MIF (ITF Control)
kiwamu.izumi - 15:57, Thursday 28 February 2019 (8247)
two RF outputs of the harmonic generator showing low RF power

Ryosuke, Yutaro, Kiwamu,

We discovered today that two out of ten RF outputs of the harmonic generator had appreciably low RF outputs. This issue may need to be addressed.

We figured this out when measuring the RF power at various points to determine the necessary RF attenuators as part of the demodulator checkout (klog 8231). We are wondering whether they have been low from the beginning.

Measurement summary

Here is a summary table of the RF power measured directly at the front panel of the harmonic generator (S1909724) at the IOO rack (D1706814-v9). The measurement values from the manufacturer can be seen in the same link.

Multiplication factor (names) measured RMS [mV] RF power [dBm] Measurement by the manufacturer [dBm] Difference from factory measurement [dB] Notes
x 2 880 11.90  13.5  -1.6  
x 3  (f1) 850 11.60  12.9  -1.3  
x 5 782 10.87  12.9  -2.03  
x 6  (2f1) 876 11.86  12.6  -0.74  
x 7 716 10.11  12.1  -1.99  
x 8 (f2) 615 8.79  13.0  -4.21  sad
x 9 (3f1) 892 12.02  13.4  -1.38  
x 10 756 10.58  13.2  -2.62  
x 16 (2f2) 427 5.62  12.6  -6.98  sad
x 30 760 10.63  13.5  -2.87  

Measurement setup

We used an oscilloscope, DSO-X 3054A, configured for DC coupling with a 50 Ohm input imepdance. The oscilloscope has an measurement bandwidth of 500 MHz and therefore we think all the measurements were valid. The RF signal was coupled to the oscilloscope via a 2-m long SMA cable with a BNC-SMA adapter at one of its ends to hook it up to the oscilloscope input. We also cross-checked the signal level by comparing a same RF signal against that measured with a MockLab which didn't show appreciable discrepancies at around 90 MHz.

The seed source for the harmonic generator is an N5181B, outputing a 5.624308 MHz sinusoidal signal with an amplitude of 10 dBm.

In addition, we performed another calibraion check where we plugged the oscilloscope directly to the seed source instead to the harmonic generator. It seems that the oscilloscope has a good enough calibration. The below is a summary of the calibration check.

Comments related to this report
ryousuke.sugimoto - 10:23, Friday 01 March 2019 (8260)

Attached images are waveform and spectrum of 3f2 signal obtain by mixing X30 and X6 (2f1).

The RMS of the signal is about 119 mV (-5.4dbm).

Originally, the mixing signal was passed through low pass filters (two of ZX75LP-137), but this image was measured by exchang them with a band pass filter (SXBP-140).