Computing Channel Power with BB60C

[bbowar]

I am computing channel power with a BB60C and comparing to the value Spike gives me for the same instrument settings. I am using algorithm you sent me last summer for the SA44B. Converting dbm readings to Watts for each bin. Summing all the bins in channel bandwidth. Divide this sum by the noise bandwidth which is computed as shown below.
min_bin_sz=rbw/3.2
min_fft=486111.111/min_bin_sz
order=(int)ceil(log2(min_fft))
fft_size=pow2(order)
noise_bw=(rbw*(fft_size))/486111.111
With the SA44 I was getting pretty much identical readings between my calculated channel power and Spike’s. For the BB60C I am seeing a 1.05db difference.

[Andrew]

Hi bbowar,

I apologize, I am currently out of town and cannot verify, but I believe changing the values 486111.111 to 80.0e6 will correct the equation for the BB60C.

Regards,
A.J.

[bbowar]

If I use the 80.0e6 instead of 486111.111, my channel power matches Spike for a CW type signal, but not a 20MHZ White Noise signal. Below are the values from Spike and my computed channel power using both values.
Spike My ChPwr (486) My ChPwr (80.0e6)
CW Signal -51.62 -52.7 -51.6
20MHZ White Noise -51.5 -55.0 -53.9

[bbowar]

I think I figured it out. I noticed the Video Processor units used by Spike was Power and I was using Log in my setup. I changed the Video Processor units in my setup to Power and now the measurements for both CW and 20MHZ noise signal match to within 0.1db.

[Justin Crooks]

Bbowar,

Yes, good catch. For channel power, you definitely want average+power for your video processing.

[Author]

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