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Does DMR simplex use 1 time slot or 2?

dmaria

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DMR simplex, can be single timeslot. There are various names for this, including dual capacity direct mode (DCDM).
My post seems to have gone missing, so I'll ask again. Are you implying that DMR simplex does transmit on both time slots?
 

chief21

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My post seems to have gone missing, so I'll ask again. Are you implying that DMR simplex does transmit on both time slots?
It's my understanding that DMR simplex typically uses both time slots (unsynchronized - since no sync signal is available). However, the option to use Dual-Capacity, Direct Mode (DCDM - aka double-slot) is offered in some DMR radios.

As a side note, the time slot/sync issue appears to be the reason why the typical "repeater talk around" mode does not work with DMR.
 

jonwienke

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DMR simplex is always single-slot, unless you have the defective Baofeng model that always transmits on both slots (resulting in it being banned from repeater use).
It's my understanding that DMR simplex typically uses both time slots (unsynchronized - since no sync signal is available). However, the option to use Dual-Capacity, Direct Mode (DCDM - aka double-slot) is offered in some DMR radios.
Nope. DMR simplex is always single slot. The transmitter is only transmitting 50% of the time.

Baofeng is the only exception; their first DMR radio TXed on both time slots, and as a result you couldn't use it on repeaters because it spammed both slots. But that was due to a firmware bug, not correct operation. Only repeaters are supposed to TX on both slots.
 

chief21

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Nope. DMR simplex is always single slot. The transmitter is only transmitting 50% of the time.
I beg to differ. I've read numerous documents and tutorials that state otherwise. Here's an excerpt from NE1B (emphasis is mine)...

  • DMR simplex will go farther. It does not require the repeater handshake. Traditional DMR simplex occupies BOTH timeslots.
  • A new Dual Mode DMR Simplex is now available on Motorola radios.
  • It is very useful in commercial applications where a company has an FCC license for a frequency. Then two different departments can have independent communication on the licensed frequency.
  • Use Talk Group 99, Color Code 1, Time Slot 1 (although for most radios the Time Slot does not apply since simplex occupies both Time Slots)
And here's a cite from RR...

"Dual Capacity Direct Mode (DCDM) is a DMR enhancement that can be employed when using simplex (direct) communication between radios. When operating with a DMR repeater, the repeater provides a sync signal for the two DMR time slots. Normally, DMR simplex operation between radios does not use time slots since there is no sync signal available. DCDM is an added feature that allows one of the radios in a simplex communication to provide a sync signal, thereby allowing the use of both time slots (i.e. Dual Capacity)."

And here is an excerpt from Ailunce/Retevis that shows DMR simplex operation vs. DCDM (two-slot) operation...

1. HD1 DMR Mode is set to Simplex, RT82 DMR Mode is set to Simplex, and set the same color code, contacts, frequency.
Set HD1 time slot: 1

(1) Set RT82 time slot: 1, the two radio can be connected;

(2) Set RT82 time slot: 2, the two radio can be connected;

Set HD1 time slot: 2
(3) Set RT82 time slot: 1, the two radio can be connected;

(4) Set RT82 time slot: 2, the two radio can be connected;

2. HD1 DMR Mode is set to Double slot, RT82 DMR Mode is set to Simplex, and set the same color code, contacts, frequency.
Set HD1 time slot: 1

(1) Set RT82 time slot: 1, the two radio cannot be connected;

(2) Set RT82 time slot: 2, the two radio cannot be connected;

Set HD1 time slot: 2
(3) Set RT82 time slot: 1, the two radio cannot be connected;

(4) Set RT82 time slot: 2, the two radio cannot be connected;

3. HD1 DMR Mode is set to Double slot, RT82 DMR Mode is set to DCDM, and set the same color code, contacts, frequency.
Set HD1 time slot: 1

(1) Set RT82 time slot: 1, the two radio can be connected;

(2) Set RT82 time slot: 2, the two radio cannot be connected;

Set HD1 time slot: 2
(3) Set RT82 time slot: 1, the two radio cannot be connected;

(4) Set RT82 time slot: 2, the two radio can be connected;
 

dazey77

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Chief, he is right, your research is flawed and some of this relates to the TDMA/DCDM. Lots of what you quoted is factually incorrect or badly written. Your fighting your research against people who know you are wrong.
There are also some other inaccuracies in this thread.
In repeater mode DMR transceivers MUST transmit in single slot only (the Baofeng mentioned didnt hence all the issues)
In simplex mode 90% of transceiver transmit in single slot only, providing all the battery life advantages. I believe there were other cheap HTs that did dual slot simplex in the early days.

