- #1
zambadeos
- 3
- 0
Hey!
I've a simple (and maybe stupid) question about the accuracy of an OSA. The datasheet report a level accuracy of 0.4 dB but this seems quite strange to me. Indeed level measurements are done in dBm thus, as long as dB measures a relative power, I assume that even the 0.4 dB are referred to 1 mW as in the case of dBm. Am I correct?
If yes what sounds strange to me is that if I measure a power near to 1 mW than the relative error will be quite high (I'm measuring something like 0 dBm) and as the power that I'm measuring decreases also the relative error decreases.
An example to explain my problem:
1) P=0.4 dBm, the relative error is equal to 100%. Expressed in mW means that I'm measuring a power of 1.096 mW
2) P=-65 dBm (the minimum detectable level for my OSA), the relative error is equal to 0.6%. Expressed in watt: [itex]P= (0.316 \pm 0.002)~nW[/itex], that would mean an accuracy of 2 pW: quite amazing!
So where is the bug in my reasoning?
Thanks to everyone
I've a simple (and maybe stupid) question about the accuracy of an OSA. The datasheet report a level accuracy of 0.4 dB but this seems quite strange to me. Indeed level measurements are done in dBm thus, as long as dB measures a relative power, I assume that even the 0.4 dB are referred to 1 mW as in the case of dBm. Am I correct?
If yes what sounds strange to me is that if I measure a power near to 1 mW than the relative error will be quite high (I'm measuring something like 0 dBm) and as the power that I'm measuring decreases also the relative error decreases.
An example to explain my problem:
1) P=0.4 dBm, the relative error is equal to 100%. Expressed in mW means that I'm measuring a power of 1.096 mW
2) P=-65 dBm (the minimum detectable level for my OSA), the relative error is equal to 0.6%. Expressed in watt: [itex]P= (0.316 \pm 0.002)~nW[/itex], that would mean an accuracy of 2 pW: quite amazing!
So where is the bug in my reasoning?
Thanks to everyone