Simplex repeater possible?

[KA1CM]

Hi all, this might not be a question about openGD77, it more of a technical question about DMR in general. However, I believe technical people of this forum might have an idea or maybe the explanation on the topic on why it is possible or impossible.

So, if we have a look at simplex DMR. We can have two conversations going on because we have two times slots. Is it possible to have a simplex repeater that TX on one time slot and RX on the other? If it is possible, do we still need carvity filter on the repeater?

Have anyone come up with this idea before? Any documentation and/or experiments about this idea on the internet?

73, KA1CM

[F1RMB]

Hi,

In simplex, you don't have two TS.
What you're looking for is called DCDM (Dual Capacity Direct Mode).

Cheers.
---
Daniel

[G4EML]

Yes, it is called Single Frequency Repeat and is available on high end DMR radios from the likes of Motorola and Hytera. As Daniel says it also needs DCDM support on the handhelds to differentiate the timeslots.

It doesn't need a duplexer as it is single frequency. However it does need radio hardware that is capable of switching between Tx and Rx in the 1ms gap between timeslots. This is not an easy thing to do as making a receiver that can turn on and be at full sensitivity in 1ms is difficult. The alternative of leaving the receiver on all the time also poses problems as it has to cope alternatively with a weak Rx signal and a massive Tx signal.

We have looked at whether it could be done with OpenGD77 but none of the radios are able to switch fast enough.

Colin G4EML

[KA1CM]

Thank you Daniel, Colin,

Based on the keyword “single frequency DMR repeater” I have found some interesting link. I will dive into it.

P.S. how the
youtu.be/bdfbtskJx_M tag works?

[F1RMB]

Thank you Daniel, Colin,

Based on the keyword “single frequency DMR repeater” I have found some interesting link. I will dive into it.

P.S. how the
youtu.be/bdfbtskJx_M tag works?

I fixed it for you. You have to put the video ID only, no http://.... and no parameters '?......'. For this one it's

Code: Select all

[youtube]bdfbtskJx_M[/youtube]

[KA1CM]

Thank you, Daniel.

[KA1CM]

This one said Anytone 578 can also do it, not so sure why he has to set both the 878 in DCDM mode though. And it is weird that both 878 can not hear each other when he turn the 578 off. Both of the 878 are on the same frequency and time slot.

youtu.be/A4VXWvnCGvM

[G4EML]

The reason the two handhelds can't hear each other is because they are both set for DCDM TS Split mode. They transmit on the selected timeslot but receive on the other one. Hence when set to transmit on TS2 they are actually receiving on TS1.

As the guy says this SFR implementation is specific to Anytone. DCDM TS Split mode is something they have created themselves. I don't think it is compatible with other brands of radio.

Colin G4EML