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Gold Apollo AF-A27 / AL-A27



Galaxy

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

The Gold Apollo AF-A27 (FLEX) and AL-A27 (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.

Apollo AF-A27 ('Galaxy' in the Netherlands)

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 sdisabled to open the receiver continuously. Obviously, as a result battery life will decrease considerably.

This pin is cut
This pin is cut
This pin..
..and this pin need to be cut or removed
Three important spots
Follow the next steps to make a data output on the AF-A27 / AL-A27:
  • Cut the two pins with side cutters. This disables the connection between the microprocessor on the bottom printed circuit board from sending battery saving commands to the receiver
  • Using a piece of insulated wire, connect point 'A' with point 'B'. This puts a HI state on pin 17 of the receiver IC, which opens the receiver continuously
  • Connect point 'C' to point 'A' using a 1.2 k resistor. 'C' 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 'C'.
  • Connect the other pin of the 10 k resistor to the inner conductor of a strand of shielded wire. Connect the shield to ground
Three important spots
BS high
Discriminator output
Connecting points A and B enables continuous reception
The discriminator output at point C

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.

Eindresultaat
 
The result: pager with pigtail


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