Finisar FTRJ8519P1BNL-B1
Finisar · SFP transceiver · FTRJ8519P1BNL-B1
what it is
An optical SFP transceiver made by Finisar, part number FTRJ8519P1BNL-B1. Units examined: 2.
It belongs to the same part number family as Finisar FTRJ8519P1BNL-C5 — the two differ in the part number suffix. Each model page describes only what we read from its own units.
what we read from it
The transceiver has optical diagnostics (DOM): the device reads temperature, supply voltage, laser bias current, transmit power and receive power from it. This makes an aging laser or a dirty connector visible before the link starts losing data.
Values from the 2026-10-24 reading in the UniFi Dream Machine Pro, two units with no fibre connected:
- temperature: 46–48 °C,
- supply voltage: 3.24–3.25 V,
- laser bias current: 4–5 mA,
- transmit power: −6.0 and −5.0 dBm,
- loss of signal (RX_LOS): raised on both units, transmitter fault (TX_FAULT): none.
Receive power without fibre says nothing about a link. One unit showed about −27 dBm, which is receiver noise, and the other reported no value at all. Here it is RX_LOS, not the dBm figure, that tells you the receive state.
what to watch for in the UniFi Dream Machine Pro
- A disabled SFP+ port does not show the transceiver. When the port is set to disabled, the UDM Pro reports the cage as empty even with a transceiver inserted. Both the UniFi controller and the device's internal API then show
present: false. After the port was enabled, both units appeared immediately, together with their diagnostics. ethtool -mdoes not work. In the UDM Pro shell the command fails with "Cannot get Module EEPROM data: Invalid argument". The transceiver identity and diagnostics are available through the UniFi controller or throughubios-udapi-client GET -r /interfaces(the interfacesfpsection).
how we checked
The result depends on what the transceiver was read with — the same switch model in a different installation can show different data. That is why each reading is recorded separately:
- UniFi Dream Machine Pro, firmware
5.1.33.34087— transceiver fields in the UniFi controller, 2026-10-24: diagnostics read (2 units). Visible data: temperature, supply voltage, laser bias current, transmit power, receive power, loss of signal indication (RX_LOS), transmitter fault indication (TX_FAULT), manufacturer, part number, serial number. Cable test: not tested.
The same transceiver in other switches and a comparison with other models: what each device shows.
what we cannot read
- Manufacturer alarm thresholds — the UniFi controller does not pass them on. The thresholds are in the transceiver memory; they are read by a switch that exposes the raw diagnostic memory page (e.g. Cisco Catalyst 2960-CX).
- Standard, revision, manufacturing date and wavelength — the UDM Pro did not report them; they are in the transceiver memory.
parameters the transceiver returns
The list shows WHAT the device exposes — including parameters we do not use ourselves. There are no values here at all: it is a catalog of capabilities, not a reading from anyone's network. It is not a closed list either — explanation below the table.
Parameter names are our internal identifiers and are in Polish (e.g. data_produkcji = manufacturing date, dlugosc_fali_nm = wavelength in nm); the type column describes each one in English.
10 parameters
| parameter | type |
|---|---|
moc_nadawana | number (dBm) |
moc_odbierana | number (dBm) |
napiecie_zasilania | number (V) |
numer_czesci | text — part number (PN) |
numer_seryjny | text |
prad_lasera | number (mA) |
producent | text — vendor name from transceiver memory |
temperatura | number (°C) |
usterka_nadajnika_tx_fault | boolean |
utrata_swiatla_rx_los | boolean |
This is not a closed list. It comes from reading a unit we had access to — it shows what we managed to retrieve, not everything the device can return. A different firmware version, hardware variant or reading path can expose fields that are not here. If you are interested in a specific unit and a specific value — please ask; there is a good chance it can be obtained, even if you do not see it below.
List source: reading of 2 working units (as of 2026-10-24). The list is the sum of what we observed — more units reveal more parameters, so numbers for different models are not directly comparable.