POCSAG wrong deviation

[dk5ras]

POCSAG requires 4.5 kHz deviation, but with MMDVM-IQ only about half the deviation is transmitted. Some Chinese pagers still work with this, many professional pagers don't. MMDVMHost with ADF 7021 transceiver has the correct deviation.

I am using SXceiver board on a RasPi 5.

DMR and P25 are just fine and work perfectly, good job!

[dk5ras]

I do not know if the configured level in POCSAGTX.cpp is the deviation in Hz - but increasing this from 1700 to 4500 makes the transmissions decodable.

[g4klx]

The value in POCSAGTX.cpp is not the deviation as an direct number, I mean 1700 does not mean 1700 Hz deviation. It does affect deviation though, and is linearly scaled with frequency. Could you try 2000, 2500, 3000, 3500, etc. (as well as the negative version of those values on the line below). You should be able to find a lower value than 4500 that works.

[dk5ras]

I will check the bandwidth with an analyzer and let you know the correct value, however this may take me somet time as I will travel a bit during the next days...

[dk5ras]

The inner peaks are the correct value from an ADF 7021 hotspot, the outer peaks with MMDVM-IQ and a value of 4500. So maybe about 4000 would be right. I will play a bit around...

BTW, the plain carrier peak left from the frequency is not very nice... :)

[dk5ras]

I could not stop, so I tried different values, and I would say, 3875 is the way to go!

[g4klx]

I have change the values to +-3875, I hope it now has the correct deviation.

[dk5ras]

So far it is OK now; however when the correct value can be calculated, it would be perfect - my value is not 100% precise, only try and error with a spectrum analyzer. I tried different values in steps of 25 until it looked good. At least it should be a few 100 Hz on the spot, so pagers will perform as intended.