Building a Simplex Hotspot (MMDVM) Hardware

Contents:

Introduction
What is a Hotspot?
Hotspot Hardware
MMDVM
Hardware Construction
Further Reading

Introduction

This is a simple setup guide to assemble your Simplex Hotspot hardware. Credit for much of this material goes to VK4MWL in his setup guide, VK4MWL-VKDMR_Hotspot_Setup_v1.3.pdf

[Top][Home]

What is a Hotspot?

A Hotspot is like a mini repeater with a limited range due to the low power output of approximately 10mW. Your handheld connects to the Hotspot using RF and then the hotspot connects to the DMR Server over the internet.

A hotspot is useful for areas that do not have easy access to the local DMR repeater. If a repeater is available it should be used in preference to a hotspot.

Unfortuantly, by far the majaority of hotspots in service are simplex, That is they have only one radio chip. At a litytle extra cost a duplex hotspot with two radio chips are superior as it allow the hotspot to operate on both TDMA slots similtaneaously.

[Top][Home]

Hotspot Hardware

There are several different Hotspots on the market. This document covers the chinese made Jumbospot MMDVM Hotspot, also known and the Zumspot nwhich was the original MMDVM board that was designed by Jim Mclaughlin, KI6ZUM, based on the MMDVM work by Jonathan Naylor, G4KLX and others, with firmware by Andy, CA6JAU.

This guide uses the following components:

Raspberry Pi Zero W (Single Board Computer that runs Linux)
Jumbospot MMDVM board (Multi Mode Digital Voice Modem - UHF Radio Board)
OLED Display (Usually supplied with the MMDVM board)
Metal Case
UHF Antenna
16GB MicroSD memory card
Dual row header pins

These parts can be sourced separately or purchased as a kit. VKDirect (https://vkdirect.com.au). have kits available.

Alternatively you can buy parts from the below websites :- - https://core-electronics.com.au/ (Raspberry Pi, Power Supply, SD Card) - Aliexpress - eBay

Raspberry Pi Zero W

There are two versions of the Raspberry Pi Zero W and Raspberry Pi Zero WH. The “W” version does not come with headers and the “WH” version includes headers pre-soldered.

If you get the one with headers already soldered as shown in the photo here you will need snip pins 12,14,16,18 so they do not interfere with the pins from the OLED display.

The MMDVM boards come with 2 sets of 2x5 header pins that can be soldered to the Raspberry Pi, so if you can solder in the pins, I recommend that you buy the Raspberry Pi Zero W as it is cheaper.

[Top][Home]

MMDVM

This board provides the RF interface between the Raspberry Pi and your DMR radio.

[Top][Home]

Hardware Construction

Solder the 2 sets of 2x5 header pins to the component side of the Raspberry Pi Zero W where required
Separate the 2 case pieces. Note that one end has an oval hole this must line up with the SDCard slot of the Raspberry Pi
Install the Raspberry Pi into the lower case using the 2 short screws next to the header pins. Note the SD Card Slot is on the left in the photo.
Install the MMDVM Board by plugging it into the Raspberry Pi. Note that the pins from the OLED are not touching any of the pins on the Raspberry Pi.
Use a pair of long nose pliers or tweezers to hold the two plastic spacers while installing the 2 long screws.
Align the SMA connector on top of the MMDVM board with the top part of the case and clip the case into place. Note the case should easily clear the connectors on the Raspberry Pi, if it doesn’t check that the Raspberry Pi is installed in the correct orientation with the oval hole on the SD Card side of the Raspberry Pi.
Screw on the antenna. Don’t install the SD Card Yet as we need to install the software onto it.

[Top][Home]