Can WHDG18101G Replace WHDG18110G? Loss, Pinout and Height Checks for 18-Pin Gigabit LAN Transformers | VOOHU
Can WHDG18101G Replace WHDG18110G? Loss, Pinout and Height Checks for 18-Pin Gigabit LAN Transformers | VOOHU
Can gigabit LAN transformers be replaced directly when both parts are single-port, 18-pin DIP devices with a 1.78 mm pitch? Those matching labels are a useful starting point, but they do not prove interchangeability. Insertion-loss limits, return-loss test points, internal pin connections, centre-tap use and component height can all change the result on the board. WHDG18110G and WHDG18101G share many basic specifications, making them a practical comparison. A safe replacement decision still requires the electrical limits, schematic and PCB footprint to be checked together.
Can gigabit LAN transformers be replaced directly? Separate common specifications from real differences
WHDG18110G and WHDG18101G are both single-port 100/1000 Base-T LAN transformers. Each uses an 18-pin through-hole package with a 1.78 mm pitch, operates from 0 to +70°C, provides 1500 Vrms isolation and is specified as non-PoE. These shared conditions place the two products in a similar class of indoor Gigabit Ethernet ports and justify a closer comparison.
The shared headline parameters do not make the products automatic drop-in replacements. WHDG18101G gives insertion loss as a fixed limit, whereas WHDG18110G uses segmented and formula-based limits. Their nominal heights are also different: 3.20 ± 0.50 mm and 2.60 ± 0.50 mm respectively. Their return-loss requirements are presented differently as well. Every winding pin, centre tap and cable-side connection must match the original circuit.
An 18-pin count does not replace the pin table
Confirm component height, package and PCB hole pattern
DIP construction, 18 pins and 1.78 mm pitch narrow the search, but the nominal height of WHDG18101G is 3.20 ± 0.50 mm, compared with 2.60 ± 0.50 mm for WHDG18110G. That 0.60 mm nominal difference matters under a tight enclosure, airflow guide or upper PCB. Body length and width, row spacing, pin-one orientation, hole diameter and surrounding clearance must also agree with the assembly. Fit the sample to an unpowered board before electrical testing.
Map the PHY side, cable side and centre taps pin by pin
A LAN transformer contains several differential windings and centre taps. The same total pin count is not enough to skip a pin-by-pin comparison. Place the internal schematics of the original and candidate products side by side. Identify the PHY and cable sides first, then check every differential pair, centre tap and unused pin. Update the schematic symbol and PCB footprint together so that drawing and pad numbers cannot diverge.
Compare insertion loss at the same frequency
Insertion loss describes how much the signal is attenuated as it passes through the transformer. A common mistake is to compare one fixed figure with a formula covering a frequency range, or to use a low-frequency value as the answer for the whole Gigabit band. Define the frequencies required by the project, then express both products' limits at those same frequencies and with the same sign convention.
WHDG18101G specifies a maximum insertion loss of -1.1 dB from 1 to 100 MHz. WHDG18110G specifies -1.2 dB maximum from 0.5 to 1 MHz and uses -0.2 - 0.002 × f^1.4 dB from 1 to 125 MHz, where f is in MHz. Expressed as loss magnitude, the WHDG18110G formula gives approximately 0.68 dB at 50 MHz and 1.46 dB at 100 MHz. These are calculated limits, not typical measurements from a sample.
| Frequency | WHDG18101G IL limit | WHDG18110G formula limit (approx.) |
|---|---|---|
| 10 MHz | -1.1 dB Max | -0.25 dB Max |
| 50 MHz | -1.1 dB Max | -0.68 dB Max |
| 80 MHz | -1.1 dB Max | -1.12 dB Max |
| 100 MHz | -1.1 dB Max | -1.46 dB Max |
The same-frequency comparison shows why the two products cannot be considered electrically identical from their package labels. At 100 MHz, their stated insertion-loss limits are different. If the existing acceptance sheet says only “insertion loss: pass” without a frequency, add the required frequency, impedance, fixture and limit direction before approving a replacement.
Review return loss across the band, not at one convenient point
Return loss describes impedance matching at the port. WHDG18101G specifies -18 dB Min from 1 to 30 MHz, -14.4 dB Min at 40 MHz, -13.1 dB Min at 50 MHz, -12 dB Min from 60 to 80 MHz and -10 dB Min at 100 MHz. WHDG18110G specifies -16 dB Min from 1 to 40 MHz and -10 + 20 × log(f/80) dB Min from 40.1 to 100 MHz. The two formats must be compared at the same frequencies.
| Frequency | WHDG18101G RL limit | WHDG18110G RL limit (approx.) |
|---|---|---|
| 10 MHz | -18 dB Min | -16 dB Min |
| 50 MHz | -13.1 dB Min | -14.08 dB Min |
| 80 MHz | -12 dB Min | -10 dB Min |
| 100 MHz | -10 dB Min | -8.06 dB Min |
The table preserves each product's negative-value and Max/Min convention and is only a frequency-by-frequency comparison of component limits. Insertion loss can be an input to a loss budget, while return loss must be checked against its frequency mask; the two are not added together. Board-level return loss is also affected by PHY termination, differential routing, vias, the RJ45 connector and the fixture, so verify the result on the target PCB.
