Tapper or power splitter? Distributing the signal in an in-building network
Updated · Bandercom Oy
The power entering an in-building network's trunk line has to be shared among the antennas so that each one gets its planned power. There are two basic tools for that: the power splitter, which divides power equally, and the tapper (asymmetric power splitter), which takes only the share it needs from the trunk.
This page covers how each works, when to use which, and what the same corridor looks like with each. At the end there is an interactive circuit diagram where you can calculate your own line with the loss rules of the ST card attenuation form, with BDC's guaranteed values shown beside them.
A power splitter divides power equally
A power splitter divides the incoming power equally between all its outputs. In theory each output of a splitter with two outputs gets half the power, a 3 dB drop. Splitting three ways drops about 4.8 dB and four ways 6 dB. The real loss is slightly higher because the splitter also has losses of its own.
BDC states splitter loss as a guaranteed maximum that includes both the split and the losses. A splitter is the right choice when the branches need the same power: for example when a trunk is divided between the wings of a floor, or when every antenna gets its own cable from the equipment room.
| Model | Outputs | Insertion loss |
|---|---|---|
| BX-PS-02-43F | 2 | ≤ 3.3 dB |
| BX-PS-03-43F | 3 | ≤ 5.3 dB |
| BX-PS-04-43F | 4 | ≤ 6.6 dB |
A tapper takes only the share it needs
A tapper is an asymmetric power splitter. Its coupled port takes a small share of the trunk power to an antenna branch, and its through port passes the rest on. The coupling value says how much lower the branch power is than the trunk power: a 10 dB tapper sends a tenth of the power to the branch.
The higher the coupling value, the less the trunk power drops at the tapper. BDC states this through-loss as a guaranteed maximum. In a tapper chain the trunk runs past the antennas and every antenna gets its own tapper: high coupling values near the start, where power is plentiful, and low ones near the end. The last antenna is often connected straight to the end of the trunk.
| Model | Coupling | Through-loss |
|---|---|---|
| BX-PT-05-43F | 4.8 dB | ≤ 2.3 dB |
| BX-PT-06-43F | 6 dB | ≤ 1.75 dB |
| BX-PT-07-43F | 7 dB | ≤ 1.35 dB |
| BX-PT-08-43F | 8 dB | ≤ 1.25 dB |
| BX-PT-10-43F | 10 dB | ≤ 0.8 dB |
| BX-PT-13-43F | 13 dB | ≤ 0.5 dB |
| BX-PT-15-43F | 15 dB | ≤ 0.45 dB |
| BX-PT-20-43F | 20 dB | ≤ 0.4 dB |
| BX-PT-30-43F | 30 dB | ≤ 0.3 dB |
Which one, when?
- Tapper chain: a long corridor, car park, stairwell or any space where the antennas are in a row. Little cable is needed because the trunk runs past the antennas.
- Power splitter: when the trunk is divided into branches that need the same power, such as the wings of a floor or parts of a building, and when every antenna should have its own cable.
- Both: real networks use the two together. A splitter divides the trunk into sections, and tappers distribute each section to its antennas.
- Unused ports are always terminated with a load so the signal isn't reflected back into the network.
Example: 6 antennas along a corridor
A corridor has 6 antennas 15 metres apart, each on a 3 m branch cable. The trunk is fed with 30 dBm, and every antenna should get at least 10 dBm. Trunk cable loss is taken as 6 dB per 100 m and branch cable loss as 11 dB per 100 m, roughly 7/8 and 1/2 inch cable around 2 GHz. The example uses BDC's guaranteed maximum losses; the circuit diagram below uses the ST form's calculation values.
Tapper chain
| Antenna | Power at antenna | Part |
|---|---|---|
| 1 | 18.8 dBm | BX-PT-10-43F |
| 2 | 17.1 dBm | BX-PT-10-43F |
| 3 | 17.4 dBm | BX-PT-08-43F |
| 4 | 16.2 dBm | BX-PT-07-43F |
| 5 | 16.2 dBm | BX-PT-05-43F |
| 6 | 17.8 dBm | – |
- Power at antennas
- 16.2 dBm … 18.8 dBm
- Total cable
- 108 m
- Parts
- 2 × BX-PT-10-43F, 1 × BX-PT-08-43F, 1 × BX-PT-07-43F, 1 × BX-PT-05-43F
- Target
- All antennas ≥ 10.0 dBm
Splitter tree from the equipment room
| Antenna | Power at antenna | Part |
|---|---|---|
| 1 | 20.2 dBm | – |
| 2 | 19.3 dBm | – |
| 3 | 18.4 dBm | – |
| 4 | 17.5 dBm | – |
| 5 | 16.6 dBm | – |
| 6 | 15.7 dBm | – |
- Power at antennas
- 15.7 dBm … 20.2 dBm
- Total cable
- 333 m
- Parts
- 1 × BX-PS-02-43F, 2 × BX-PS-03-43F
- Target
- All antennas ≥ 10.0 dBm
Both designs meet the target. In the tapper chain the antennas get 16.2–18.8 dBm, using 108 m of cable. The splitter tree ranges from 15.7 to 20.2 dBm: the farthest antenna gets the least because its cable is the longest. It needs 333 m of cable, because every antenna gets its own run.
