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Gold Apollo AF-A25 / AL-A25



AF-A25

An obsolete pager can be converted into a single channel receiver for paging monitoring by adding a discriminator output.

De (Gold Apollo) AF-A25 (FLEX) and AL-A25 (POCSAG) pagers contain a single chip paging receiver IC: the TA31149. The pins on this IC are separated only 0.65 mm. However, soldering to the IC is not necessary if you follow the instructions below.

Be advised that the receiver IC has a built-in 2 level slicer. This modification only works for 2-level paging.

AF-A25 / AL-A25

Each pager contains a battery saving mechanism. At regular intervals, the receiver is switched on briefly to check if there are messages. If not, the receiver will sleep until the next interval. To be able to use the pager as a monitoring receiver, this battery saving mechanism needs to be disabled to open the receiver continuously. Obviously, as a result battery life will decrease considerably.

Important spots
Follow the next steps to make a data output on the AF-A25 / AL-A25:
  • Connect the two solder pads at point A. This enables continuous reception
  • Connect point C to point B using a 1.2 k resistor. B is connected directly to pin 19 of the receiver IC. This is an open collector output, which makes a pull-up resistor necessary
  • Connect a 10 k resistor to B
  • Connect the other pin of the 10 k resistor to the inner conductor of a strand of shielded wire. Connect the shield to ground, e.g. to the negative battery contact
Three important spots
BS uitgeschakeld
Discriminatoruitgang
Connecting the solder pads enables continuous reception
The discriminator output at point B

As there is not enough clearance for a chassis socket, you can drill a hole and lead the shielded wire outside. You can use a tyrap as strain relief. The shielded wire can be terminated with a female 3.5 mm connector. This 'pigtail' enables using a 2 levelinterface or audio cable.

You can also box the pager and add a 1.5 Volt power supply. You can find a description here.



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