Monday, April 16, 2018

UserGuide for MMDVM Repeater Kit Board (LinkerV3)

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.

Has verifying radio list ,
by Nano & BI7JTA SPOT users:
@BG8FCQ GM950i, setting view the end of this BLOG
@BD7NJC M120  ,same as GM300,
@BD7ILU GM300 , Can not change TCXO,otherwiseTX )to termail radio not work
@BH3PXX GM300 DR-1X FT-7800 C4FM DMR
@BH1RQN GM338 ,need change pi-star config TXInvert=0
@DW4CHZ maxtrac motorola ,two radio are working good without any adjustment on board
@BI7JTA CDM1250/CDM1550/GM338 need to do:
1) Re program radio follow user guide,  
2) Change pi-star config TXInvert=0
@Mr. Khairul Malaysia: Writw MATCOMS (Malaysia) GM338 , need change pi-star config TXInvert=0 and RXInvert=1
@DW7FCV  ICOM ID-4100 DStar bandwidth to narrow 12.5KHz
@IW6BFE MTR2000 add 22uF capacitor to TX line
@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
@Huawei 450 work in P25 mode, other not feedback,
@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.


Recommend radios for homebrew repeaters (G4KLX)

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.

Linker V3 define↓

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↓

Simplex mode(RX and TX in one board) V2↓

Repeater(Duplex) mode (RX and TX split into 2 board) V2

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,

Some link for reference,

By f5uii

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

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