Usually i do not post links to foreign content but here is a really interesting talk by Bruce K6BP on the state of digital voice and open source usage within amateur radio in general.
Thanks a lot to Hamradio Now for making this talk available !
I have a Tytera MD380 DMR transceiver now. Flashed latest MD380tools and database yesterday and hope to make a first qso soon. A mmdvm hotspot is in the pipeline but i still need to connect a transceiver.
TYT MD380 DMR radio
Triggered by some forum discussion about interference risk of operating repeaters in neighbor channels in 6.125kHz channels I was curious about the TX spectrum of my IC-E92. The measurement was done radiated. I checked for neighbor channel interference. You can see the delta values bottom right.
IC-E92 FM wide 1750Hz
IC-E92 FM narrow 1750Hz
D-Star (only half span screenshot):
You can see that D-Star is really the most narrow band mode. Using neighbor frequencies at close QTH still cannot be suggested but at least the interference will be less than for narrow band FM.
Since a long time David Rowe VK5DGR works on a open-source low-rate voice codec. This project is called codec2.
Now a variant of this codec is used in a amateur radio digital voice mode that was evolved out of the well known FDMDV software.
The mode uses OFDM with 14 carriers DQPSK and 2 pilot carriers with twice the power modulated in DBPSK.
The bandwith is 1kHz, so 2 of the signals would fit to 1 SSB channel. The datarate of the voice is 1375 Bit/s + some data bits for callsign information etc.
Its intended that in the end this mode can also be used for DX connections. Lets see what live tests will bring. On 20m obviously the frequency 14.236MHz is used as center of gravity.
For using the mode you would need either a two-soundcard PC (one for connecting a headset and one for creating the digital modulation signal) or a SDR setup with virtual soundcards. Currently a windows beta release can be downloaded as binary. For Linux you have to download the source and compile it on your own. David created a nice Makefile that downloads and compiles all dependecies.
You find further information on the project page http://freedv.org/tiki-index.php.
Also some videos are linked that show the operation and the audio quality of this digital mode.
some experiments with FreeDV and Quisk
How the digital signal of Freedv/FDMDV2 sounds like:
How the decoded audio sounds like (its only 1375bit/s with 1kHz bandwidth!):
There is now a reflector group for V/U/SHF sked alignment especially during contest operation.
You find this on DCS001 reflector module U. Thanks to DG1HT !
I will be qrv in this module during July V/U/SHF contest from JO60LK.
This week i got the new DVRPTR pcb. (see www.dvrptr.de)
Connected to a Windows or Linux PC it is easy to create a hotspot for connecting to D-Star Reflectors ans X-Reflectors. From time to time i am running a hotspot on 430.225MHz from my home location in the east of Dresden (Just when i am at home). Probably someone can hear it. It is usually connected to XRF010B.
There is a new yahoo group (in german language) that is about the digital voice modem (DVMODEM) for the Siemens C5. This modem was created by DO1FJN, Jan.