g4klx
commented
7 years ago The problem of the MMDVM not responding to DMR transmissions immediately after the transmitter stops is known about. The answer is not simple, in MMDVM terms.
As people have already identified, the user radio thinks that the loss of signal is because of local interference or terrain and assumes that the repeater is still operational and behaves accordingly. It doesn’t send the normal wakeup CSBK, until a while later when it decides that the repeater really has closed down. This behaviour while understandable, isn’t mandated in the standard which is why I didn’t put it into the MMDVM. It didn’t help that I developed the software in a vacuum without access to a real DMR repeater to compare with. Thankfully the DMR specification is very complete (do you hear me Icom and Yaesu).
With the MMDVM, some major changes would need to be made to enable the same sort of operation. As written the transmitter switches on as soon as data is ready to be transmitted, with DMR not only is data generated that is transmitted, but also timing information which isn’t transmitted but sent back to the receiver to enable TDMA operation. Splitting the operation of the transmitter from the presence of data wouldn’t be too complex, and would be an MMDVM firmware-only issue. This would allow for the timing information to be sent back to the receiver to allow it to operate. You’d probably need to send the data to the DMR idle receiver also for safety. This state of affairs would only last for a few hundreds of milliseconds before switching to true Idle mode.
The host would also need to be modified to handle normal DMR data as well as Idle data when in Idle mode. This would be relatively easy too.
It would be an interesting project for someone to do!
I would do it, but I have limited free time and I have other priorities with the MMDVM, i.e. the YSF and P25 demodulators.
iw9grl
ok2it
vk4tux
ve2nbz
Hi dear, this is a question posted in Yahoo group :
One remaining issue affecting MMDVM in repeater operation is a "dead window" when the repeater should wake-up from "listening" status IMMEDIATELY after the ending of the TX hang time. This has been noticed in DMR mode on the two totally different repeaters we built for our ham club. This dead window is very narrow (perhaps ~200ms) but can randomly disrupt communication because the repeater doesn't wake up, and since the MS ( mobile station ) is still receiving the end of hang-time transmission, it assumes the repeater has waken-up so it keeps transmitting. When this happens, the whole voice message is lost.
Any solutions ? Tnx 73