03-31-2009 09:21 AM
I'm using a PCI-4474 DAQ card and Labview to create a spectrum analyzer.
I keep getting a -7 dBm result on my FFT graph.
For example if I input a sine wave from a signal generator at 0dBm into the DAQ the result will be -6.98 dBm after going through the FFT.
However if I look at the signal in the time domain in Volts the result is correct. 0dBm = 633mVp-p.
This also occurs if I use a simulated signal VI - I get the same discrepancy in the FFT
Anyone else experiance this or know what I may be doing wrong?
04-01-2009 02:26 PM
Hmmm
0.633Vp-p= @0.208Vrms. Assuming 75Ohms Power = V^2/R = @0.578mW or about -7dBm