ESP8266+SX178 POCSAG,message length

[shitra99]

hi, what is the limit on message length? I can't send more than 50 characters

[jgromes]

Interesting question - I don't actually know what is the maximum, I don't think the POCSAG specifies any limit. RadioLib too doesn't enforce any maximum length, but I will admit I have not tested any long messages.

[shitra99]

If you send 100 characters, 60 recived , if send 200 characters the esp8266 reboots

[jgromes]

I was not able to replicate the reboot you reported. Since you have not posted any actual code or serial output, it is very hard to help you.

I did see that PDW was not able to print out more than 45 characters (as can be seen below), but I suspect it is due to a limitation of that program.

1234567  14:57:18 15-06-24 POCSAG-2 NUMERIC  1200   TONE ONLY
1234567  14:57:20 15-06-24 POCSAG-1 NUMERIC  1200   0123456789*U -[]

1234567  14:57:22 15-06-24 POCSAG-4  ALPHA   1200   012345678901234567890123456789012345678901234

1234567  14:57:28 15-06-24 POCSAG-2 NUMERIC  1200   TONE ONLY
1234567  14:57:30 15-06-24 POCSAG-1 NUMERIC  1200   0123456789*U -[]

1234567  14:57:32 15-06-24 POCSAG-4  ALPHA   1200   012345678901234567890123456789012345678901234

[shitra99]

45 characters is not a limitation of the program, try cap 100 and you will get 62 characters, cap 8 you will get 85 characters

[shitra99]

#include <RadioLib.h>

SX1278 radio = new Module(5, 4, 16, 15);

// create Pager client instance using the FSK module
PagerClient pager(&radio);

void setup() {
Serial.begin(9600);

// initialize SX1278 with default settings
Serial.print(F("[SX1278] Initializing ... "));
int state = radio.beginFSK();

// when using one of the non-LoRa modules
// (RF69, CC1101, Si4432 etc.), use the basic begin() method
// int state = radio.begin();

if(state == RADIOLIB_ERR_NONE) {
Serial.println(F("success!"));
} else {
Serial.print(F("failed, code "));
Serial.println(state);
while(true);
}

// initialize Pager client
Serial.print(F("[Pager] Initializing ... "));
// base (center) frequency: 434.0 MHz
// speed: 1200 bps
state = pager.begin(159.200, 1200);
if(state == RADIOLIB_ERR_NONE) {
Serial.println(F("success!"));
} else {
Serial.print(F("failed, code "));
Serial.println(state);
while(true);
}
}

void loop() {
Serial.print(F("[Pager] Transmitting messages ... "));

// finally, let's transmit an ASCII message now
int state = pager.transmit("1234567890123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890", 100, RADIOLIB_PAGER_ASCII);
delay(500);

// we can also send only a tone

if(state == RADIOLIB_ERR_NONE) {
Serial.println(F("success!"));
} else {
Serial.print(F("failed, code "));
Serial.println(state);
}

// wait for a second before transmitting again
delay(60000);
}

[shitra99]

sent 100 characters, received 62

[jgromes]

I don't have those devices, so I can't replicate this bhavior (as shown in my previous post). But this is an open-source project, so feel free to dig into the sources - pull requests containing bugfixes are always welcome.

[shitra99]

In transmission mode, need to connect pins DIO0 and DIO1? it works without them. And I found in the comments in file SX127x_FSK_Modem.ino "// NOTE: FSK modem maximum packet length is 63 bytes!", is this not the reason for the transmission limit of 62 characters?

[jgromes]

In transmission mode, need to connect pins DIO0 and DIO1?

Strictly speaking, for POCSAG transmission you don't need these pins. However, for all otehr transmissions using SX127x, at least DIO0 is required.

is this not the reason for the transmission limit of 62 characters

It is not, POCSAG transmission is not done using SX127x packet engine and FIFO which is where that 63 byte limitation comes from. In fact the 62 characters you are receiving do not correspond to 62 bytes being sent over the air, but much more due to encoding.

[shitra99]

there are inaccuracies when forming packets, when using CAP code 100, 62 characters are accepted, this is 2 batches. If you make CAP in the zero frame (for example 8) it will accept 23 characters more, part of the first batch is filled with empty words (ıdle words) so that CAP 100 gets into the 4th frame. i.e. in theory the encoder either inserts an ıdle word at the end of the second batch or does not start the 3rd batch with a sync word, if the CAP is 1234567, it recive

45 characters