Build your own homebrew MMDVM hotspot

Material section

The interface board

This board is a PCB that has the objective of simply connecting the STM32F103 microcontroller to the ADF7021 UHF transmitter. As an accessory, LEDs have been installed to display the functioning (active mode, transmission…) and other connectors to possibly add a screen. This is not essential for operation. So I didn’t solder anything on the board, except for the P4 connector that will be used for load the firmware (HOST_RX and HOST_TX signals). I only installed the two modules (STM32 and ADF7021).

Schematic MMDVM HotSpot.PDF

All the resources to make this PCB are available on DB4PLE GitHub (for Kicad software). You can also download it directly here.

MMDVM_HS_PCB_Single.zip

Oscillator Replacement on ADF7021

You can obtain the board 433 Mhz ADF7021 for example on aliexpress.

On the ADF7021 board, we need to replace the TCXO in place with another model with a frequency of 14.7456 MHz. You will find this TCXO in the same dimensions as the original (3.2 mm x 2.5 mm) under the part number ECS-TXO-3225-147.4-TR (Available from Mouser for example).

This operation is delicate but can be carried out with a soldering iron equipped with a fine tip and a tweezer. Patience and precision will help you also…


If you would be interested to participate in a possible future new grouped order (MMDVM board, SvxLink Card), leave your email below to be reported!

12 thoughts on “Build your own homebrew MMDVM hotspot

  1. Bonjour,
    très beau tuto Christian, merci !

    Bruno

    (Translation)
    Hello,
    Very nice tutorial Christian, thanks !

    Bruno

  2. Hello, I have been reading your very informative website, as I am in the process of setting up my Hotspot.
    The question I have is what UHF frequency do you set your MMDVM to?

    Is it a special simplex frequency which is also programmed into your P25 ,DMR, Fusion, D-Star radios?

    Or is it a UHF frequency of a local reflector to your QTH.

    73
    Colin
    Sydney Australia

    (Traduction)
    Bonjour, J’ai lu votre site très instructif, car je suis en train de mettre en place mon Hotspot.
    La question que j’ai est : quelle fréquence UHF définissez-vous votre MMDVM?

    Est-ce une fréquence simplex spéciale qui est également programmée dans vos radios P25, DMR, Fusion, D-Star?

    Ou est-ce une fréquence UHF d’un réflecteur local à votre QTH.

    73
    Colin
    Sydney, Australie

    1. Hello Colin,

      The frequency of the hotspot is to be programmed in your stations in simplex (RX = TX).
      For example 435000
      Regards

      (Traduction)
      Bonjour Colin,

      La fréquence du hotspot est à programmer dans vos postes en simplex (RX=TX)
      Par exemple 435000

  3. where is the PCB info file for gerbers and or also where can the PCB be made
    (Traduction)
    où est le fichier d’information PCB pour les gerbers et ou aussi où le PCB peut-il être fait?

  4. What is the current usage of the adf and stm and it be connected to the pi by a usb connection

    (Translation)
    Quelle est la consommation actuelle de l’adf et du stm et lorsqu’il est connecté au pi par une connexion usb?

    1. Trent,

      I just measure, the electrical power consumption of this hotspot using a Raspberry Pi 3 is 0,36A under 5,25V. When disconnecting the hotspot (remains alone the pi), then the current is down to 0,34A.

      73

      (Traduction)

      Trent,
      Je viens de mesurer, la consommation électrique de ce hotspot fonctionnant avec un Raspberry Pi 3 est de 0,36A sous 5,25V. Lors de la déconnexion du hotspot (seul le pi reste) le courant est réduit à 0,34A.
      73

  5. Il suffit de bien suivre Le tuto et ça fonctionne.
    L’ensemble “zumspot libre” ainsi programmé fonctionne très bien logiciel pi-star.
    73 à tous F5jwx.

    (translation)
    Just follow the tutorial and it works.
    The “free zumspot” set thus programmed works very well pi-star software.
    73 to all F5jwx

  6. Bonjour
    Merci pour tous vos tutos.
    J ai une question sur le module RF7021SE.
    Serait il possible de utiliser ce module en RX dans un relai mmdvm afin de remplacer un TRX Motorola ou autre. Est il suffisamment sensible ?
    Merci de votre retour
    73
    Manu f4flq

    (Translation)
    Hello
    Thank you for all your tutorials.
    I have a question about the RF7021SE module.
    Would it be possible to use this module in RX in a mmdvm repeater to replace a Motorola TRX or other. Is he sensitive enough?
    Thank you for your feedback
    73
    Manu f4flq

    1. Bonjour Manu,

      La datasheet du composant ADF7021 indique une bonne sensibilité théorique de -122 dBm, soit 0,18 µV (pour modulation 2FSK). J’ai donc l’impression que cela doit pouvoir être un bon récepteur.

      Pour en faire un relais, il vous faudra fonctionner MMDVM_HS en mode duplex, avec 2 ADF7021. Voici un exemple.
      MMDVM Full duplex
      Vu sur https://twitter.com/quini7620/status/944580784031232000

      (Translation)
      Hello Manu,

      The datasheet of component ADF7021 indicates a good theoretical sensitivity of -122 dBm, i. e. 0.18 µV (for 2FSK modulation). So I have the impression that it must be a good receiver.

      To make it a repeater, you will need to run MMDVM_HS in duplex mode, with 2 ADF7021. Here is an example.

      Viewed on https://twitter.com/quini7620/status/944580784031232000

Leave a Reply

Your email address will not be published. Required fields are marked *