DM1801+MMDVMHOST - RT3S with alternative firmware = there is noise;
DM1801+MMDVMHOST - RT3S with factory firmware = there is noise;
DM1801+MMDVMHOST - RT3 = no noise;
DM1801+MMDVMHOST - DM1801 with alternative firmware = no noise
Perhaps this is due to the electronic volume control?
MD380 direct talk noise
Re: MD380 direct talk noise
I have confirmed your findings. The noise is still present when using the factory firmware.
This means that it is unlikely that we will be able to make any improvement with just firmware changes.
It may be possible to fix it with a hardware modification but that would take some time to investigate.
The slight difference when set to minimum volume found by VK3NET is just down to the way we are handling the volume control. The factory firmware probably turns off the amplifier at minimum volume, we do not do that. Either method does not make any difference to the noise at normal volume settings.
The problem is that the audio route is via the HRC6000 baseband chip for both FM and DMR and the volume is controlled by varying the gain settings in the HRC6000. The volume control knob is just a variable DC input to the processor. However there is also a direct connection connection from the FM receiver output via a muting circuit directly to the amplifier, with no volume control. Even though this is muted all of the time it appears that some audio leaks through and that is what you are hearing. Quite why this direct route is there is a bit of a mystery. As far as we can tell the factory firmware doesn't use it and we certainly don't. It may be a hang over from a previous design that may have had a real volume control.
Colin G4EML
This means that it is unlikely that we will be able to make any improvement with just firmware changes.
It may be possible to fix it with a hardware modification but that would take some time to investigate.
The slight difference when set to minimum volume found by VK3NET is just down to the way we are handling the volume control. The factory firmware probably turns off the amplifier at minimum volume, we do not do that. Either method does not make any difference to the noise at normal volume settings.
The problem is that the audio route is via the HRC6000 baseband chip for both FM and DMR and the volume is controlled by varying the gain settings in the HRC6000. The volume control knob is just a variable DC input to the processor. However there is also a direct connection connection from the FM receiver output via a muting circuit directly to the amplifier, with no volume control. Even though this is muted all of the time it appears that some audio leaks through and that is what you are hearing. Quite why this direct route is there is a bit of a mystery. As far as we can tell the factory firmware doesn't use it and we certainly don't. It may be a hang over from a previous design that may have had a real volume control.
Colin G4EML
Re: MD380 direct talk noise
Thanks Colin G4EML a lot for the effort on the testing and confirmation.G4EML wrote: ↑Sat Dec 17, 2022 6:02 pmI have confirmed your findings. The noise is still present when using the factory firmware.
This means that it is unlikely that we will be able to make any improvement with just firmware changes.
It may be possible to fix it with a hardware modification but that would take some time to investigate.
Colin G4EML
I understand this is not compatible with the DMR specification, but most simplex doing so. I guess there must be a reason?
It is hard to find other models on the market that support OpenGD except MD UV380 & RT3S currently. If there could be an option to enable/disable filling unused timeslot, that will benefit the users a lot and attract more attention.
VK3NET