BT Eqmt Terminating No. 24A / 25A

This unit comprises two halves each which houses an Alarm Unit 85A and a Line Terminating Unit 11A / 1 / 2. It's inputs are twisted pairs but the outputs are on two BNC connectors. I suspect that it is a 2MB/s device, but this is a calculated guess based on BNC and the internal coax connectors being used for 2MB/s circuits elsewhere ( but also for 34MB/s ), and the twisted pair line side connections could carry 2MB/s with SDSL, but the circuitry on the LTU card doesn't seem sufficiently advanced to be SDSL. It certainly isn't 34MB/s capable.

The unit is in a 3u approx size case but is not rack mountable, instead it has keyholes cut in the bottom to allow wall mounting. Ite cover is a brown smoked perspex which is incredibly static sensitive, it collects charge at the least rub.

Each pair of PCBs has it's own connector panel, the coax I/O is on the rear, but the twisted pair connections are made via an IDC panel which is accessible by removing the top.

Line Terminating Unit 11A

This board seems to accept twisted pair I/O from the IDC connection board (lineside I think) and converts to a coax I/O for the subscriber side.

The lower half of the board seems to be a power supply section, the middle (presumably with sensitive components / processing filters etc) is covered with a soldered on screen so it is not possible to see that is under easily. The top half has an STC 5005 and a Texas Instruments chip, but I have been unable to find any data sheets. The crystal oscillator cans seem to provide clocking which is divisible easily, eg. 8.192 MHz (8192 → 4096 → 2048 → 1024 → 512 → 256 → 128 → 64 → 32 → 16 → 8 → 4 → 2 → 1Hz ).

Alarm Unit 85A

This board has a loop in and loop out for each of the RX and TX coax connections from the LTU11 board to the rear panel BNC. There are a set of relays immediately behind the coax sockets, presumably for some sort of monitoring / fail over. There are two pcb mounted pin plugs which seem to connect the the IDC connection PCB on the top and the 9 pin D socket on the rear. Maybe these are dry contacts from the relays for activating an external alarm.

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telecoms/bt-eqpt-term-24a-25a.txt · Last modified: 10/11/2022 00:17 by andrew