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Gain Measurements

1st Attempt


The signal generator is connected to the input of the electronics box and the output is connected to the HP spectrum analyser. The output of the signal generator is varied between -85 and -3dBm at 6.426GHz and the amplitude of the resulting peak at 26MHz on the spectrum analyser is recorded. The output power is plotted against the input power and the final result is obtained by extrapolating the line to 0dBm. Measurements made near compression or the noise background are rejected if their chi-squared is greater than nine. The result is then recalculated and the selection repeated. The rejected measurements are shown in red.

It was discovered the day after that the signal generator output was offset below the displayed value. This was measured to be 18.3+/-0.4dB (YoungIm).



Bpm Gain/dB Error/dB
QM14FFx 24.6 0.3
QM14FFy 27.2 0.3
QM12FFx 26.5 0.4
QM12FFy 28.1 0.3
QM11FFx 27.8 0.3
QM11FFy 26.6 0.3
QF9BFFx 27.2 0.3
QF9BFFy 26.0 0.3
QD8FFx 26.9 0.3
QD8FFy 26.8 0.3
QF7FFx 26.2 0.3
QF7FFy 25.9 0.3
SF5FFx 25.5 0.3
SF5FFy 27.7 0.3

2nd Attempt


This time, the signal generator is a Hittite HMC-T2000. It's output range at 6.426GHz is -15dBm to +10dBm. To extend it's range, four attenuators are added and removed in turn between measurements. The output was measured using a spectrum analyser. The loss in the output cable was later measured using a power meter. The effect of the attenuators seemed to vary which caused the gradient of the fitted line to deviate from 1. Therefore, the data are split according to the number of attenuators and analysed separately. The average results is used for the gain.



Bpm Gain/dB Error/dB
QM14FFx 22.1 1.4
QM14FFy 28.0 1.3
QM12FFx 24.6 1.1
QM12FFy 27.0 1.1
QM11FFx 31.8 1.1
QM11FFy 30.7 1.2

3rd Attempt


This is similar to the second attempt except a variable attenuator with a range of 0-70dB is used in place of two of the fixed attenuators. The output power is varied by changing the attenuation and again, the output is measured with a spectrum analyser and the output cable loss, with a power meter. The analysis procedure is the same as in the first attempt.



Bpm Gain/dB Error/dB
QM14FFx 24.4 0.2
QM14FFy 21.6 0.3
QM12FFx 24.0 0.2
QM12FFy 22.9 0.2
QM11FFx 25.6 0.2
QM11FFy 26.0 0.4


This time, the input RF is set to 2.890GHz and again, a variable attenuator is used.



Bpm Gain/dB Error/dB
SF1FFx 9.2 0.2
SF1FFy 2.8 0.3
SD0FFx 9.4 0.2
SD0FFy 9.8 0.2

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Topic revision: r4 - 28 Feb 2011 - FrankieCullinan

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