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Since putting this project on Youtube I’ve had a surprising amount of interest from across the world about the modifications I made to the original code from ON1ARF ( a radioamateur in België) to allow 1200 and 2400 bps pager transmissions as well as the default 512bps (I wanted to use the circuit to test commercial POCSAG pager receivers used at one site at my work).
The original code is here
https://github.com/on1arf/pocsag
To get 1200 and 2400 bps you must alter the radiohead libraries it depends on.
Two files must change – the first is RH_RF22.cpp. The code snippet is below (cut and paste this into your editor)
header file for Arduino POCSAG RF22 tx
// These are indexed by the values of ModemConfigChoice
// Canned modem configurations generated with
// http://www.hoperf.com/upload/rf/RH_RF22B%2023B%2031B%2042B%2043B%20Register%20Settings_RevB1-v5.xls
// Stored in flash (program) memory to save SRAM
PROGMEM static const RH_RF22::ModemConfig MODEM_CONFIG_TABLE[] =
{
{ 0x2b, 0x03, 0xf4, 0x20, 0x41, 0x89, 0x00, 0x36, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x10, 0x62, 0x2c, 0x00, 0x08 }, // Unmodulated carrier
{ 0x2b, 0x03, 0xf4, 0x20, 0x41, 0x89, 0x00, 0x36, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x10, 0x62, 0x2c, 0x33, 0x08 }, // FSK, PN9 random modulation, 2, 5
// All the following enable FIFO with reg 71
// 1c, 1f, 20, 21, 22, 23, 24, 25, 2c, 2d, 2e, 58, 69, 6e, 6f, 70, 71, 72
// FSK, No Manchester, Max Rb err <1%, Xtal Tol 20ppm
{ 0x2b, 0x03, 0xf4, 0x20, 0x41, 0x89, 0x00, 0x36, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x10, 0x62, 0x2c, 0x22, 0x08 }, // 2, 5
{ 0x1b, 0x03, 0x41, 0x60, 0x27, 0x52, 0x00, 0x07, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x13, 0xa9, 0x2c, 0x22, 0x3a }, // 2.4, 36
{ 0x1d, 0x03, 0xa1, 0x20, 0x4e, 0xa5, 0x00, 0x13, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x27, 0x52, 0x2c, 0x22, 0x48 }, // 4.8, 45
{ 0x1e, 0x03, 0xd0, 0x00, 0x9d, 0x49, 0x00, 0x45, 0x40, 0x0a, 0x20, 0x80, 0x60, 0x4e, 0xa5, 0x2c, 0x22, 0x48 }, // 9.6, 45
{ 0x2b, 0x03, 0x34, 0x02, 0x75, 0x25, 0x07, 0xff, 0x40, 0x0a, 0x1b, 0x80, 0x60, 0x9d, 0x49, 0x2c, 0x22, 0x0f }, // 19.2, 9.6
{ 0x02, 0x03, 0x68, 0x01, 0x3a, 0x93, 0x04, 0xd5, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x09, 0xd5, 0x0c, 0x22, 0x1f }, // 38.4, 19.6
{ 0x06, 0x03, 0x45, 0x01, 0xd7, 0xdc, 0x07, 0x6e, 0x40, 0x0a, 0x2d, 0x80, 0x60, 0x0e, 0xbf, 0x0c, 0x22, 0x2e }, // 57.6. 28.8
{ 0x8a, 0x03, 0x60, 0x01, 0x55, 0x55, 0x02, 0xad, 0x40, 0x0a, 0x50, 0x80, 0x60, 0x20, 0x00, 0x0c, 0x22, 0xc8 }, // 125, 125
// { 0x2b, 0x03, 0xa1, 0xe0, 0x10, 0xc7, 0x00, 0x09, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x04, 0x32, 0x2c, 0x22, 0x04 }, // 512 baud, FSK, 2.5 Khz fd for POCSAG compatibility
