Digital Voice..


Codec2 11/12/2012

Codec2 is the latest thing in Digital Voice for Amateur use, it is an open source voice codec and performs very well at low bitrates.

FreeDV software is now available for windows or linux. Bandwidth is 1100Hz and audio is 1400bps - Just like FDMDV but a little better voice quality in my opinion than the speex codec...

I'm currently looking for skeds on 20m or local 2m to test it out....

Website is here: http://www.freedv.org



D-Star 2010

i have not tried using D-Star yet on the bands and it seems to be getting more popular with quite a few repeaters popping up just to the south of me (just out of normal range!) but there are no repeaters or any stations that i know about that have the capabiltiy of D-Star in the teeside area, including me!

I have found and interesting group that is starting to make an alternative to using a D-Star radio by using some software on the PC to make it possible to receive and transmit D-Star signals using a standard radio and a USB encoder board (dvdongle)

Check out this YahooGroup for more info.


DV Adaptor for D-Star 2009

Just recently i found a cheaper way of doing D-Star Digital Voice..

It's a design using the readily available UT-118 D-Star module for Icom radio's with a home-brew interface board to use with the PC or simple display. The UT-118 modules have been available on ebay for ~£100 new, i ordered mine and it arrived in 5 days from Taiwan!!

It's much cheaper than a new radio and the module from the usual suppliers!

This is the design i have used: http://d-star.dyndns.org/rig.html.en


Over the last week or so i have made up a PCB and fitted the DV Adaptor to my Yaesu FT-480R radio and have made my first d-Star contact!

Here is a photo of the finshed D-Star Adaptor.





I found it very difficulto to find any of the P8 series 30-way connectors the same as the UT-118 so i bought replacement 0.8mm 30-way connectors from Farnell for the UT-118

So far i have made a few changes to the cct drawing on the site to make my adaptor work:

1. Fit 4.7K pullup to pin18 of UT-118 module (without this my adaptor would not transmit)

2. Change R18 and C21 on the audio amp to 470R, 100nF for lower cutoff, you get lots of strange chirps and tweets form the speaker otherwise!

3. Audio output had to be connected to Digital Ground rather than Analogue ground as it was causing distortion to the received data via the Analogue ground path.

4. Fit a pot on the GMSK data output to make it easier to setup radio deviation.

I have modified the drawing as shown on the website with mu modifications Modified DV Adaptor Circuit drawing



Basic version Circuit is in the original DVAdaptor design.

Circuit for LCD version: Here


Here is a recording made the other day from GB7YD before the mods were made to the audio amp.






Here are a few Screen grabs of data from GB3YD 100km away in Barnsley using dstar.exe decoder and my Icom 706 with 9600 packet output into the soundcard on my pc.

if you use this software and the dvdongle you can hear the audio too i believe..

Click to enlarge..







Digital Voice unitl recently has only been on the HF bands in commercial form. Now there is some software whcih can encode your audio into data and then transmit it out on your HF tranceiver with very little effort.

This has all come around due to the software being available for the DRM system that is being used by some of the broadcast stations now. the format of the transmission is the same as that for the DRM transmissions apart from some minor changes like bandwidth and number of carriers. The Dream software is capable of making perfect DRM transmissions of 10 and 20KHz datachannels and works extremely well, the digital Voice software is just a modified version of Dream, called HamDream! this was modified by Cesco HB9TLK (Great work Cesco!) there is also another program for digital voice and that is called WinDRM, this very simple to use.


How it works:

When transmitting the software takes the audio in from your PC microphone and feeds it into the software encoder, the digitally encoded audio is sent to the soundcard output then fed into the HF set's microphone or DATA input socket just like any other digital mode. For receiving all you need is the HF set's receive audio connected up to the line in on your soundcard and the software will decode any strong enough digital voice signals, and you will hear voices from your PC speakers! Great!

The software really requires two soundcards but it can be done with one and the use of the mixer control built into the software to switch inputs/outputs etc..



HB9TLK Creator of WinDRM Software

N1SU Site WinDRM / DRMDV / FDMDV user guide and Download

The WinDRM software looks like this:





Here are some audio samples of the stations i have worked on Digital voice..


In the Beginning 2004 (with LPC or SPEEX codecs)

HB9TLK - Cesco

K0PFX - Mel

OH2GAX - Otso

N1SU - Jason


Received with the new MELP Codec in WinDRM. (Nov 2005)

OE8HWK - Hans

OE3GBB - Gerhard



Early 2007 a new version of the WinDRM software, DRMDV.

DRMDV has been released for use now and decodes signals down to ~6dB SNR compared with the 9-10dB previously. The software just requires the same hardware as WinDRM but is designed specificly for Voice transmission.

It looks something like this!



Late 2007 another version of Digital voice transmitting software is avalable, FDMDV.

This si another attempt at digital voice and seems to work even better. I'm not sure on teh required SNR for it to decode but it starts as much lower strength than DRMDV.

I have tested this mode with Eddie G0EHV on 23cm SSB over ~45KM path and the audio decode was reasonable with a litle breakup, DRMDV would not decode anything when we tried afterwards!

The new software looks like this:




Updated 24th Feb 2008