DMR Talkaround technicalities

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DMRdude

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I have a couple of questions about how talkaround functions:

When a mobile radio keys up in talkaround mode, does it identify as a base station?
Further, does/can a receiver discriminate between a station type (Mobile/base) if it is on the correct frequency, color code and TG?

Thanks!
 

DMRdude

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So it does not care if it is identified as a mobile station or base station?
 

W2PDX

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Hi DMRdude. Just to clarify your question... you are referring to a radio transmitting on the repeater output frequency (bypassing the input frequency) when you mention "talk around" right?
 

16b

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The radios do not have a mechanism to know. What is your concern or use case? TT
Since there are significant differences between a DMR transmission from a base station and a mobile station (FDMA vs TDMA for starters), I would imagine that not only does the radio indeed have a mechanism to know, but that it *must* know and be able to distinguish between the two so that it can properly decode the transmission.

To the OP: the ETSI spec is probably the best reference for your question. It is freely available online.

http://www.etsi.org/deliver/etsi_ts/102300_102399/10236101/02.02.01_60/ts_10236101v020201p.pdf
 

DMRdude

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W2PDX, I am referring to when a radio transmits on a repeater output instead of input.

Thanks 16b, I'll look through it and post here if I find anything. To my scanner, my MD-390 in talk-around mode sounds identical to "repeater input" mode and DSD+ Identifies it as a mobile unit in both situations. This sounds nothing like a repeater output so if the MD-390 is fully compliant with the spec, there is no difference in the transmitted data.
 

KK4ELO

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Since there are significant differences between a DMR transmission from a base station and a mobile station (FDMA vs TDMA for starters), I would imagine that not only does the radio indeed have a mechanism to know, but that it *must* know and be able to distinguish between the two so that it can properly decode the transmission.

To the OP: the ETSI spec is probably the best reference for your question. It is freely available online.

http://www.etsi.org/deliver/etsi_ts/102300_102399/10236101/02.02.01_60/ts_10236101v020201p.pdf
So your saying that a base uses FDMA and a mobile uses TDMA? I'm sure we could all use some clarification on that. I thought FDMA was single channel/multiple frequency (trunking), and TDMA was single frequency/multiple channel split by time slots.

I guess grasshopper still has lots to learn about this stuff.

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jonwienke

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DMR always uses TDMA. In simplex mode, the slot number is ignored, but the digital signal for a voice channel is still broadcast 50% of the time using 100% of the frequency bandwidth (12.5KHz).

FDMA broadcasts the digital signal 100% of the time using 50% of the frequency bandwidth (6.25 KHz).
 

KK4ELO

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DMR always uses TDMA. In simplex mode, the slot number is ignored, but the digital signal for a voice channel is still broadcast 50% of the time using 100% of the frequency bandwidth (12.5KHz).

FDMA broadcasts the digital signal 100% of the time using 50% of the frequency bandwidth (6.25 KHz).
And ^ this is what I was thinking. I think some others got my post confused as I've had a couple trying to really explain it to me when I was being sarcastic. I guess Noone got the hint.

I was just pointing out the fact he was saying a mobile used one format while the other used a different format because one is a base and one is a mobile.

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