{ 0x27, 0x03, 0xa1, 0xe0, 0x10, 0xc7, 0x00, 0x06, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x09, 0xd5, 0x2c, 0x22, 0x07 }, // 1200 baud, FSK, 4.5 Khz fd for POCSAG compatibility
// { 0x27, 0x03, 0xa1, 0xe0, 0x10, 0xc7, 0x00, 0x06, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x04, 0x32, 0x2c, 0x22, 0x07 }, // 512 baud, FSK, 4.5 Khz fd for POCSAG compatibility
// 2400 bps
{ 0x27, 0x03, 0xa1, 0xe0, 0x10, 0xc7, 0x00, 0x06, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x13, 0xa9, 0x2c, 0x22, 0x07 },// 2400 baud, FSK, 4.5 Khz fd for POCSAG compatibility
// GFSK, No Manchester, Max Rb err <1%, Xtal Tol 20ppm
// These differ from FSK only in register 71, for the modulation type
{ 0x2b, 0x03, 0xf4, 0x20, 0x41, 0x89, 0x00, 0x36, 0x40, 0x0a, 0x1d, 0x80, 0x60, 0x10, 0x62, 0x2c, 0x23, 0x08 }, // 2, 5
{ 0x1b, 0x03, 0x41, 0x60, 0x27, 0x52, 0x00, 0x07, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x13, 0xa9, 0x2c, 0x23, 0x3a }, // 2.4, 36
{ 0x1d, 0x03, 0xa1, 0x20, 0x4e, 0xa5, 0x00, 0x13, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x27, 0x52, 0x2c, 0x23, 0x48 }, // 4.8, 45
{ 0x1e, 0x03, 0xd0, 0x00, 0x9d, 0x49, 0x00, 0x45, 0x40, 0x0a, 0x20, 0x80, 0x60, 0x4e, 0xa5, 0x2c, 0x23, 0x48 }, // 9.6, 45
{ 0x2b, 0x03, 0x34, 0x02, 0x75, 0x25, 0x07, 0xff, 0x40, 0x0a, 0x1b, 0x80, 0x60, 0x9d, 0x49, 0x2c, 0x23, 0x0f }, // 19.2, 9.6
{ 0x02, 0x03, 0x68, 0x01, 0x3a, 0x93, 0x04, 0xd5, 0x40, 0x0a, 0x1e, 0x80, 0x60, 0x09, 0xd5, 0x0c, 0x23, 0x1f }, // 38.4, 19.6
{ 0x06, 0x03, 0x45, 0x01, 0xd7, 0xdc, 0x07, 0x6e, 0x40, 0x0a, 0x2d, 0x80, 0x60, 0x0e, 0xbf, 0x0c, 0x23, 0x2e }, // 57.6. 28.8
{ 0x8a, 0x03, 0x60, 0x01, 0x55, 0x55, 0x02, 0xad, 0x40, 0x0a, 0x50, 0x80, 0x60, 0x20, 0x00, 0x0c, 0x23, 0xc8 }, // 125, 125
// OOK, No Manchester, Max Rb err <1%, Xtal Tol 20ppm
{ 0x51, 0x03, 0x68, 0x00, 0x3a, 0x93, 0x01, 0x3d, 0x2c, 0x11, 0x28, 0x80, 0x60, 0x09, 0xd5, 0x2c, 0x21, 0x08 }, // 1.2, 75
{ 0xc8, 0x03, 0x39, 0x20, 0x68, 0xdc, 0x00, 0x6b, 0x2a, 0x08, 0x2a, 0x80, 0x60, 0x13, 0xa9, 0x2c, 0x21, 0x08 }, // 2.4, 335
{ 0xc8, 0x03, 0x9c, 0x00, 0xd1, 0xb7, 0x00, 0xd4, 0x29, 0x04, 0x29, 0x80, 0x60, 0x27, 0x52, 0x2c, 0x21, 0x08 }, // 4.8, 335
{ 0xb8, 0x03, 0x9c, 0x00, 0xd1, 0xb7, 0x00, 0xd4, 0x28, 0x82, 0x29, 0x80, 0x60, 0x4e, 0xa5, 0x2c, 0x21, 0x08 }, // 9.6, 335
{ 0xa8, 0x03, 0x9c, 0x00, 0xd1, 0xb7, 0x00, 0xd4, 0x28, 0x41, 0x29, 0x80, 0x60, 0x9d, 0x49, 0x2c, 0x21, 0x08 }, // 19.2, 335
{ 0x98, 0x03, 0x9c, 0x00, 0xd1, 0xb7, 0x00, 0xd4, 0x28, 0x20, 0x29, 0x80, 0x60, 0x09, 0xd5, 0x0c, 0x21, 0x08 }, // 38.4, 335
{ 0x98, 0x03, 0x96, 0x00, 0xda, 0x74, 0x00, 0xdc, 0x28, 0x1f, 0x29, 0x80, 0x60, 0x0a, 0x3d, 0x0c, 0x21, 0x08 }, // 40, 335
};
Also the header file RH_RF22.h must change so the modemconfig table has values that reflect the changed modulation schemes.