Circuit diagram: calculate your own line
Click a tapper or the splitter to swap it, a cable label to change its length, or the source to change its power. The drawing recalculates at once at 1800 MHz with the ST form's loss rules and shows an antenna green when the power reaching it is no more than 3 dB below the strongest antenna.
8 / 9 antennas in balance · AV-6 below the limit
Scroll the diagram sideways
- AV-1: 28.3 dBm, in balance
- AV-2: 30.1 dBm, in balance
- AV-3: 27.9 dBm, in balance
- AV-4: 27.9 dBm, in balance
- AV-5: 29.7 dBm, in balance
- AV-6: 27.1 dBm, more than 3 dB below the strongest (−3.7 dB)
- AV-7: 29.6 dBm, in balance
- AV-8: 30.8 dBm, in balance
- AV-9: 29.7 dBm, in balance
- Cable 7/8" 14m · 1/2" 138m · Parts 8
Show the calculation as a table
| Antenna | Power at antenna | State |
|---|---|---|
| AV-1 | 28.3 dBm | in balance |
| AV-2 | 30.1 dBm | in balance |
| AV-3 | 27.9 dBm | in balance |
| AV-4 | 27.9 dBm | in balance |
| AV-5 | 29.7 dBm | in balance |
| AV-6 | 27.1 dBm | more than 3 dB below the strongest (−3.7 dB) |
| AV-7 | 29.6 dBm | in balance |
| AV-8 | 30.8 dBm | in balance |
| AV-9 | 29.7 dBm | in balance |
| 8 / 9 antennas in balance · AV-6 below the limit | ||
| Cable 7/8" 14m · 1/2" 138m · Parts 8 | ||
| 1 × BX-PT-08-43F · 5 × BX-PT-05-43F · 1 × BX-PS-02-43F · 1 × BX-PT-10-43F | ||
The calculation follows the calculation rules of the ST card attenuation form (v1.5, 26.9.2026): a power splitter's loss is the theoretical split + 0.1 dB and a tapper's through-loss the theoretical value + 0.15 dB. BDC also states guaranteed maximum values, slightly above the calculation values: they give the worst case a part will not exceed. The 3 dB balance limit is design practice; the form highlights a difference above 6 dB. Radiation safety (EIRP limits) is not part of this circuit diagram.
| Model | Part | ST calculation value | BDC guaranteed maximum |
|---|---|---|---|
| BX-PT-05-43F | Tapper 4.8 dB, through-loss | 1.9 dB | ≤ 2.3 dB |
| BX-PT-06-43F | Tapper 6 dB, through-loss | 1.4 dB | ≤ 1.75 dB |
| BX-PT-07-43F | Tapper 7 dB, through-loss | 1.1 dB | ≤ 1.35 dB |
| BX-PT-08-43F | Tapper 8 dB, through-loss | 0.9 dB | ≤ 1.25 dB |
| BX-PT-10-43F | Tapper 10 dB, through-loss | 0.6 dB | ≤ 0.8 dB |
| BX-PT-13-43F | Tapper 13 dB, through-loss | 0.4 dB | ≤ 0.5 dB |
| BX-PT-15-43F | Tapper 15 dB, through-loss | 0.3 dB | ≤ 0.45 dB |
| BX-PT-20-43F | Tapper 20 dB, through-loss | 0.2 dB | ≤ 0.4 dB |
| BX-PT-30-43F | Tapper 30 dB, through-loss | 0.2 dB | ≤ 0.3 dB |
| BX-PS-02-43F | Power splitter, 2 outputs, loss | 3.1 dB | ≤ 3.3 dB |
| BX-PS-03-43F | Power splitter, 3 outputs, loss | 4.9 dB | ≤ 5.3 dB |
| BX-PS-04-43F | Power splitter, 4 outputs, loss | 6.1 dB | ≤ 6.6 dB |