Spectrum Analyzer unit

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ncc201
Posts: 1
Joined: Thu Sep 03, 2020 9:27 pm

Spectrum Analyzer unit

Post by ncc201 » Thu Sep 03, 2020 9:34 pm

Hi,

I'm using the spectrum analyzer built-in app with Red Pitaya and I'm trying to understand the unit of the y axis. It says "amplitude [dBm]", I'm assuming that means the power in dBm (1 mW corresponds to 0 dBm). I'm hopping to convert this into voltage, and from the spec, it seems like the input impedance is 1MOhm. I tested it with a function generator generating a definite peak-to-peak sinusoidal wave (double check with another oscilloscope), but the numbers won't add up, i.e. the power calculated from dBm doesn't correspond to V_{rms or peak-to-peak}^2/1 MOhm. I also noticed that from the 'setting' in the spectrum analyzer app, one can choose 'dBm' or 'dBu' and even the input impedance. I'm confused. Can anyone help me with this? thank!

Allen

CScotty
Posts: 2
Joined: Tue Sep 15, 2020 7:49 am

Re: Spectrum Analyzer unit

Post by CScotty » Tue Sep 15, 2020 7:58 am

I think you will find the a 600 ohm resistance should be used based on the definition of dBm.

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redpitaya
Site Admin
Posts: 387
Joined: Wed Mar 26, 2014 7:04 pm

Re: Spectrum Analyzer unit

Post by redpitaya » Wed Sep 23, 2020 8:37 am

It is expected to have LV setting and 50 Ohm in both cases and for dBu you can adjust / change load resistance.

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