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Picotest Injector Teardowns

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Sighound36:
Pretty respectable trace there for a 3Ghz bandwidth  :)

Ok not being an RF guy, so shoot me  :-DD, would it not be better to have less capacitors with a larger value? Or is this a fundamental issue with this portion of the design?

Jay_Diddy_B:

--- Quote from: Sighound36 on May 27, 2020, 03:47:17 pm ---Pretty respectable trace there for a 3Ghz bandwidth  :)

Ok not being an RF guy, so shoot me  :-DD, would it not be better to have less capacitors with a larger value? Or is this a fundamental issue with this portion fot he design?

--- End quote ---

The capacitors I used are each 10uF 50V X5R 1210. The idea of such a high value is to get a low frequency -3dB point.

12 x 10uF / 2 = 60uF

R= 25 \$\Omega\$

F = 1/(2  x Pi x R x C) = 26.5 Hz

Regards,
Jay_Diddy_B

Jay_Diddy_B:
Hi,
Here are some TDR measurements  made with a Tektronix 11801 and SD24 sampling head.
The Bias injector was place between two lengths of semi-rigid 50 \$\Omega\$ cables:





From left to right

The 50 Ohm cable
the first 'wiggle' is the transition from the cable to the board, the SMA edge launch.
Then a short piece of 50 Ohm track.
two sections of 45 Ohms, about 25mm long, where the capacitors are
50 Ohm track
SMA connector
50 Ohm cable


I have marked the measured impedances on this drawing of the board assembly:



to raise the impedance where the capacitor are, I need to widen the gap between the traces and the ground plane.

Regards,
Jay_Diddy_B

Sighound36:
In a very crude way that is the situation I was attempting to elude to  :-[

Great stuff Jay, really do not know where you find the time but top man  8)

2N3055:
Nice demonstration of usefulness of TDR..

Great work (as always!!) Jay..

Regards,

Sinisa

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