On 7/21/2022 1:28 PM, DigitalRadioGuy wrote:
I have a bunch of Kenwood commercial radios I was thinking of trying one of them.
None of the radios have any kind of flow control I can see, so, I
was wondering how file transfers worked without losing part of a file due to
buffer over runs. The function reference manuals say the max radio
buffer size is 1K, at least for the one NXDN radio.
I want to try this, but as of yet have not had time.
From what I understand, D-Star radios use the same GMSK digital encoding at the base level as other radios.
What D-Star does is have their own data frame format that is used.
To decode audio, you need the special chip.
So for d-rats, theoretically, for hardware, you just need a GMSK modem like for 9600 baud packet.
You also need to have software send the packet formats that d-star radios accept.
A Zumm Radio MMDVM can handle the GMSK modem part, and while it is designed to be plugged into a Raspberry PI, you can connect up a USB to serial module, or a TTL to RS-232 module and use any computer you want to use. I got one from the Dayton Hamvention to play with.
The same interface is probably used with other GMSK modems that target Arduinos, etc.
Again, I understand that there is software on the Raspberry PI, that knows how to talk to D-Star radios. Using that instead of rolling my own would be a big time saver.
Unfortunately, getting another Raspberry Pi to play with is going to take a while, as they will likely be sold out into 2023.
I was looking to see if a PI-zero could handle the job, so that I did not have to tie up my test Pi system.
And I do not know how hard it will be to have d-rats running on a Pi to communicate with the software that converts the data to d-star packets.
To have d-rats communicate directly with a GMSK modem, we should just need to port the code that communicates with the MMDVM UART to what ever platform that we are running d-rats on, possibly implementing that protocol in Python.
Again, I have not tried any of this yet, so the may be things that I am missing.
Unfortunately there is also a lack of documentation on how the MMDVM API works, when I ask, I just get pointed at the software projects that use it. So apparently reverse engineering the existing software is the only way to use these modems with out a Pi or the Ardunio they are targeting.
What I know so far is that it has some data signals on unknown pins and uses a standard UART for actual data transfer.
73,
-John
