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Digital Voice for Amateur Use - Discuss use of digital voice technologies on the amateur radio bands. This is to include technologies such as VoIP, P25, DMR/TRBO, NXDN, D-STAR, etc.

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  #1 (permalink)  
Old 06-28-2017, 2:27 PM
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Default DMR Talkaround technicalities

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!
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Old 06-28-2017, 7:25 PM
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The radio identifies as a radio. The only thing another radio sees is data from another radio.
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Old 06-29-2017, 6:34 AM
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So it does not care if it is identified as a mobile station or base station?
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Old 06-30-2017, 10:35 AM
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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?
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Old 06-30-2017, 11:01 AM
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The radios do not have a mechanism to know. What is your concern or use case? TT
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Old 06-30-2017, 11:59 AM
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Quote:
Originally Posted by TampaTyron View Post
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/...01v020201p.pdf
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Old 06-30-2017, 12:55 PM
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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.
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Old 07-01-2017, 4:06 PM
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Quote:
Originally Posted by 16b View Post
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/...01v020201p.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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Old 07-02-2017, 1:32 PM
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Here's a good explanation of FDMA versus TDMA...

Key Differences between FDMA vs. TDMA Technology

According to this article, without the repeater to synchronize the time slots, DMR simplex reverts to a single 12.5 kHz signal that - while still digital - does not utilize or recognize time slots.

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Old 07-02-2017, 3:19 PM
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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).
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Old 07-02-2017, 3:37 PM
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Quote:
Originally Posted by jonwienke View Post
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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