I was now in a position to calibrate some additional points on the Power meter having completed the calibration of the 11MHz sine wave generator to the -10dBm reference point.
On hand I have the following attenuators which were purchased new from a commercial source. These attenuators do not have a specified tolerance, however they are marked to be used upto 1GHz. For this purpose I assume they are accurate and will form the baseline for calibrating the system. The attenuator values are:
3dB, 6dB, 10dB, 20dB,
The attenuators now allowed me to derive the slope in mV/dB at each measurement point. This was an encouraging result shown in the following table.
Pad(dB) dBm DVM(mV) mV/dB
0 -10 1565 ----
3 -13 1507 19.33
6 -16 1449 19.33
10 -20 1367 19.80
20 -30 1166 19.95
30 -40 958 20.23
39 -49 775 20.26
This shows a slope variation over the measured range of 20.26-19.33 = 0.93mV which equates to 0.93/20 = 0.05dB. Not sure this is a meaningful calculation?
Looking at it a different way. Midpoint over the range -10dBm to -49dBm
= (20.26-19.33)/2 + 19.33 = 19.80
Thus at the bottom of the range @ -49dBm and using 19.8 we derive (1565-775)/19.8 = 39.9dB
ie. at the reference point of -49.9dBm the power meter shows an error of 0.9dB. Acceptable?
Herewith Lab notes showing the calculations.