Low signal level in Spectrum option

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STMN
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Low signal level in Spectrum option

Post by STMN » Thu Aug 29, 2019 9:09 am

Hi,
I’ve got a question about the spectrum option. In the attached screenshot you see an 455kHz IF filter measurement on channel A. AWG output is generating a sweep signal 400-500kHz for the filter input. My output signal on channel A is 80mVpp, but in the spectrum view it is shown as a -78dBµ level.
Could you please tell me, why the represented output level is so low? -78dBµ would actually mean 275µVpp.

Many thanks in advance.
STMN
Attachments
455kHz-Filter_04.png

Gerry
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Re: Low signal level in Spectrum option

Post by Gerry » Tue Sep 03, 2019 4:44 pm

Hi STMN,

The answer to your question is because the time domain signal that you are looking at has frequency components spread out across the spectrum (which you can see in the Zoom overview). If you were to add up all of the frequency components, in the correct phase, then they would total to 170mV p-p (which is includes the +ve and -ve peaks).

Regards,

Gerry
Gerry
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STMN
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Re: Low signal level in Spectrum option

Post by STMN » Tue Sep 03, 2019 9:30 pm

Hello Gerry, and thanks for that information.
What would be the correct settings to sweep an 455kHz IF filter? Is it possible to do it in the spectrum mode, or is the X/Y mode more recommended for that purpose?

Best Regards.

STMN

Gerry
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Re: Low signal level in Spectrum option

Post by Gerry » Mon Sep 16, 2019 11:00 am

Hi STMN,

The answer to your question depends upon what you are trying to achieve with your measurement. So, what exactly are you hoping to see from your measurement?

Regards,

Gerry
Gerry
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STMN
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Re: Low signal level in Spectrum option

Post by STMN » Tue Oct 08, 2019 5:05 pm

Hi Gerry,
thanks for that, my intention is to measure the filter curve, and to determine the center frequency of that IF filter. What would you recommend for this case?

Best Regards.

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