WHDG18110G Gigabit LAN Transformer

Evaluate the formula at the frequency you actually care about; do not carry a low-band figure across the whole range. The WHDG18110G specifies insertion loss in two segments: -1.2 dB max from 0.5 to 1 MHz, and -0.2-0.002×f^1.4 dB max from 1 to 125 MHz with f in MHz.

That form means the permitted loss grows with frequency, so link margin is tightest at the top of the band. Return loss is segmented the same way: -16 dB min from 1 to 40 MHz, and -10+20×log(f/80) dB min from 40.1 to 100 MHz. For worst-case analysis, take the value at the highest operating frequency of the target link.

Indoor Gigabit data ports with a component temperature between 0 °C and +70 °C, particularly designs whose link budget has to be worked out frequency by frequency. The WHDG18110G is an 18-pin DIP single-port 100/1000 BASE-T transformer without PoE, so the port needs local power.

Because its insertion and return loss are given as formulas rather than fixed limits, a designer can compute the permitted loss at each frequency of interest, which suits links where margin is tight enough to need that resolution. Other options are in the 10/100/1000 BASE-T range.

No. The datasheet assigns no DC balance current capability to the centre taps of the WHDG18110G, so they cannot be used as a supply path. Terminate them according to the reference design for the target PHY.