I've bought a MMDVM HS DUAL HAT from eBay. I can config it to run in simplex mode. However, I have problem in duplex mode. I'm using DMR Gateway with RT3S (OpenGD77).
The radio can't find the hotspot in duplex mode and will say "timeout" on the screen, just as when I tried to key up a repeater that is out of range. I don't know how to make it work, please help.
G8SEZ wrote: ↑Wed Jan 10, 2024 5:13 pm
Good, although I would expect both Rx and Tx to have the same offset given there is one TCXO.
Thank you, G8SEZ. I'm encounter another problem. the sensitivity of the hotspot is horrible. with my simplex hotspot, I can use 50mw on my radio where ever in my house. With this duplex, I have to crank up my radio to 1W just to be able to communicate 5 feet away.
Found this on a page re this hat, not sure if you have seen any of it or attempted it....
Detail
Setting For Pi-star software and raspberry hardware (rpi 0-3) new pi4b need remove Right Socket
Pi-star General Configuration for MMDVM_DUPLEX
Set Controller Mode:Duplex Repeater or Simple
Radio Frequency : Freq:144-148,219-225,(Main Band)420-475,842-950
Duplex Mode:Example:RX:438.000000 TX:433.000000
Duplex Mode:Example:RX:145.000000 TX:433.000000
Simple Mode:Example:RX:438.000000 TX:438.000000
Radio/Modem Type:STM32-DVM/MMDVM_HS-Raspberry pi Hat(GPIO) or any other (GPIO board)
option:(don't need now, some old board need set)
Admin->Expert->Edit MMDVMHOST->RXOFFSET=0 TXOFFSET=0 (default value in pistar)
(update:2019/2 new 3225 TCXO so offset is 0 )
update new FW: (pi-star / expert / ssh access / user :pi-star pass:raspberry)
sudo pistar-mmdvmhshatflash hs_dual_hat
The default bit error rate is less than 5%, and the default offset is 0. If the bit error rate is more than 5%, as long as the signal can be received, it can be corrected by offset.
That is a description in the eBay page where I bought it. I’ve done everything according to the instructions on that page, but the performance of the modem in duplex mode is still unacceptable.
You probably need to separate the Rx and Tx antennas by some distance, the Tx wideband noise level is probably high enough to affect the receiver so you either need a diplexer with good filtering and use a fairly wide frequency split or you need to move the antennas at least a metre apart with good quality coax.
Ah, they're PCB antennas, so you need to fit the connectors and disconnect the PCB antennas, they share a ground plane so isolation is going to be very poor.
G8SEZ,
Sounds like a big project, I’m sure I’ve just done something wrong. There is no way this thing is not working. I believe there are tons of this hat out there working.
