Monday, April 16, 2018

Configure Guide for MMDVM Repeater Kit Board (LinkerV3)

Update 2019-12-01,
I continue update in my Wiki website ,now have completed:
for DR-1X
for GM338-CDM1250-CDM1550-CDM750

Repeater Kit Board interface definition (for Nano series) #MMDVM#, using with MOTO GM338/GM300/M120/GM3188, Interface definition reference, other devices follow board interface "PTT/TX/GND/RSSI/COR/RX" .
Compared with Duplex hotSPOT, it can provide larger and more stable power output without the need of TX amplifier.

Some experiences sharing ,
1, @BG8FCQ GM950i, setting view the end of this BLOG
2, @BD7NJC M120  ,same as GM300 ,keep Pi-Star setting default,
3, @BD7ILU GM300 , Can not change TCXO,otherwiseTX )to termail radio not work
4, @BH3PXX GM300 DR-1X FT-7800 C4FM DMR
5, @BH1RQN GM338 , TXInvert=0 RXInvert=0
6, @DW4CHZ maxtrac motorola ,two radio are working good without any adjustment on board
7, @BI7JTA CDM1250/CDM1550/GM338 need to do:
1) Re program radio follow user guide,  
2) Change pi-star config TXInvert=0
8, @F4HES GM340 TXInvert=0
9, @DW7FCV  ICOM ID-4100 DStar bandwidth to narrow 12.5KHz
10, @IW6BFE MTR2000 add 22uF capacitor to TX, view the end part of this blog
11, @BX5AAU Motorola XPR-4550,DMR mode, RX work,BER less 1%; TX work AnyTone decode ok, Motorola terminal DMR radio can not decode. continue trace, video
12, @Huawei450 work in P25 mode, other not feedback,
13, @BI7JTA @BH7JTB FT-7900R, set 9600bps, keep Pi-Star and mobile station default, work DMR AnyTone,TYT-MD2017, not decode in TYT-380G, still trace this problem.
14, @BG6THE Tait t800 repeater TXInvert=1(1:Simplex 0:Duplex) RXInvert=1
15, @BX3ACB FT-818 PKT 9600bps(Not FM),SIMPLEX TXInvert/RXInvert=0,AnyTone-D868/FT-2D RX/TX OK, TYT-MD760 RX OK, TX still testing.
16 @BI7JTA GM3188 Let RSSI open(White Color wire),otherwise can not connect Modem.
17, @BI7JTA GM300 VHF work ,TXInvert=1 RXInvert=1 (UHF RXInvert=0
18, @BG6THE HUAWEI E403-50B SIMPLEX/DUPLEX work perfect, need more operation change inner Circuit
19,@BA5DA, IC-2720 TXINVERT=0 RXInvert=0
20,@Individual cases GM338 TXInvert=0 RXInvert=1 [Thailand HAM]
21,@BG3NCT GM338 use GM338TUNER tool, change 12.5KHz to 25KHz
22,@BI7JTA CDM750 TXINVERT=1 RXInvert=0, keep default.
23,@CA6JAU Motorola PRO3100 ,view the end part of this blog
24,@PY2LY Motorola Pro 5000 view the end part of this blog
25 @BI7JTA Motorola XPR4550 RX work, TX not work;
26 @KE8FJW Motorola CM200 2019-12-16: 
Recommend changing the RF hangtime in the pi-star software from 20 to 1. This will allow a much needed break for the tx radio to cool down.  Very important

Motorola GM3688 RX/TX work.


Recommend radios for homebrew repeaters (G4KLX)

V3F446 from 2019.6

DB9 cable to Motorola radio
Step by step:
1) Test simplex first, use 1x radio, when 2x radio can work well in simplex mode, then
2) test duplex with 2 radio + duplexer .
Otherwise, you do not know where is the problem.
Important: If your external radio have frequency offset, fix first, for my experience, more of the board allow <1KHz offset, but less of them just allow very little offset.
How to fix offset?
1, fix your external radio, (Recommend)
2, make the same offset in your digital radio,

Linker V3 define↓

Pi-Star setting

Radio/Modem Type

Controller Mode: SIMPLEX for one radio, Duplex/repeater for two radio

Linker for Motorola radio(Also for other radio)

