DMR Simplex appears to be working on the MD380, here's how

[kc8lin]

The original Ken code plug did not have any provisions for simplex on a repeater output (talkaround) or on regular simplex. It appears programming simplex is not too complex, but its not as simple as pushing the T/A button on the radio. My radio has the button above the PTT set to select T/A or High and Low power.

What I did was create a new channel under "Channels Information" with the following information.
Channel Mode :Digital
Bandwidth: 12.5Khz
Scan List: None
Squelch: Normal
RX Ref Frequency: Low
TX Ref Frequency: Low
TOT: 60s
TOT Rekey Delay: 0
Power: High
Channel Name: AU Simplex
RX: 443.1125
TX: 443.1125
Admit Criteria: Always

Check Allow Talk around, nothing else checked.

Emergency system: None
Contact Name: Simplex        (this is defined in Digital RX Group List as 99)
Group List: AU Local             (I have Local2, Local9 and Simplex in this Group list)
Color Code: 1
Repeater Slot: 2
Privacy None
GPS System: None

When I select Zone AU Local I have three channels now. One for Local2, Local9 and AU Simplex.     When I select AU Simplex and I put my TRX-2 DMR scanner on 443.1125Mhz I hear audio!  It appears to work well.  I do not have any other DMR Transceiver to test, but it works with a MD-380 and a scanner.

What I am doing is creating a simplex channel for every DMR repeater I have. I am just using the output frequency of the repeater (TX and RX frequency are set the same).  That way if we are at a hamfest we can just switch to simplex on the output.

DMR recommended simplex calling is 441.0Mhz. I have added the Contact Name: Simplex to my simplex channel info as well.

I am not sure what Time Slot simplex uses. I would assume the radio uses the selected time slot (usually 2 for local). The radio however is not full duplex, even though it is only transmitting 50% of the time, the receiver is not active the other 50% of the time. This means it may only transmit on TS2, but it wont be able to simultaneously monitor TS1. 

Another note,
If you are monitoring a repeater and you decide you want to talk DMR simplex on the output, if you just select T/A on the radio it won't do anything. The radio will show a new icon on the display showing you are on Talk Around (T/A), but you wont be able to monitor any Time Slot1 or TS2 radio traffic.  This is an error in the MD-380 firmware. I have been told Motorola radios do not have this bug. If you select TA while monitoring a repeater on the proper slot and color code, received audio will still be heard.

-
Jason Stroll
KC8LIN

[kc8lin]

A quick correction.
  For DMR simplex frequencies like 441.0Mhz, 446.500Mhz, 446.075Mhz, 433.45Mhz the convention is to make Color Code1, Repeater slot1, Group List "Group99" .     



Jason S.

[Bill Mayhew]

In the codeplug file I got from Ken about a week ago, somebody already set up a contact called simplex and added the contact to TG99.  There is also a zone called simplex and channels set up for 446.075 and a handful of other freqs.  The channel defs were set up for tg99, cc1 and admit all.  Simplex is Teir 1, so I believe no time slot is defined.  I am not sure if talkaround tries to emulate actual repeater output and thus a time slot assignment.  I ran into cryptic comment on a DMR forum written in 2015 saying that few, if any, Chinese hand helds implement talkaround correctly.

The MD-380 does transmit something on the channels mentioned above, but I don't have any means to tell if there is any actual payload content since I have only one DMR radio of my own.  I did try briefly tansmitting to Rick's radio on 446.075, and Rick did not appear to be getting any audio output.

I talked to Ken Tuesday evening  on AU Local 9, and Ken said that he and Rick worked out digital simplex operation and Ken would explain it later.

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[KA8OAD]

Hi Jason,

     According to the DMR-MARC association simplex is to be set for TS1 and CC1 always. Also they "strongly suggest" only using the 4 UHF Simplex frequencies that are defined and not using T/A on the repeater frequencies to keep from possibly interfering with any repeater on that frequency.

The value that is most important is setting the Contact to "Simplex" (TG 99) if the TG is set to "NONE", which is what I had my original simplex channels set to, the radio will not transmit audio because it doesn't have a TG to use. Also make sure you have "Admit Criteria" set to "Always" in your channel, for normal repeater operation this value should be set to "Channel Free".

Ken

On Thursday, December 22, 2016 at 3:07:05 PM UTC-5, kc8lin wrote: