OpenGD77

Hello .
I have baofang 1801 with lasted opengd1801 firmware
Firmware is very good , but i have a problem with simplex in dmr . When I broadcast, they don't hear me and I hear them perfectly.
I have one contact with same color code and same time slot with same frequency.
in fm everythink is perfect.
If i upload original firmware , communication is ok two direction. but if i flash with OpenDM firmware (first choise 3.4.6.sql and after this OpenDM_1801.bin) flash is successful and dmr is ok but nobady can hear me in simplex.
i dont have a local dmr repiter to test dmr connection.
any idea ?
thank you


LZ1GAD

lz1gad wrote: ↑

Wed Dec 08, 2021 7:28 am

Hello .
I have baofang 1801 with lasted opengd1801 firmware
Firmware is very good , but i have a problem with simplex in dmr . When I broadcast, they don't hear me and I hear them perfectly.
I have one contact with same color code and same time slot with same frequency.
in fm everythink is perfect.
If i upload original firmware , communication is ok two direction. but if i flash with OpenDM firmware (first choise 3.4.6.sql and after this OpenDM_1801.bin) flash is successful and dmr is ok but nobady can hear me in simplex.
i dont have a local dmr repiter to test dmr connection.
any idea ?
thank you


LZ1GAD

I never heard of this sort of problem with simplex

Are the other stations operating in dual capacity direct mode (DCDM) which allows two timeslots on the same frequency?

If they are then they may not hear your transmissions. The open GD77 firmware only supports basic direct mode which only allows one transmission per frequency. The sync words used are different and other radios may only receive one type.

Open GD77 will receive both types of transmission.

If You are hearing the other stations then your colour code and receive frequency must be correct, check you do not have an offset in the transmit frequency. Also make sure you have the correct group call talkgroup selected and not a private call ID.


Colin.

That was really the problem. Thank you very much . After removing the dual capacity direct mode (DCDM) option on the other radio, we heard each other perfectly

thankss

73 from Bulgaria

G4EML wrote: ↑

Wed Dec 08, 2021 10:43 am

Are the other stations operating in dual capacity direct mode (DCDM) which allows two timeslots on the same frequency?

If they are then they may not hear your transmissions. The open GD77 firmware only supports basic direct mode which only allows one transmission per frequency. The sync words used are different and other radios may only receive one type.

Open GD77 will receive both types of transmission.

If You are hearing the other stations then your colour code and receive frequency must be correct, check you do not have an offset in the transmit frequency. Also make sure you have the correct group call talkgroup selected and not a private call ID.


Colin.

Thanks Colin

I've never heard of any other Hams using DCDM

VK3KYY wrote: ↑

Wed Dec 08, 2021 11:44 pm

I've never heard of any other Hams using DCDM

Stock GD77 can do DCDM right? Or maybe it was the MD380. I know one of them could. Never used it, however.

Yes, the stock firmware can do DCDM. However, like a lot of things, there is no documentation for the DMR chip on how to implement this.

It's also very time consuming to reverse engineer and implement features not generally used by Amateur Radio operators
These sort of features literally take hundreds of hours of people's spare time to get working, so unless one of the developers has a personal interest or need in this sort of feature, it's never going to get implemented.

AFIK.
DCDM is used by commercial users who have to license and pay for individial frequencies

For Amateur Radio, I can't think of a use-case where you would need to have 2 simplex transmissions on the same frequency.

VK3KYY wrote: ↑

Thu Dec 09, 2021 11:48 pm

It's also very time consuming to reverse engineer and implement features not generally used by Amateur Radio operators
These sort of features literally take hundreds of hours of people's spare time to get working, so unless one of the developers has a personal interest or need in this sort of feature, it's never going to get implemented.

AFIK.
DCDM is used by commercial users who have to license and pay for individial frequencies

For Amateur Radio, I can't think of a use-case where you would need to have 2 simplex transmissions on the same frequency.

I believe that I know such use-case: SFR (Single Frequency Repeater).
There are countries, like Czech Republic, where duplex HAM frequencies (for repeaters) have to be specially requested from national HAM regulatory organization, and they have to be paid for on the periodical basis. Unfortunately, this must be done even for 50mW duplex hotspots, so most Czech hams use hotspots in the simplex mode, even if they have duplex hardware on their hotspots.
As hams always experimented on the "bleeding edge" of the technology - starting with arc and then tube transmitters, I believe this is still one of the important aspect of the ham interests and even today there is a space to experiment. For example, Anytone AT-D578UV radio, which is very HAM-friendly and isn't extremely expensive like various *OLA or *ERA radios, has the ability to serve as the SFR. It would be very exciting to check this functionality. and I believe that it requires DCDM-capable "clients". In the latest firmware for AT-D878UV, they added the "split timeslot" function to DCDM setting, allowing radio to transmit on one TS and receive on the other, as something to improve the SFR operation with AT-D578 as the repeater. It would be extremely interesting to be able to participate with OpenGD-77 radios on this experiment, and whats important, according to current ham rules in our country, it would be perfectly LEGAL to operate SFR without any extra fees or administrative works, even with high power.
*** HOWEVER ***, I fully understand, that it's probably just a dream and that in current conditions it's extremely hardly doable or, even more probably, undoable. So, I'm not asking to do it, I just replied with one of the possible use-cases for DCDM on OpenGD-77.
With regards, Pavel

I already tried to implement SFR but it did not work, because the RF chip can't change from Tx to Rx fast enough.

The beginning of the Rx TS was lost, which causes the AMBE audio sound strange.