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RSA306 CISPR AVG and CISPR QPk detector issues on EMCVu

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yo3fff
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Joined: April 22nd, 2020, 11:58 pm
Country: Romania

RSA306 CISPR AVG and CISPR QPk detector issues on EMCVu

Post by yo3fff » May 9th, 2020, 6:16 am

Hello,

Using the EMCVu software and RS306 for EMC pre-compliance measurement I have an issue with CISPR AVG and CISPR QPk detectors on 22 to 30MHz frequency range.
The measurement setting is as following:
RefLev = 70dBuV (or less)
Ranges and Limits:
1. 0.1 to 30MHz RBW9k
2. 30MHz to 108MHz RBW120k

first measurement is with CISPR AVG detectors and second measurement with CISPR QPk with dwell = 500ms
The noise floor (without EUT switched ON) is linear from 0.1 to 22MHz than drops about 10dB from 22MHz to 30MHz and goes high again till 108MHz.
This behavior it is happened only with CISPR AVG and CISPR QPk detector but not with others (keeping the other settings the same)!
I suspect this is coming from the fact that the noise floor is improving from 22MHz upward but I have no explanation why it is happening only with CISPR AVG and CISPR QPk detectors.
I've used CISPR AVG (logs) with good results (not the above issue)!
By the way, what is the difference between CISPR AVG and CISPR AVG (logs)?
Ca someone please help me fixing this issue.

Thank you.

BR,

Cristian Negru

w2aew
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Re: RSA306 CISPR AVG and CISPR QPk detector issues on EMCVu

Post by w2aew » May 10th, 2020, 6:58 pm

This is normal behavior. The when using the CISPR detectors, the analyzer uses a 5MHz acquisition BW, vs the 40MHz BW used for the non-CISPR detectors. With the narrower acqBW, the instrument optimizes the IF gain/attenuation settings differently, achieving lower DANL in some frequency ranges. Also, please note that in order to get proper response of the CISPR-QPk detector, you will need to leave the dwell on Auto (2s).

yo3fff
Posts: 11
Joined: April 22nd, 2020, 11:58 pm
Country: Romania

Re: RSA306 CISPR AVG and CISPR QPk detector issues on EMCVu

Post by yo3fff » May 10th, 2020, 11:07 pm

Hi w2aew,

I don't understand why only CISPR QPk and CISPR AVG detector behaves like this but not CISPR Pk+ or CISPR AVG (logs).
Could you please explain?
Also attached (AN_2_Broadcast.png) there is a - with the CISPR QPk and CISPR AVG (logs) that shows lower noise floor between 22 and 30MHz which doesn't look professional.

If this is the case (only CISPR QPk and CISPR AVG), how can I aligned the spectrum in 100k - 30MHz range with the CISPR Pk+ for example (see attached ambient.png)?

Thank you.

Cristian
Attachments
ambient.PNG
ambient.PNG (171.14 KiB) Viewed 130 times
AN_2_Broadcast.PNG
AN_2_Broadcast.PNG (151.44 KiB) Viewed 130 times

w2aew
Tektronix Applications
Tektronix Applications
Posts: 137
Joined: December 2nd, 2008, 2:27 pm
Country: United States
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Re: RSA306 CISPR AVG and CISPR QPk detector issues on EMCVu

Post by w2aew » May 11th, 2020, 6:18 am

Without speaking to the system architect, I am fairly certain that this is due to the fact that only the CISPR Avg and CISPR QPk require the 5MHz acquisition BW processing, while the others all use the 40MHz acquisition BW. At the narrower BW, further optimizations are done in the IF stages to give the best combination of noise floor and dynamic range.

yo3fff
Posts: 11
Joined: April 22nd, 2020, 11:58 pm
Country: Romania

Re: RSA306 CISPR AVG and CISPR QPk detector issues on EMCVu

Post by yo3fff » May 11th, 2020, 11:41 pm

Hi w2aew,

I understand the reason for that but looking to my second -, I hope you agree it is looking not good (22 to 30MHz).
From low frequency up to 30MHz RBW is 9kHz so someone would expect a flat noise floor as it is in the first - but no, for some reason the noise floor drops between 22 and 30MHz. After 30MHz RBW is 120kHz and of course the noise floor rising (which is normal).
Could you please provide a solution to flatten the noise between 100k to 30MHz?

Thank you.

BR,

Cristian

w2aew
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Posts: 137
Joined: December 2nd, 2008, 2:27 pm
Country: United States
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Re: RSA306 CISPR AVG and CISPR QPk detector issues on EMCVu

Post by w2aew » May 12th, 2020, 5:56 am

I am sorry, but the optimizations to the IF stages under these conditions is not something that can be bypassed by the user. I agree that the break in the noise floor isn't what you want to see, but Tek optimizes for the best DANL and SFDR results, not the prettiest results. There isn't a workaround when using those particular CISPR detectors.

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