Match the centre taps to the power architecture
WHDG18110G and WHDG18101G are non-PoE products. Their centre taps are not assigned a DC balance-current capability and must not be used as a power path over the cable. If the port requires PoE, select a LAN transformer with an explicit PoE current rating instead of asking either of these products to carry undefined DC current.
A non-PoE port still requires the centre taps to be terminated correctly. Resistance, decoupling and grounding should follow the reference design for the selected PHY, with symmetry maintained across all differential channels. Reusing an old termination without checking the PHY recommendation can mix a circuit issue with a component-selection issue and make debugging unnecessarily difficult.
How to choose between two VOOHU 18-pin Gigabit LAN transformers
The VOOHU 100/1000 Base-T LAN transformer range includes products with different packages, port counts and electrical-limit formats. WHDG18101G suits an 18-pin through-hole port whose acceptance table is based on fixed frequency points. WHDG18110G suits a design that evaluates insertion- and return-loss limits at the actual frequencies of interest. The right choice is the product whose limit format, pin map and mechanical structure match the existing PHY, PCB and test plan.
| Project condition | VOOHU product | Selection and validation focus |
|---|---|---|
| Single-port Gigabit, 18-pin DIP, non-PoE; fixed-point acceptance table | WHDG18101G | IL is -1.1 dB Max from 1 to 100 MHz; RL uses fixed points; nominal height is 3.20 ± 0.50 mm. Check pin mapping and PHY termination. |
| Single-port Gigabit, 18-pin DIP, non-PoE; frequency-based limit calculation | WHDG18110G | IL uses segmented and formula-based limits to 125 MHz; RL is segmented; nominal height is 2.60 ± 0.50 mm. Complete same-frequency and board validation. |
The two products also share the same OCL, DCR, turns ratio, crosstalk, common-mode rejection, isolation and temperature-range conditions. Use those common items to complete the initial screen, then concentrate the detailed comparison on insertion loss, return loss, internal wiring and mechanical dimensions. A design requiring operation below 0°C, PoE current or a different package should move directly to the appropriate product family.
A four-step LAN transformer replacement process
Step 1: Build a like-for-like comparison
Place data rate, port count, package, pin count, pitch, operating temperature, isolation voltage and PoE capability in one table. Eliminate products that fail those basic conditions. Then add insertion loss, return loss, OCL, turns ratio, DCR, crosstalk and common-mode rejection, with the test frequency and limit direction stated beside every value.
Step 2: Check the schematic and PCB
Map the PHY side, cable side, centre taps and channel order pin by pin. Confirm orientation, hole pattern and body clearance. Do not replace only the part name in the BOM; keep the schematic symbol, PCB footprint, assembly drawing and inspection documents on the same approved revision.
Step 3: Test both products under identical conditions
Build the original and candidate parts on the same PHY, RJ45, PCB, cable and test setup. Check power-up and link negotiation first, followed by insertion loss, return loss and the common-mode or immunity tests required by the project. Include short cable, maximum intended cable length, speed changes and operating temperature. This isolates product differences from changes in the test environment.
Step 4: Complete pilot-build and production checks
Passing an engineering sample is not the final release. Confirm wave-solder or manual-solder conditions, component height, assembly clearance, lot consistency and incoming-inspection limits. Freeze the approved product revision, drawings and test records before the pilot build so that an 18-pin similarity does not become an uncontrolled substitution.
Frequently Asked Questions
Are all 18-pin Gigabit LAN transformers drop-in replacements?
No. Pin count, DIP construction and pitch are only basic filters. The internal connections, body dimensions, insertion loss, return loss, centre taps, temperature range and PoE capability must all match, followed by validation on the target PCB.
Which has lower insertion loss, WHDG18110G or WHDG18101G?
The answer depends on frequency. WHDG18101G uses a fixed -1.1 dB maximum from 1 to 100 MHz, while WHDG18110G uses a formula from 1 to 125 MHz. Compare them at the same frequency; one figure cannot represent the entire band.
Can these two products be used in a PoE port?
No. Both are non-PoE products and their centre taps have no specified DC balance-current capability. Use a transformer with a defined PoE current rating and check current, DCR and temperature rise for the required power level.
Does a successful Ethernet link prove the replacement is complete?
Not by itself. Test the intended cable length, speed changes, sustained traffic and temperature, together with the project's insertion-loss, return-loss and EMC requirements. A short-cable room-temperature link does not represent every operating condition.
What should be provided to VOOHU for replacement support?
Provide the original product specification, target PHY, the LAN-transformer section of the schematic, PCB hole pattern and dimensions, data rate, temperature range, PoE requirement, and the existing test frequencies and limits. Complete inputs allow incompatible options to be removed quickly and make sample validation more efficient.
Conclusion
An 18-pin Gigabit LAN transformer replacement cannot be approved from the three matching labels “18 pin, DIP, 1.78 mm.” The loss limits at the same frequency, internal pin connections and centre-tap use must match as well. WHDG18110G and WHDG18101G both serve single-port non-PoE Gigabit links, but their limit formats differ, so same-frequency comparison and board-level validation remain necessary. VOOHU can review the target PHY, schematic, PCB and acceptance limits, recommend a suitable Gigabit LAN transformer and support sample evaluation.
