===============================================================================
FREQUENTIES POCSAG                                      Bijgewerkt tot 15-05-96
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147.2500   512Bd  (100% Pocsag) Belgie
154.9875   512Bd  (100% Pocsag) Nederland Nationaal 1 ook BRANDWEER-OPROEPEN
159.9875   ?       
159.9900   ?                    Nederland Nationaal 2 Buzzing
160.0000   512Bd  (100%  " "  )
160.2275   1200Bd 
164.3500   512Bd  (100%  " "  ) Semafoon Benelux
166.3700   ?      ?
169.4000-169.7750 25 kHz step   ERMES Europees semafoonnet in 1996 aktief
171.1600   512Bd  (100%  " "  )
172.4500   1200Bd               Nederland Nationaal 3
460.91875  1200Bd               Nederland Callmax
465.9700    512Bd               Cityruf
466.0750   1200Bd               Internationaal Callmax
466.2300   1200Bd               Info/Scall

Als je daar eens luistert, dan heb je enig idee waar je op moet letten.
De signalen zijn ernorm hard.
Het klinkt als een hoop dof gerommel met behoorlijke harde modulatie.
Het 1200Bd Pocsag klinkt alsof het Packet is.
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Interfacing 

The PD program requires serial POCSAG data to be applied to the CTS pin  of 
one  of  the PC's COM ports. RS232 levels are required, ie at least +/- 3v.  
PD is insensitive to polarity, ie it doesn't matter which way up  mark  and 
space are.

As POCSAG is transmitted as direct FSK of the VHF/UHF carrier the ideal way 
is  to take the data direct from the discriminator, via a data slicer.  The 
following circuit,  however,  has  been  fairly  successful,  taking  audio 
directly from the receiver's speaker output:-

  0.1 uF                    |\ +12v
---||----------------------2|- \7
AF IN    |                  |741 \
----     |                  |    /6-------------------- Data Out
    |    \            -----3|+ /4  |                    CTS (pin 5/8)
    |    / 100K       |     |/-12v |
    |    \            |            |         GND ------ GND (pin 7/5)
   GND   /            ----/\/\/\---- 
         |            |   100K or             =================================
         |            \   470K potmeter by    N.B. Pin Numbers for com port are
        GND           /        discr. IN      given as x/y, where x is for a 25
                      \  10K or               way, y for a 9 way.
                      /  4K7 by discr. IN     =================================
                      |
                     GND      
		     
The  above circuit is a Schmitt Trigger, having thresholds of about +/- 1v. 
If such a large threshold is not required, eg for a  discriminator  output, 
then  the  level of positive feedback may be reduced by either reducing the 
value of the 10K resistor or by increasing the value of the  100K  feedback 
resistor.

The +/- 12v for the op-amp can be derived from unused signals  on  the  COM 
port (gives more like +/- 10v but works fine !):-

                                                                  on ic-pin 4
    TxD (2/3) --------------|<-------------------------------------- -12v
                                     |                  |
    RTS (4/7) --------------|<--------       GND (7/5)  - -
                   |                          |         _ +  10uF
                    --------->|-------        - -       |
                    Diodes 1N4148    |        - + 10uF  GND (7/5)
                                     |        |                   on ic-pin 7
    DTR (20/4) ------------->|-------------------------------------- +12v

