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| Picotest Injector Teardowns |
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| sixtimesseven:
--- Quote from: Jay_Diddy_B on May 21, 2020, 11:31:20 pm ---Hi group, been busy with KiCAD and Fusion 360. Any interest in this project: (Attachment Link) (Attachment Link) This is a blocking capacitor and bias injector. Regards, Jay_Diddy_B --- End quote --- Yes, very interesting indeed! Just found this thread. Great work! I made my own PSSR tester since the picotest unit was far to expensive for me. Ended up doing pretty much what Ti suggested: http://www.ti.com/lit/an/slaa414a/slaa414a.pdf?ts=1590175942099 |
| Jay_Diddy_B:
Hi, Let me share a few measurements made on the prototype: This is a picture of the prototype. It was milled on double sided FR4 PCB. The board is 100mm x 100mm 0 - 200MHz A DSA815-TG was used for the measurement. The setup was normalized with a BNC barrel connector. The Bias tee is almost perfectly flat in the frequency range 0 - 200MHz. This was confirmed using an HP3577A VNA 0 - 1.5GHz The frequency range was widened to 1.5 GHz There is a notch at 922MHz After a little while I realized what was causing this. I tested a BNC tee piece with an 8cm length of RG316 coax on one limb. This is the result: A notch at 625MHz This notch is when the open length of the line is 1/4 of wavelength. 3 x 10E8 /625 x 10E6 = 48cm 1/4 wavelength = 12cm velocity factor = 0.66 It kind of works out. At 922MHz wavelength = 3 x 10E8 / 922 x10E6 = 32cm quarter wavelength = 8cm Open circuit transmission line The resistor needs to be moved closer to the capacitors. Regards, Jay_Diddy_B |
| Jay_Diddy_B:
Hi, The bias line was cut in this location: And the measurement repeated: Same vertical scale 5dB/div Considerable improvement. Some of the other 'wiggles' will go away if I have more vias between the top and bottom planes. Regards, Jay_Diddy_B |
| Sighound36:
Hi Jay As with all things RF, some of the smallest movements generator some of the most obvious gains. Great work :-+ |
| Jay_Diddy_B:
Hi, I have continued to look at this. I have been thinking about the best way to connect the large number of capacitor in series / parallel and maintain a controlled impedance. PCB Design Prototype board The board was made from 0.062 FR4 on my LPKF Protomat c60. Board Assembly I inserted some of the 'via wires' Measurement I used an HP 8714 for the measurement: This is 3mHz to 3GHz 2dB/div. looking good!! Jay_Diddy_B |
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