| Products > Test Equipment |
| Teardown, Repair & Analysis of a Rohde & Schwarz FSH3 3.0GHz Spectrum Analyzer |
| << < (8/10) > >> |
| dianzimi:
yes |
| dianzimi:
yes |
| tonyM:
I think these 3 black parts (excluding input capacitor) at FSH3 input signal path are resistors, which are making Pi-pad attenuator. As you can see, TSMU (ver.1 and ver.2) lacks Pi-Pad attenuator. Only one Zero resistor (see pictures below): If you put Zero resistor in the right place (as in TSMU-ver.2), I think your FSH3 will work (if next components/ICs are OK), but the measured levels will not be correct. As I don't have FSH3, I will propose the following experimental approach for calculating the Pi-pad resistors values (and calibrating the instrument): 1. Put zero resistor at the input signal path 2. Plug-in signal generator with known level at RF-input 3. Check the level, measured by FSH3, and calculate the difference in dB 4. As you know the difference (and input impedance=50 ohm), use calculator https://www.pasternack.com/t-calculator-pi-attn.aspx to find the values of the resistors. |
| hgl:
There is an interesting detail, the pin 2 of the synthesizer chip is isolated on the TSMU version 2. (Not properly visible in the photo, you can see only a small piece of brown foil under the pin). This is not the case with version 1 and FSH3. On the photos you can not see whether the synthesizer chips of FSH3 and TSMU are really the same. |
| dianzimi:
who knows the components detail information in the red rectangle bellow??[img][img] |
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