FT-7900R, PS/2 Data cable

XPR 4550

Act as a simplex hotSPOT

Act as a repeater(Duplex) mode

POCSAG mode support

MOTO GM300 need modify the P551 to A, P601 to B, open the case,

And keep the TCXO factory ,not change it ,otherwise the TX(gm300 to DMR radio can not decode data)↓

The right radio TCXO has been change, will cause terminal radio can not decode digital voice data↓

                                             Linker V3 define↓

For FT-2720

Test successful with CDM1250(GM338)


GM3188 (Change to Engilsh description soon)

Debug RX:(Terminal radio to MMDVM decode)
Adjust your external repeater radio with your MMDVM repeater board
See the photo and the short videos at the end segment.

1) Test simplex first, use 1x radio, when 2x radio can work well in simplex mode, then
2) test duplex with 2 radio + duplexer .
Otherwise, you do not know where is the problem.

Debug TX:(MMDVM to Terminal radio decode)
Adjust TX ,Radio transmit, terminal device decode if normal.
No, just when your terminal radio not decode digital signal.

SDR spectrum assistant adjustment(Optional) 

Use with POCSAG, firmware RPT_1.4.7

Display interface definition:

OLED: VCC/GND/SCL/SDA (left to right)
Nextion: the STM32F105 not support modem type, just support ttyUSBX,use USB to TTL Adapter,suggest use CP2102 or CH340,
HS RXD to Nextion TX
HS TXD to Nextion RX
HS 5V   to Nextion 5V
HS GND to Nextion GND


Verification by DW7FCV
My ICOM ID-4100 DStar has trouble receiving the TX of the MMDVM node.  Keeps on shifting from DV to FM with no audio.  No issue on RX of the node, I can hear myself on the other hotspots.  Saw a similar issue with the DVMEGA, is the problem from the board or the motorola radio?

ID4100 cannot RX but can TX. My Kenwood THD74 can RXand TX

Put the bandwidth to narrow 12.5KHz. Everything is working fine.
Another update. Narrow bandwidth 12.5KHz works perfectly fine with the ID4100 but now cannot Rx my FTM100D on DN Tx.
Same with DMR, so apparently, MMDVM node simplex is narrow on DSTAR (specifically ID4100) and wide on DMR and C4FM


Extended reading 

Add whitelist Talkgroup to TS1,TS2 #DMR

How to buy

email to

How to flash Pi-Star OS

Download the new version Pi-Star IMG

Add whitelist Talkgroup to TS1,TS2 #DMR

sudo nano /etc/mmdvmhost
# Prefixes=234,235
# Slot1TGWhiteList=
# Slot2TGWhiteList=  

Youtube test Video for reference

Useful resource reference

Connecting BI7JTA MMDVM Repeater board to Motorola GM 340

Ajuste de desviación en frecuencia en MMDVM, parte 1 (teoría) 

Ajuste de desviación en frecuencia en MMDVM, parte 2 (práctica) 

Recommend for Motorola radio 


Collection for radio setting

Programming radio

Config Pi-Star in Expert mode

 Simplex mode

Duplex(repeater) mode

GPIO Definition And Interface Diagram

More Cases:
@IW6BFE Motorola MTR2000 

@CA6JAU Implementación rápida de MMDVM con Motorola PRO3100

@PY2LY Motorola Pro 5000


  1. This comment has been removed by the author.

  2. Good morning, I have recieved one of your repeater kits and everything is working great, apart from one thing.

    When I am receiving a transmission I am not getting an RSSI report, regardless of how strong the signal is I just get S1 / -141dBm.

    Is there something wrong with my setup?

    I am using Motorola GM 300 series radios.

  3. Hello. My name is Kevin and I am attempting to set up a dmr repeater using your mmdvm repeater kit board and a kenwood TKR-850. I am having problems with the transmit drive level. Even with the TX pot full open and levels set to %100 in mmdvmcal, I cannot get enough drive to suppress the carrier. Do you have any recommendations?

    1. I set up a TKR-850 in analog and digital dual mode. Digital is set for DMR and P25. Had a lot of trouble getting TX to work with the same problems you describe - all was fixed when I did a full alignment on the repeater in wideband mode per the kenwood service manual and using a service monitor.

  4. I have exactly the same issue as Kevin. Any ideas?

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