paulears wrote:As for using the wrong data format, surely the repeater should reject it - a properly clocked signal is still as continuous signal. A repeater with a carrier on it's receive frequency cannot receive two at the same time - just the strongest with or without data content.
Wrong data format? What? The issue is timeslot incursion, not data formats.
DMR works by having two timeslots. There should not be any continuous carrier on the input of a DMR repeater. Ever. Even if two different users are transmitting, using both timeslots. There is still a guard time between the slots to allow for some change of distance of the mobile station and some amount of time inaccuracy. Using a radio that transmits in the other timeslot defeats the entire purpose of a TDMA system.
If a radio is transmitting a blank carrier the repeater will still be affected by this if another station is trying to transmit on that timeslot. The received signal will definitely have a higher average bit error rate (BER), if it can even be decoded at all.
paulears wrote:I'm still thinking that with solid state TX/RX switching, then software/firmware upgrades should be able to get the sync in order.
How can you avoid transmitting in the other timeslot when the PA simply is incapable of ramping down fast enough? Sync is not the issue.
paulears wrote:The dPMR system wins here. doesn't it with two parallel channels on different frequencies, DPMR can receive two channels at once and software select which one to hear, but surely on a repeater input it is one channel at a time unless sync accuracy allows two different sources to interleave?
No. A dPMR repeater uses 6.25KHz channels. That's half the bandwidth of the channels DMR uses. dPMR repeaters can only support one user at a time. The terminals for this type of system are cheaper because they don't need to have hardware capable of TDMA. The network cost is greater though, because instead of buying one 12.5KHz channel and one repeater, you have to buy two 6.25KHz channels and two repeaters (and either an extra antenna or other hardware to allow them to share one antenna) There is no interleaving of two signals on dPMR, it is an FDMA system. Not something like CDMA. A single dPMR repeater cannot receive two channels.
dPMR only wins if you need just one channel per site. Also in some cases, like for purely simplex radio communications, dPMR would be a much more appropriate standard to use than DMR.