Is there a schematic for that probe somewhere on the web? Or does someone know what would be a good replacement for the main calibration variable cap it there? It's the red plastic one, SMT, square.
-- Regards, Joerg http://www.analogconsultants.com
I'd measure the capacitance on the scope end, add 10 pF for the scope, and then divide by 9 to match the voltage divider. That of course neglects other capacitance in the circuit, but for a trimmer it ought to be reasonably close.
Cheers,
Phil Hobbs
Yes, I'll probe it out if there is no schematic. But these things are way more complicated. IIRC there were several other trim caps and three potmeters or so in there. Plus some fixed value SMT components. The gold-plated BNC as well as the tip cable are clicked into slip ring holders. Quite impressive, actually.
At least I was able to finish the measurement by wedging a piece of toothpick in there. Not so with the baseband analyzer. It had been literally destroyed in shipping. Wanted to measure phase noise on VCSELs but I guess that has to wait now :-(
-- Regards, Joerg http://www.analogconsultants.com
I thought that the color of the variable capacitor's body told you its range? I've seen charts that told which color was what range, but its been a few years.
-- Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida
No idea. I am used to ceramic trim caps where the range is printed onto the base. But on my designs I never use any of that, it's all electronic auto-calibration so I haven't kept up with the fashion trends ;-)
-- Regards, Joerg http://www.analogconsultants.com
Might it be one of the muRata TZV4 series? Have a look at DigiKey
490-1980-1 and 490-1981-1; slightly different lead configurations of the same thing. 20pF max, 4.5pF min, N750 tempco.
Thanks, Tom. Those look a bit larger but could possibly fit. Next time I am at that client I'll unsolder one and measure it.
The 2nd P/N datasheet link resulted in an invalid part number. But that isn't anything new at Digikey. After they botched the search engine last time it hasn't been the same. There are times where just waiting a few hours fixes a link, then the next day it's broken again.
-- Regards, Joerg http://www.analogconsultants.com
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