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boatbod / op25

Fork of osmocom OP25 by boatbod
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Smartnet & cqpsk vs fsk4 #200

Closed rfuchs closed 5 months ago

rfuchs commented 5 months ago

Hi,

Is there a reason why the smartnet NB FM demodulator is only enabled for fsk4 channels but not for cqpsk channels? See https://github.com/boatbod/op25/blob/master/op25/gr-op25_repeater/apps/p25_demodulator_dev.py#L531

I'm listening to https://www.radioreference.com/db/sid/861 and with fsk4 I get distorted digital audio but good FM, and with cqpsk I get good digital audio but no FM. Patching up that line to also allow cqpsk makes things work.

Is this an oversight or have I configured something wrong?

boatbod commented 5 months ago

The proper voice channel setup for Smartnet can be found in smartnet_example.json. Specifically the following parameters:     demod_type="fsk4"     filter_type="widepulse" If that's not getting you good digital audio, try changing filter_type="rc" and see if that helps.

I'm actually a little surprised that demod_type="cqpsk" works at all for digital audio since it is supposed to follow the P25 Phase 1 specs which mandate C4FM/FSK4 encoding.  The problem is, I've never seen an actual Motorola spec, just TIA-102 standards docs.

Let me know whether changing widepulse makes any difference. Graham

On 1/19/24 17:12, Richard Fuchs wrote:

Hi,

Is there a reason why the smartnet NB FM demodulator is only enabled for fsk4 channels but not for cqpsk channels? See https://github.com/boatbod/op25/blob/master/op25/gr-op25_repeater/apps/p25_demodulator_dev.py#L531

I'm listening to https://www.radioreference.com/db/sid/861 and with fsk4 I get distorted digital audio but good FM, and with cqpsk I get good digital audio but no FM. Patching up that line to also allow cqpsk makes things work.

Is this an oversight or have I configured something wrong?

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rfuchs commented 5 months ago

Yeah I tried with the default settings (fsk4/widepulse) first and that gave me very choppy audio. For some reason changing to cqpsk made it work. BUT fsk4/rc also seems to work perfectly. Solved, thanks!

boatbod commented 5 months ago

Do you know if your Smartnet system is simulcast?  Widepulse (for simulcast) increases the filter bandwidth vs the rc filter used by standard P25. GrahamOn Jan 21, 2024 1:13 PM, Richard Fuchs @.***> wrote: Yeah I tried with the default settings (fsk4/widepulse) first and that gave me very choppy audio. For some reason changing to cqpsk made it work. BUT fsk4/rc also seems to work perfectly. Solved, thanks!

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rfuchs commented 5 months ago

Do you know if your Smartnet system is simulcast?  Widepulse (for simulcast) increases the filter bandwidth vs the rc filter used by standard P25.

No idea. Is there a way I can tell? Otherwise I only know what's listed on RR.