MMDVM Duplex TX ok, RX not, but Downlink recognized

Help with DMR issues
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DO8SEB
Posts: 6
Joined: Fri Jul 17, 2020 12:25 pm

MMDVM Duplex TX ok, RX not, but Downlink recognized

Post by DO8SEB »

Hello Community,

i got a mmdvm dual hat with pi-star running. in Simplex-mode i can join Brandmeister network without problems. RX and TX is fine.
whether i change to duplex-mode i have a problem.

the hotspot is joining the BM network and i can hear the talkgroups and OMs. all good.
but if i transmit from my HT the hotspot protokoll says: "Downlink Activate received from DO8SEB" but nothing else. there isn't recieving any network information.

anybody know where is my problem?

TX and RX offset is set right. it works fine in simplex.
i just joined the Brandmeister network, nothing else is aktive (DMR+ is deaktive).
i am joinung dmr 2621_germany. i also tried other gateways, but same issue.
73, Sebastian

Dipl.-Ing.(FH), DO8SEB @ Pi-Star MMDVM with Anytone D578/878.
AF6VN
Posts: 821
Joined: Fri Jul 20, 2018 1:15 am

Re: MMDVM Duplex TX ok, RX not, but Downlink recognized

Post by AF6VN »

"dual hat" is not a sufficient description -- It could apply to a DUAL BAND (can operate on 2m or 70cm, as configured by the user, but only one at a time) or DUPLEX (has two antennas, often has both time slots available).

Duplex mode requires the unit to be programmed with separate Rx and Tx frequencies -- typically using whatever is the normal repeater shift in your area. It also requires the radio to be programmed with both frequencies (radio Tx on board Rx, radio Rx on board Tx). Did you set up the radio channel(s) for such repeater settings.

"Tx and Rx offset" has a different meaning in Pi-Star configuration -- correction factors for boards that are slightly out-of-tune; most DMR radios don't use a repeater shift setting, but require explicit entry of both frequencies.

Showing us the board configuration settings from the control panel, and the channel settings from your radio programming software could be of use.

--
AF6VN
Dennis L Bieber
DO8SEB
Posts: 6
Joined: Fri Jul 17, 2020 12:25 pm

Re: MMDVM Duplex TX ok, RX not, but Downlink recognized

Post by DO8SEB »

sorry for insufficient informations!

i am on a pi zero with a dual hat modem on it connected via gpio, it has 2 antennas.
i have programmed rx and tx frequency diffrent. in the radio codeplug i programmed these frequency inverted for sure.

First Simplex:
whether i program simplex with one frequency, i can rx and tx perfect to BM network. also sms and echo works fine. so i am sure the offset setting from the modem are correct.
modem type: stm32_dvm / mmdvm for pi (gpio)

https://ibb.co/9tGsCq8

now duplex:

Configuration at pistar:
https://ibb.co/zbCgJpp

Configuration radio codeplug:
https://ibb.co/9cD3R6s

in duplex mode i only change the modemtype to: mmdvm_hs_dual_hat for pi (gpio)

with this config i can hear OMs perfekt. i see network is connectet in the tableau and i see OMs whether they send.
but if i am sending, in the protokoll only i see: "downlink activate recieved"

https://ibb.co/gdjTS18

but nothing to see in the tableau, sms wont work, echo wont work.

internet connection is via fritz.box over telekom, all ports are free for the pi-star ip adress.
73, Sebastian

Dipl.-Ing.(FH), DO8SEB @ Pi-Star MMDVM with Anytone D578/878.
AF6VN
Posts: 821
Joined: Fri Jul 20, 2018 1:15 am

Re: MMDVM Duplex TX ok, RX not, but Downlink recognized

Post by AF6VN »

DO8SEB wrote: Sat Oct 03, 2020 2:48 pm Configuration at pistar:
https://ibb.co/zbCgJpp
Off-hand, I'd consider those frequencies are too close together. You've only got a 25kHz separation, and while DMR is supposed to fit in a 12 kHz channel (6kHz per timeslot), you may still have some low sidebands causing interference. That's why I mentioned whatever is normal repeater shift for your region (70cm repeater shift in the US is 5MHz, and even 2m uses 600kHz
in duplex mode i only change the modemtype to: mmdvm_hs_dual_hat for pi (gpio)
That's not enough -- you can probably leave it as that even for simplex, since that identifies the type of board connected.

Did you change the CONTROLLER MODE to *Duplex Repeater?

--
AF6VN
Dennis L Bieber
DO8SEB
Posts: 6
Joined: Fri Jul 17, 2020 12:25 pm

Re: MMDVM Duplex TX ok, RX not, but Downlink recognized

Post by DO8SEB »

Thanks for that fast reply!

You are Right! I will change the frequency and Test it again. Our Shift is normally 7,6mhz. But we have Special reserved frequencies for hotspots. I do change it and answer asap.

Thanks for your thoughts!


edit:
thanks a lot for your tips! all my programming was right, just as you said, die frequency overlap killed it. i now have a maximum shift programmed and it is working fine now! but you have had also right with the modem type. i have to change it to the stm32 one, not the dualhat one.

tanks a lot for your help!

In Germany we say, sonetimes you dont see the Forest out of all the trees:)
73, Sebastian

Dipl.-Ing.(FH), DO8SEB @ Pi-Star MMDVM with Anytone D578/878.
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