SA44B noise floor 50 ohm load

Hello,

I just sweep the entire spectrum of SA44B (100kHz to 4.4GHz) with its input closed by a 50ohm dummy load. It looks like there is about +20dB increasing in noise floor from lower to upper frequencies (from about -90dBm to -70dBm). I used 10kHz RBW/VBW. I’ve tried both reference levels 0dBm and -50dBm but got the same result.

In 10kHz BW at 300K room temperature, the thermal noise is -134dB.

Is this a normal behavior because I just got the SA44B as a brand new.

Thank you.

BR,

Cristian

[Andrew]

Hi Cristian,

If I understand your question correctly, then yes, this is normal behavior. I will include two images of the setups of my working SA44B so you can compare.

I will sweep from 100k – 4.4Gz with 10k RBW at both reference level of 0 and again at -50.

Your results may not match exactly, but should be close.

Regards,
A.J.

• This reply was modified 8 years, 8 months ago by Andrew.

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Hi Andrew,

Thank you for the answer. My SA44B look almost the same. I don’t understand what are those spurs around 500-800MHz?!
Do you have in your future plans to normalize the overall noise floor?
Like measure it then mathematically extract it from the measurements the display it just to look linear.

In a 100kHz-100MHz span with RBW/VBW 6.5kHz and -60dBm ref. the noise floor was about -115dBm average. For this BW the thermal noise at 300K is -136dBm. That means that the overall analyzer’s noise contribution is 21dB?

Thank you.

BR,

Cristian

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Hi Cristian,

The spurs between 500-800 MHz are from internal clocking mechanisms.

There are no plans to ‘flatten’ the noise floor. This would require new hardware development.

As for your last questions, I didn’t verify the values, but assuming the numbers are correct, the answer is yes. This can be considered the analyzers noise contribution, also referred to as noise figure.

Regards,
A.J.

[Author]

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