DCDM has nothing to do with whether a HT transmits in single or dual slot (but requires single slot)

DCDM, according to Motorola is a motorola patented function (note the Hytera court case and that they were forced to remove). DCDM is a way of forcing the transceivers to regard the two time slots as two completely independent channels. This is not part of the main DMR spec. It seems that Motorola cant be bothered to chase the small manufacturers yet. It does include methods for syncing the two streams.

For a simplex radio in a normal DMR mode, the radio will receive calls from either timeslot. The transmitting radio can change which slot it transmits on, there is no need for 'sync' as there is only one data stream. The radios normally lock into whatever slot they hear as active, if there is an irrelevant call comes in on slot 2 then the radio will not hear a relevant call on slot 1 while both are happening. You can even see this in the CPS software, you can always select the slot in simplex.

Hytera Pseudo trunk is hyteras way of achieving two calls in a simplex frequency (but in one logical channel vs the two of DCDM) which works by freeing up the reciever to listen to both slots for a relevant call and by allowing the transmitter to swap between slots based on availability. This also has to sync to existing transmissions. It will easily integrate other manufacturer simplex radios and hop around them in time.

All the bits you quoted around DCDM are about the fact that its splitting it into logical channels, nothing to do with slots transmitted.
 

jonwienke

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Regardless of the documentation, there are various experiments you can perform to see that DMR simplex is pulsed with a 50% duty cycle:

  1. You can also listen to the output of a DMR transmission with an analog radio, and hear it pulsing on and off 16.6 times per second while the signal bars flicker on and off.
  2. You can watch the bandscope display flickering in SDR# or similar programs, and see a corresponding dotted line in the waterfall display, indicating the TX power is cycling on and off. You may need to speed up the scrolling setting on the waterfall display to see the dotted line effect, but it's there.
  3. And you can observe that the power reading with a watt meter that shows average power is 50% of the analog FM reading when you TX in DMR mode.
  4. Uniden's Close Call doesn't pick up the transmission, because Close Call requires a continuous TX for more than 30ms to trigger a hit.
The experimental data is definitive. DMR simplex only actively TXs 50% of the time, and the same goes for client radios talking to a repeater.
 

RRR

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That's one of the advantages of using DMR on a portable, 50% duty cycle = much better battery life!

Now the repeaters, on the other hand, transmit both slots
 

chief21

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OK, guys... Perhaps I've been led down the garden path. You're saying that a DMR radio in simplex receive mode is open to using either slot and locks on to whichever one it finds, but only one slot is actually used.

Got it.

In the case of DCDM, the info from Retevis (which I find hard to dispute since they are a manufacturer) appears to suggest that the time slots can be isolated when operating in that mode, thereby creating two discrete talk paths. I would suppose that this becomes possible by preventing the radio from accepting either time slot (as in DMR simplex) and forcing it to accept only one or the other. How else could that occur using TDMA?

I find this subject very interesting - especially repeater talk-around in DMR mode. As a former member of the fire service, I've always found talk-around to be a valuable tool for close-in communication (while still monitoring a repeater) or as a "fail-safe" mode (if the repeater goes down or is out of range). As far as I've been able to determine, repeater talk-around (in the normal sense) is not possible in DMR due to the time-sync disparity between the repeater output and the same-frequency radio attempting talk-around. Does this sound right? (Feel free to expand on this.)
 

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As far as I've been able to determine, repeater talk-around (in the normal sense) is not possible in DMR due to the time-sync disparity between the repeater output and the same-frequency radio attempting talk-around. Does this sound right?
Nope. With a single-frequency repeater, the settings for the client radios are identical for repeater and direct simplex use. Example:

Handheld: TX on slot 1, RX on either slot, frequency the same for RX and TX.