typedef enum
{
UnmodulatedCarrier = 0, ///< Unmodulated carrier for testing
FSK_PN9_Rb2Fd5, ///< FSK, No Manchester, Rb = 2kbs, Fd = 5kHz, PN9 random modulation for testing
FSK_Rb2Fd5, ///< FSK, No Manchester, Rb = 2kbs, Fd = 5kHz
FSK_Rb2_4Fd36, ///< FSK, No Manchester, Rb = 2.4kbs, Fd = 36kHz
FSK_Rb4_8Fd45, ///< FSK, No Manchester, Rb = 4.8kbs, Fd = 45kHz
FSK_Rb9_6Fd45, ///< FSK, No Manchester, Rb = 9.6kbs, Fd = 45kHz
FSK_Rb19_2Fd9_6, ///< FSK, No Manchester, Rb = 19.2kbs, Fd = 9.6kHz
FSK_Rb38_4Fd19_6, ///< FSK, No Manchester, Rb = 38.4kbs, Fd = 19.6kHz
FSK_Rb57_6Fd28_8, ///< FSK, No Manchester, Rb = 57.6kbs, Fd = 28.8kHz
FSK_Rb125Fd125, ///< FSK, No Manchester, Rb = 125kbs, Fd = 125kHz
FSK_Rb_1200Fd4_5, ///< FSK, No Manchester, Rb = 1200bs, Fd = 4.5kHz, for POCSAG compatibility
// FSK_Rb_512Fd4_5, ///< FSK, No Manchester, Rb = 512bs, Fd = 4.5kHz, for POCSAG compatibility
FSK_Rb_2400Fd4_5, ///< FSK, No Manchester, Rb = 2400bs, Fd = 4.5kHz, for POCSAG compatibility
GFSK_Rb2Fd5, ///< GFSK, No Manchester, Rb = 2kbs, Fd = 5kHz
GFSK_Rb2_4Fd36, ///< GFSK, No Manchester, Rb = 2.4kbs, Fd = 36kHz
GFSK_Rb4_8Fd45, ///< GFSK, No Manchester, Rb = 4.8kbs, Fd = 45kHz
GFSK_Rb9_6Fd45, ///< GFSK, No Manchester, Rb = 9.6kbs, Fd = 45kHz
GFSK_Rb19_2Fd9_6, ///< GFSK, No Manchester, Rb = 19.2kbs, Fd = 9.6kHz
GFSK_Rb38_4Fd19_6, ///< GFSK, No Manchester, Rb = 38.4kbs, Fd = 19.6kHz
GFSK_Rb57_6Fd28_8, ///< GFSK, No Manchester, Rb = 57.6kbs, Fd = 28.8kHz
GFSK_Rb125Fd125, ///< GFSK, No Manchester, Rb = 125kbs, Fd = 125kHz
OOK_Rb1_2Bw75, ///< OOK, No Manchester, Rb = 1.2kbs, Rx Bandwidth = 75kHz
OOK_Rb2_4Bw335, ///< OOK, No Manchester, Rb = 2.4kbs, Rx Bandwidth = 335kHz
OOK_Rb4_8Bw335, ///< OOK, No Manchester, Rb = 4.8kbs, Rx Bandwidth = 335kHz
OOK_Rb9_6Bw335, ///< OOK, No Manchester, Rb = 9.6kbs, Rx Bandwidth = 335kHz
OOK_Rb19_2Bw335, ///< OOK, No Manchester, Rb = 19.2kbs, Rx Bandwidth = 335kHz
OOK_Rb38_4Bw335, ///< OOK, No Manchester, Rb = 38.4kbs, Rx Bandwidth = 335kHz
OOK_Rb40Bw335 ///< OOK, No Manchester, Rb = 40kbs, Rx Bandwidth = 335kHz
} ModemConfigChoice;
the rest can then be used as normal – remember to alter the main Arduino sketch code to select these new bps rates.
NB: I am based in the UK/Europe; we always use wide deviation for POCSAG signals (although much other PMR traffic is now on narrow deviation).
If your country’s Communications Ministry requires narrow deviation to be used you will have to recalculate the modem settings using the spreadsheet referred to in the library files. (Its not as bad as it might seem; I had to use it to get the 1200/2400bps settings and I am not an RF nor a coding expert by any means)