Ferrite Bead Impedance Code vs Impedance Column: 527 of 531 Walsin Rows Agree, and the WQBD Series Agrees on Only 13 of 45

A ferrite bead impedance code in a Walsin part number should equal the Impedance column. We tested 576 rows. In seven series, 527 of 531 agree exactly. In the WQBD series only 13 of 45 do, and 29 more match the part number four rows above. The code is the evidence that something in that block has moved.

Venatech Limited, an authorised Walsin distributor in Hong Kong, holds the inductor export file published by Walsin Technology (Walsin), 5,410 rows after the QA row Test123999 is removed. Ferrite beads sit inside it, tagged with an ohm unit. We hold no Walsin bead datasheet, so the file is all we can show. Here we check it against itself: a bead part number carries its impedance as a three-digit code, and the file has an Impedance column, so the two can be compared on every row. Every part number below is real and every count can be repeated.

Can you read a Walsin ferrite bead’s impedance from its part number?

Yes, on 576 of 645 bead-family rows. We read the digits just before the packaging letters and applied the usual rule: two digits times a power of ten, in ohms at 100 MHz. 121 is 120 ohm, 601 is 600 ohm and 102 is 1,000 ohm. Then we compared the result with the Impedance (100MHz[Ω]) cell on the same row.

The 645 are the 641 rows tagged with an ohm unit plus four WQBD rows tagged as nanohenry, which we come to below. We excluded 69 that cannot be tested: 14 MHC parts with a long code format, 13 BIH and 10 WTBL whose three digits are an index not an impedance, 11 MCM and 7 HCM whose Impedance cell is zero, and 14 small power inductors tagged with an ohm unit (MPA 9, WLPN 5), which we covered in ferrite bead selection.

How many bead rows agree with the Impedance column?

527 of the 531 rows outside WQBD, which is 99.2 percent. We parsed every one of the 576 testable rows. Five series agree on every single row, and the four exceptions are isolated: two sit within one catalogue step, two are a factor of ten out, and none is part of a shifted block.

The cleanest family reads exactly. The MHC series has 150 testable rows and 150 matches. If the file were randomly wrong the exceptions would be everywhere. They are not. They sit in one place.

Where does the WQBD series stop agreeing with itself?

In 29 of its 45 rows, which sit four places out of line. The 45 WQBD part numbers are contiguous in the file, and when we line the Impedance cell up against the codes we find a pattern. 29 cells equal the impedance coded in the part number four rows above, 13 equal the impedance coded in their own row (one row satisfies both), and 4 are zero. We have not seen this counted anywhere: one series, 45 rows, an offset of exactly four.

Here is the evidence, in file order.

Two blocks line up: the 2012 K2U block, positions 16 to 20, and the 2012 HCU block that follows the shifted run. The 1005 and 1608 blocks, and the 3216, 3225 and 4516 tail, sit four rows late. A selector that filters on Impedance would return WQBD1005K2U102TP, a bead whose own part number says 1,000 ohm, for a 70 ohm search.

Do resistance and current follow the part number or the impedance cell?

The impedance cell. This is the check that tells you which side is wrong. In both shifted WQBD blocks large enough to test, DC resistance rises with the impedance cell, rank correlation 0.75 and 0.99, and falls as the part number’s own code rises, rank correlation minus 0.47 and minus 0.31. In the 26 other bead groups with enough rows to test, outside WQBD, resistance rises with the code in every group, lowest 0.54.

Look at WQBD1005K2U102TP. Its code says 1,000 ohm and its row says 0.15 ohm and 600 mA. Position 1, WQBD1005K2U700TP, codes 70 ohm and its row says 1.2 ohm and 150 mA. A 1,000 ohm bead with 0.15 ohm of resistance, next to a 70 ohm bead with 1.2 ohm, is the opposite of how those two quantities move together in every other bead block. The impedance and resistance cells of the shifted rows agree with each other. It is the part-number column they disagree with.

Why are four WQBD beads tagged as nanohenry inductors?

Because the first four rows of the block carry inductor-style data in the wrong place. The Unit cell reads nH, the Inductance cell reads 22, 27, 33 and 39, and the Impedance cell reads zero. The part numbers are WQBD1005K2U700TP, WQBD1005K2U121TP, WQBD1005K2U241TP and WQBD1005K2U601TP, which code 70, 120, 240 and 600 ohm. These four are the only WQBD rows tagged nH. A related unit problem, 32 small power parts tagged as beads, is in ferrite bead against inductor impedance.

The impedances 70, 120, 240 and 600 are exactly what positions 5 to 8 carry in their cells. So the four codes were shifted four places down, and what remains above them is a nanohenry record. Our earlier count that WQBD is 91.1 percent populated in the Impedance column is correct as far as it goes: 41 of 45 cells are filled. It simply did not ask whether the filled cells were on the right rows.

What should a selector do with a bead row it cannot trust?

State the disagreement and keep the original beside it. Our free cross-reference tool matches against Walsin’s published catalogue and states every difference from your original rather than hiding it behind a tick. For these rows the useful output is the code, the cell and the neighbouring rows side by side.

Paste up to 500 part numbers or drop an Excel or CSV, and read the mismatches first. For any bead, write down the impedance your part number states and check it against the Impedance cell before you trust either. The same self-check on inductors is in inductor part number inductance code. The whole line sits on the Walsin inductor page, beads included.

What is physically in Hong Kong is on ready stock: 1,125 part numbers as at 23 September 2026, a dated snapshot and not a live feed. We hold 28 Walsin datasheets, 451 pages, and none covers an inductor or a bead. We are at Unit 207, 2/F, Sun Ling Plaza, 30 On Kui Street, Fanling, N.T., Hong Kong, (852) 2628 4777. Specifications on this line must be confirmed against Walsin’s own site and qualified in your own circuit.

The short version

A Walsin bead part number carries its impedance as a three-digit code, and we compared it with the Impedance column on 576 rows. In seven series, 527 of 531 agree exactly, 99.2 percent, and the four exceptions are one-step ladder differences. In the WQBD series, 13 of 45 agree with their own row, 29 agree with the row four above, and 4 read zero while being tagged as 22 to 39 nH inductors. Resistance follows the impedance cell, not the part number, in both shifted blocks large enough to test. We are not calling this a product defect. We are saying that a bead filter on this series can return a part whose own number says 1,000 ohm for a 70 ohm search. Qualification stays with you.

Send us the bead lines off your bill of materials and we will return the published row for each one, with the code beside the cell. And a question back: when a distributor sells you the part number and not the row, which of the two have you been qualifying?

Frequently asked questions