Repeater: RX on slot 1, TX on slot 2, same frequency for RX and TX.

When a handheld keys up, it tags its broadcast with Slot 1. The repeater syncs with the handheld, and echoes what it hears in the gaps between the handheld's transmissions on the same frequency, but tagged with slot 2.

RXing radios will randomly pick slot 1 or slot 2 to RX if both the direct signal from the TXing handheld and repeater are receivably strong.

If the TX handheld signal is too weak, the RX radios will lock on to the repeater's TX on slot 2.
If the repeater goes down, the RX radios within range will simply RX the slot 1 TX coming directly from the TXing handheld.

So repeater talkaround in this case is not only possible, but seamless and automatic--totally transparent to the user.
 

kayn1n32008

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DCDM is a method for allowing use of both time slots on a simplex channel by using one of the radios on frequency as the timing reference for all.

@jonwienke, the subscribers do not determine slot timing, other than to tell the repeater which slot they are transmitting on, it is the repeater that determines the slot time sync for the subscribers.
 
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chief21

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So repeater talkaround in this case is not only possible, but seamless and automatic--totally transparent to the user.
Hmmm... interesting. Over the past year or so, I've read (and participated) in several related discussions on RR and other forums, and this is the first time I'm hearing this. In addition, I've previously tried to implement TA in conjunction with several DMR repeaters - but never successfully.

Other than setting up a programmable button to activate TA, can you share what other programming parameters are necessary to implement this feature? In your explanation, you say that the repeater is on the same frequency for TX and RX. That, of course, is not typical. If such is possible, how would the repeater know to do that? In any case, would the repeater transpose the voice from slot 1 to slot 2 by default, or does it need to be programmed in that way? What happens if slot 2 of the repeater is active with another user/talkgroup? So many questions.

I realize that these discussions can be difficult in text. Could you point me to a site where there might be a diagram or illustration of how DMR talk-around works?
 
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jonwienke

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@jonwienke, the subscribers do not determine slot timing, the repeater determines the slot time sync for the subscribers.
Not in single-frequency repeater mode. The repeater doesn't transmit until it hears a signal, and it syncs itself with the subscriber TX radio.
 
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kayn1n32008

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@chief21 here are three different subjects in this thread that are being confused.

1: DCDM. Motorola’s method for allowing two talk paths on a simplex frequency.

2: Single frequency repeaters(simplex with the subs transmitting on one slot, and the repeater, repeating slot one onto slot two.

3: Talk around on a repeater output.
 

vagrant

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This is interesting and cool if the AnyTone AT-D578UV III PRO does this single frequency repeater mode. I would like to see this in action, as would prcguy and the point of his original thread.
Nope. With a single-frequency repeater, the settings for the client radios are identical for repeater and direct simplex use. Example:

Handheld: TX on slot 1, RX on either slot, frequency the same for RX and TX.

Repeater: RX on slot 1, TX on slot 2, same frequency for RX and TX.
 

RRR

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My head hurts....

Best way we have gotten close to this is to have programmed simplex freq. with scan (Pri. 1 on simplex,, and had the repeater as "Priority 2")

Of course, you had to change channels to talk on the Repeater, but it was just one channel down
 
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from Hytera's DMR system planner

In Direct mode, the slots on the channel are assigned dynamically. Slot 1 is used by
default. While in Repeater mode, the slots are fixed, and the repeater is used for
transferring the received voice signals and data. Comparatively, in Direct mode, the
subscriber will select the time slot dynamically for transmission. The first used slot
will be taken as Slot 1, and the latter one to be used is considered Slot 2. While in
Repeater mode, Slot 1 and Slot 2 are fixed, but the subscriber, except the one that
has designated the Pseudo Trunk Tx slot, can use any one of them for transmission.
----------------------
A single freq repeater is nothing more than a store and forward system using slot 1 in and slot 2 out.
This video shows how it works on a PD982i.
 

chief21

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@jonwienke While searching for answers about TDMA talk-around, I came across a similar thread that we both participated in nearly three years ago... and I still don't have a definitive answer as to how to implement talk-around in conjunction with a typical, 2-frequency DMR repeater. The search continues.
 
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