span width smaller 10M, eg. 3,125MHz, gives unexpected readings.
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Message Edited by Lars.B on 05-20-2009 04:26 AM
Message Edited by Lars.B on 05-20-2009 04:28 AM
Message Edited by Lars.B on 05-20-2009 04:29 AM

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Get NCO Frequency.vi ‏8 KB

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Attachments:
am mod.jpg ‏81 KB

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