DMR full duplex operation i.e. tx and rx at the same time.

Post Reply
G4EML
Posts: 919
Joined: Sat Nov 16, 2019 10:01 am

Re: DMR full duplex operation i.e. tx and rx at the same time.

Post by G4EML » Thu Sep 15, 2022 5:52 pm

As far as we can tell it appears that only the top end radios support this. The Tx/Rx switching time is critical. It really needs a totally separate receiver and transmitter so that both can be configured and ready to operate almost instantly. The Rx AGC also has to be able to handle massively different signal levels between the two timeslots.

ok1pt
Posts: 167
Joined: Mon Jul 20, 2020 3:38 am

Re: DMR full duplex operation i.e. tx and rx at the same time.

Post by ok1pt » Thu Sep 15, 2022 7:12 pm

G4EML wrote:
Thu Sep 15, 2022 5:52 pm
As far as we can tell it appears that only the top end radios support this. The Tx/Rx switching time is critical. It really needs a totally separate receiver and transmitter so that both can be configured and ready to operate almost instantly. The Rx AGC also has to be able to handle massively different signal levels between the two timeslots.
Hi
Currently, at least two not-so-top-end radios are capable of SFR:
- Anytone AT-D578UV (a mobile radio)
- Radioddity GD-88 (a handy radio).
I own both of them. The Anytone implementation is currently relatively robust, it really works, after about 2 years of development (first implementations suffered from sync problems etc). The Radioddity radio is new, the firmware looks more like in the beta stage (and update is not yet available), a lot of quirks and bugs is present, but it really can be configured and looks like working (but I didn't perform serious tests, I just configured this mode on and keyed up another radio to see, that it shows RX on one channel and TX on the other one.

WIth regads & 73,
Pavel

VK3KYY
Posts: 7481
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: DMR full duplex operation i.e. tx and rx at the same time.

Post by VK3KYY » Thu Sep 15, 2022 9:20 pm

I tried to implement this on the GD77 but as Colin has said, the radio RF chip takes too long to switch between Tx and RX and the beginning of the RX data is lost.

The GD88, which is actually a Kydera radio, rebranded with modified firmware, is 2 complete radios in one housing so would not have the problem of the time taken to switch between Tx and RX probably because they leave the Tx running all the time, but turn off the PA during the RX period

VK3KYY
Posts: 7481
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: DMR full duplex operation i.e. tx and rx at the same time.

Post by VK3KYY » Sat Sep 17, 2022 3:48 am

What do you mean by Cross Band Repeat?

Is the radio acting as the the repeater, transmitting and receiving at the same time ?

ok1pt
Posts: 167
Joined: Mon Jul 20, 2020 3:38 am

Re: DMR full duplex operation i.e. tx and rx at the same time.

Post by ok1pt » Sat Sep 17, 2022 3:53 am

ve7mdt wrote:
Sat Sep 17, 2022 2:50 am

I have the D578UV III but I haven't really used it yet. I didn't even know it can do SFR, I know it can do cross band repeat, in D/A, A/D, D/D, A/A modes.

So how do you set up the user radios (and what radios)? Most radios cannot be program to TX on 1 slot and RX on the other slot. And many radios don't have digital monitor mode for both slots in order to listen to the other slot? So is this limited to only certain user radios to make this work?

Hope you can give a bit more info, as I am very interested in this.

Thanks in advanced.
Hi!
I tested the SFR mode with a pair od AT-D878UVs, one of the basic type and the second with extended memory and bluetooth (PRO version).
Both these models have all the necessary Rx/Tx timeslot setting options to support SFR with 578 in their recent firmware.

Regards,
Pavel

ok1pt
Posts: 167
Joined: Mon Jul 20, 2020 3:38 am

Re: DMR full duplex operation i.e. tx and rx at the same time.

Post by ok1pt » Sat Sep 17, 2022 4:01 am

VK3KYY wrote:
Sat Sep 17, 2022 3:48 am
What do you mean by Cross Band Repeat?

Is the radio acting as the the repeater, transmitting and receiving at the same time ?
Yes, the radio can do this in any mode combination, but one band must be set to VHF and the other to UHF. It operates symetrically, i.e. when somebody transmits on the VHF side, it's repeated to the UHF and vice versa, in any mode (A/D).
73, Pavel OK1PT

VK3KYY
Posts: 7481
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia

Re: DMR full duplex operation i.e. tx and rx at the same time.

Post by VK3KYY » Sat Sep 17, 2022 4:22 am

ok1pt wrote:
Sat Sep 17, 2022 4:01 am
VK3KYY wrote:
Sat Sep 17, 2022 3:48 am
What do you mean by Cross Band Repeat?

Is the radio acting as the the repeater, transmitting and receiving at the same time ?
Yes, the radio can do this in any mode combination, but one band must be set to VHF and the other to UHF. It operates symetrically, i.e. when somebody transmits on the VHF side, it's repeated to the UHF and vice versa, in any mode (A/D).
73, Pavel OK1PT
Cool.

ve2ugo
Posts: 46
Joined: Sat Nov 16, 2019 5:28 pm
Location: Quebec, Canada

Re: DMR full duplex operation i.e. tx and rx at the same time.

Post by ve2ugo » Sat Sep 17, 2022 5:58 am

The 578 can also, for example, listen in DMR on VHF and retransmit in fm on the other band and vice versa. Quite interesting too!

And the SFR (DCDM TS split) is really interesting. Could solve certain problems or difficulties in implementing rptr at a lower cost. Hoping the feature spreads...

Post Reply