Spurious signals in 5600

[Alann]

Heyy !

I am getting some spurious signals through my RFSA (5661). Even when no RF input is connected. Here is a screen shot of RFSA test panel. The power level of these spurs is much more than mentioned in specs. It causes the data to over-flow outside the vertical range of digitizer.

Pl. comment ....

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[GovBob]

I tried your setup on my system and did not see spikes like that. Do you just have cable hooked up to your RF input port? Is it possible that you are picking up the 10Mhz clock from an external source?

[Alann]

Hey!

Absolutely nothing is connected to 5600 inout and I am using Onboard clock and i have setup my hardware in configuration shown below....

[JMota]

I'm not going to be of much help here as I'm not familiar with RFSA, but I noticed there is a warning in the test panel screenshot and was wondering if that could provide a hint of what might be going on.

[Alann]

Nope that warning is just because vertical range is set to 2 here (by default), the unwanted signal overflows from that range. Here in the test panel i dont have a control of vertical range of the digitizer. If i set vertical range = 10V, then it gives no warning but the problem still remains.

The actual problem is with the down-converter not with the digitizer. I dont understand what is happening and why its happening ???

[Chris_W.]

Hi Alann,

One last thing you could try is to terminate the input and see what the spctrum looks like. I suspect this won't fix it but it's worth a try.

I would then contact an Applications Engineer by going HERE and selecting "Request Support" for further troubleshooting steps.

Chris W

[Alann]

Hey !

I dont understand what you mean by 'terminate the input', when i have fed no input to 5600.

However if i disconnect 5600 and 5142, no such spikes appear when using digitizer only. But the problem persists when i use 5600.

[Chris_W.]

This is a 50 ohm terminator. This ensures that the RF input is not floating which could be suseptible to outside sources of noise. Like I said, this probably won't fix it and I think you should call an Applications Engineer, but it's worth a try. It sounds like something is damaged on the 5600, but you should work with them to troubleshoot further.

Chris W.

[jj2]

Appears to be LO leakage which happens at lower tuned frequencies. Check your driver software version as the later versions should be automatically using larger IF attenuations for low center frequency settings.

Should be able to use larger IF attenuator to reduce the effect of LO leakge  at the expense of noise floor.