Hi,
I'm in the midst of reverse engineering the output filter on a VHF RF amplifier. Air coiled inductors and SMT caps. Before I can get the schematic into Spice, I need the values. Thankfully, there is something printed on the caps, but I can't measure in circuit because of surrounding passives distorting the reading.
I'm using the link below as a reference guide to markings. It's comprehensive, but there's still a lot of guess work depending on who made the component and when.
http://www.iequalscdvdt.com/Markings_and_Codes.htmlThe SMT cap markings are: 330J, 470K, 100J.
The caps are about ~2mm across and tall, beige coloured.
If I've read them correctly, they're 33pF, 47pF and 10pF. The last letter indicates either tolerance or voltage (
which?).
There are also what look like old style wire wound resistors (brown, with black ends), mounted inside an inductor, with the marking '
10pM'. My best guess, these are caps also (creating a resonant tank), value 10pF, again the last letter tolerance or voltage.
Picture below.
https://images2.imgbox.com/0e/2a/0xBBI4G6_o.jpgCan anyone confirm the above?
The Inductors
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Other than desoldering the coils, is there any way of measuring them in circuit? Only way I can think of is to physically measure them and feed the dimensions w\turns into an inductor calculator. If that method introduces too much error, then I'll have to just desolder and measure out of circuit. Will a 100KHz LCR meter do the job, or am I going to need a Network Analyzer @ VHF frequency for the measurement? Guessing the latter, which makes it a bit tricky.
Thanks.