During experiments with digital voice mode in hamradio I discovered a nice project describing an adapter for D-Star, DMR and other digital modes based on an Arduino Due and a little PCB to be put on top. This unit is called the Multimode Digital Voice Modem or MMDVM (see ). It seems that this is getting quite popular because hard- and software is Open Source.
The units can be ordered from Bruce, VE2GZI for a very reasonable price. As of writing this the time for delivery was about 3 to 4 weeks. Because this unit was really of interest I decided to build one myself besides having ordered a set of the nice PCBs with SMD parts.
The schematics and some documentation can be found in the correspronding Yahoo Group under . I built the version 1 circuit which currently also delivered if you order one of the PCBs. Alexander, DC5AJ was so kind as to provide me with a prefilled shopping cart from a Germany electronics supplier which I modified slightly. If you want to order the parts, see . All together with a PCB and a cable this is around 18 €. The additionally needed Arduino Due was clicked on eBay for some 15 € – of course a clone and not the original one :).
So that makes just around 30 € for a neat digital voice adapter that runs with ircDDBGateway and DStarRepeater for D-Star for example. As the circuit is a little more complicated than a simple transistor circuit I decided to look for some software that allows for designing the circuit on a breadboard PCB. I decided to go for blackboard as a first try. This software is available as Open Source from  and is written in Java and should run on all major operating systems.
The software allows for basic design of the circuit with basic components without regard to values. I put the parts together on a PCB that is slightly longer than the Arduino. It fits on top as the original MMDVM does. As I had a double layer breadboard I used top and bottom side for wiring. The circuit paths on top are outlined in red and the bottoms ones in blue. There are some areas where the bottom paths are overlayed by the top ones. So for reproducing this circuit I recommand to use blackboard because that allows for blanking one of the layers. The file for blackboard can be downloaded here:
After building the board from the blackboard draft I burned the MMDVM firmware from  into the Arduino and running the MMDVMCal program () I realised that the circuit was not working as expected. None of the LEDs was showing any activity on toggling the PTT. Just the power LED was lit. After some research I found out that there are different Arduino board layouts in the world each having a little different pintout or at least numbering. That issue could be resolved by switching the board layout in the MMDVM Firmware using the Arduino IDE. I just ahd to switch from ARDUINO_DUE_PAPA to ARDUINO_DUE_ZUM in Config.h.
With this modification worked as expected. I used ircDDBGateWay and DStarRepeater from  and configured DStarRepeater to use the MMDVM. After compiling I connected it to an XRF reflector to receive some audio. My ICOM R2500 decoded the D-Star QSO instantly while the ID-51 resisted. So I did some turns on the trimmers for TX and afterwards also the ID-51 was fine with decoding.
A little recording of my first QSO using the MMDVM adapter with DL6EAT can be found on YouTube unter .
Veel radio experimenten kunnen eenvoudig met een RTLUSB stick plaatsvinden. Als je verder wilt experimenteren dan alleen bijvoorbeeld met de SDR# software is GNU radio misschien een optie. Vandaar deze post met een training voor GNU radio. In 11 lessen wordt veel duidelijk gemaakt over dit fantastische stukje software.
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Vaak hebben porto’s die gebruikt worden voor de amateurradio hobby een IP rating. Zeker de radio’s die eigenlijk voor professioneel gebruik hebben deze rating. Hieronder vind je de uitleg over de zogenaamde Ingress Protection.
IP Rating Explained
The inside of two way radio is filled with sensitive electronics which needs to be protected from the outside environment therefore, when you are in process of choosing the most suitable two way radio you might have a look at its IP ratings.
IP ratings are internationally agreed standards of INGRESS PROTECTION. In simple terms it means how well is the radio protected from dust and moisture.
These standards have been agreed to help guide the end users (and sellers like us) to choose/ or recommend the most suitable radio system depending on the end users’ needs.
IP rating is described by two digits where the first represents protection against solids and the second digit protection against moisture.
First digit indicates protection from the solids such as dust. This rating ranges from 1-6. Rankings for solid IP are lowest for large objects and highest for the smallest particles. Therefore, when radio has ranking 6 even the tiniest dust particles cannot get in and damage the radio. The two way radios with high first digit are perfect for construction industry or workers in windy environment.
Second digit is representing protection against moisture. Liquid ingress digits are on scale 1-9 where 1 can hold a falling drop of water to 9 which protects two way radios against high-pressure jets of water from several directions. The most common rating is 7 which can waterproof radio for up to 30 minutes in 1 meter of water.
However, you can also find some radios for which first digit is represented by letter X. These radios doesn’t have a dust protection. However, their primary purpose is usage on boats or at ski centres where dust isn’t the primary problem. These radios are usually extremely waterproof. For instance marine range from Icom.
Let’s have a look at some examples:
Motorola DP4400 has IP rating 57. This means that the radio is still very well protected against dust and is also submersible for up to 30 minutes in 1 meter of water.
When we have a look at Motorola DP2400 with IP 55 we can now assume that the dust protection with this radio is still very good however is not so tough on the water, therefore it is not very suitable for outside environments or places where it can get in contact with lot of liquids.
Icom M35 which is from marine radio range has IP rating X7 and by this we can be sure that this radio is toughly water resistant (but not the good option for dusty places).
Motorola XT180 which targets leisure consumers has IPx2 what means it is splash proof and not really suitable for dusty environments.