DMR Simplex Operations – Single Frequency

The Anytone D878UV, D878IIUV and D578 have the following modes available

I Programmed two Anytone D878’s as follows.

Test 1 Repeater Mode
Radio 1 TS1 Repeater Mode
Radio 2 TS2 Repeater Mode
Radio resets to Simplex Mode if TX and RX frequencies are the same. See Test 2

Test 2 DMO/Simplex Mode
Radio 1 TS1 DMO/Simplex Mode
Radio 2 TS2 DMO/Simplex Mode

Radio 1 TX on TS1, Radio 2 set on TS2 hears and opens receiver and responds on TS2
Radio 2 TX on TS2, Radio 1 set on TS1 hears and opens receiver and responds on TS1
It appears that in DMO/Simplex mode each radio is listening on both Time Slots, and will respond on it’s programmed time slot.

Also the MD398 (Tier1) opens both D878’s regardless of which mode is selected. The MD398 transmits on the same info on both timeslots.

Radio 1 TX on TS 1 – Radio 2 RX on TS 1 Will Not Rx, but will RX when set to TS2but will RX TS 2
In this mode the D878 transmits on one TS and receives on the other.

DCDM Double Slot
Radio 1 TX on TS1 – Radio 2 TS1 Receives OK, Radio 2 set to TS 2 does not Receive.
This mode gives the true isolation between TS1 and TS2

ETSI Specification TS 102 361-1 V2.2.1 (2013-02)

I had a look at the ETSI specification. There is a lot to get your head around but found the following interesting. It appears to me that two frequency and single frequency operations are handled differently.

Some key elements I had to wrap my head around were “Simplex”, “Duplex”, “Single Frequency”, “Two Frequency”, “Direct Mode”, “TDMA” and “Non-TDMA”

My take on what the following charts show, is that a mobile/portable to another mobile/portable or to a hotspot( in single frequency mode) operates on TS2, with TS1 idle

With this in mind it is understandable that my tests of ts1 to ts2 all worked as indicated. Even the Tier 1 radio which I am told transmits on both TS1 and TS2 at the same time passed thru and I am assuming that the TS1 data was dropped by the hotspot.

An additional test. Three radios on single frequency. R1 TX on TS1, R2 TX on TS2, R3 RX on TS1. I keyed up on both R1 and R2 at the same tine, talking into only one at a time and only the audio from R2 on TS2 got through to R3. All tests were done on a single frequency TG99, CC1 All transmissions appeared in the MMDVM log on TS2.

simplex: mode of working by which information can be transferred in both directions but not at the same time. (Can be Single or Two Frequency)

duplex: mode of operation by which information can be transferred in both directions and where the two directions are independent NOTE: Duplex is also known as full duplex. (Can also be Single or Two Frequency)

1:1-mode: 1 traffic channel mode NOTE: 1:1-mode supports one “MS to fixed end” duplex call or one simplex call with an optional inbound RC using a two frequency BS.

2:1-mode: 2 traffic channel mode NOTE: 2:1-mode supports two independent calls which may be either “MS to fixed end” duplex calls, simplex calls using a two frequency BS or simplex calls between MS units on a single frequency.

BS: Base Station / Repeater (Also Duplex Hotspot in Two Frequency Mode)
MS: Mobile/Portable Station (Also Simplex Hotpot in Single Frequency Mode)

My tests show that two channels are NOT available between MS units on a single frequency and the charts below indicate the same. See chart 5.16 and 5.20 below.

A pi-star hotspot on a single frequency set to simplex mode responds in the same fashion.

The DMRGateway in simplex mode on a single frequency will also not work on TS1. When attempts are made to convert from TS1 to TS2 or TS2 to TS1, the result will always come out on TS2. This conversion can only be done on a duplex hotspot in two frequency mode.

Direct Mode- The ONLY Mode used By Tier 1 Mobile (TYT MD 398)

DMR Gateway

This rule
TGRewrite1=1,4000001,1,1,999999 will actually go through the MMDVMHost as TS2 and that will show up in the MMDVMHost log file as such.

just for giggles I changed my rules for TGIF as follows. I changed all the TS2’s to TS1 just for this exercise


I use the DMRGateway differently than most in that I use what I refer to as the 8 Digit mode
The first line handles all normal traffic on Network 4 – TGIF
The second line handles all the new 7 digit talk groups on TGIF
The last line takes all incoming private calls and feeds them directly to the radio.

Sorry!! I also use my own version of the DMRGateway that locks the gateway to only one network at  time so the
TGRewrite1=1,1000001,1,1000001,5599999 rule can be used in all networks. The 14 locks the gateway into Net 4 only.
Th only difference is the addition of the locking filters, all routing remains the same.

Now when I transmit on 1403023 TS1 The MMDVMHost log shows me on TS2

M: 2023-10-19 15:56:08.550 DMR Slot 2, received RF voice header from VE3RD to TG 14003023
M: 2023-10-19 15:56:08.960 DMR Slot 2, received RF end of voice transmission from VE3RD to TG 14003023, 0.4 seconds, BER: 0.4%, RSSI: -47/-47/-47 dBm
and the dmrgateway log shows me on ts2 as well
RF transmission: Net=4, Slot=2 Src=3023954 Dst=TG14003023

However these packets do not get to the TGIF Server

Changing the Rules to

This has exactly the same effect and no response from the TGIF Server

Now changing radio back to TS2 and the rule set  to
Both logs show this on TS2 and the packets make it to TGIF on TS2, Across the Bridge to DMR+ on TS2 and across to BM

Now putting it all back to normal

This has exactly the same effect as the previous rule set
Bottom Line, the use of TS1 in a simplex hotspot in the DMRGateway does Not perform as expected and in some cases is redundant.