dB power y-scales

dB power y-scales

Postby kwxdso » Fri Nov 06, 2015 2:31 pm

Hello
Some power measurements use dB scale calculated using constant impedance, eq. 50 ohms, giving power levels
for example 0dBm equivalent to 1mW, or in dBW reference level of 1 W of power.
Is this kind of dB power measurement possible to add to Multi-instrument please ? Current FFT uses relative scales in
frequency component displays ?
Regards KB
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Re: dB power y-scales

Postby VirtinsTech » Mon Nov 09, 2015 12:53 pm

There are quite a few methods to display power in Multi-Instrument.

1. Method One
Right click anywhere within the spectrum analyzer window and select "Spectrum Analyzer Y Scale". Under Absolute Mode, there is already "dBu" (0dB reference voltage Vr = 0.775 Vrms) which is equivalent to 1 dBm when the load is 600 ohms. (0.775 x 0.775 /600 = 0.001 w). There is also a "dB" with an adjustable 0dB reference voltage Vr. For example, if a load of 50 ohms is assumed (usually used in Radio Frequency), then a Vr = 0.2236 Vrms should be set. Just click "Set Vr" to bring up the [Setting]>[Calibration] dialog box and enter the value 0.2236 Vrms for Vr. After setting this above, the "dB" will represent "dBm with a 50 ohms load".

Refer to Section 3.3.2.10 of the software manual for details.

Probably we can add an "dBm" option (assuming a load of 50 ohms) in the future.

2. Method Two
There is a DDP called "PWR_X". It is defined as [RMS_X] x [RMS_X] / [Load Factor] for the respective channel. The load factor can be set via [Setting]>[Calibration]>"Load Factor for Power Calculation".

3. Method Three
Use UDDP where you can enter mathematical formula together with DDPs to define a variable.
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