So what do I need?
The first thing you will need is a site or location for your proposed repeater. The coverage, ideally should compliment existing repeaters in your area to enhance coverage.
The second thing you will need is a licence from your licencing authority. In the UK this is OFCOM and all applications are processed via the Radio Society of Great Britain (RSGB). Their dedicated vetting agents make the process fairly straight forward.
While your application is in think about the equipment you are going to use. In this example I will describe the kit I used to build GB7PP. Other builders may choose to adopt other equipment to build their MMDVM repeater.
Key components
So to build GB7PP I opted for the following:
Gateway Controller: STM32-DVM-USB MMDVM interface (N3XCC)
This is a shield interface which sits onto the GPIO pins of a Raspberry Pi. Its function is to link the Raspberry Pi and the two radios, so they can communicate with the software.
UHF DV Repeater: 2x Motorola GM350 (128 channel version)
These are fairly cheap, built like a brick, and capable of long periods of transmission without over heating issues. It is important to get the 128 channel version if you want to plug your gateway controller straight in without further modification.
Software: Pi-Star (MW0MWZ) & MMDVMhost (DG9VH)
This is an outstanding piece of free software that Andrew keeps up to date. It has all the functionality you require to set up your MMDVM repeater.
Gateway Server: Raspberry Pi 3 B+
The Raspberry Pi is small, cheap and ideal for running Pi-Star software on. You will require 5 volt power to run the Pi and also a suitable SD card to download Pi-Star software onto.
Internet connection: Origin Fibre Broadband - 40Mb on BT Infrastructure
The choice of internet is relatively unimportant but it should be as quick as possible to achieve a good link to the various digital networks.
GMSK Remote Switch : Belkin WeMo
This is a device which allows for remote switching of the repeater power. This is achieved via a mobile phone app. A requirement of the licence conditions in the UK is to be able to remotely shutdown the repeater. You can also shut down Pi-Star from within the software but this only shuts down the software not your transmitter.
Antenna: Diamond X-50N Vertical Collinear (+7.2dB)
Nothing fancy but good enough to transmit a reasonable signal. Beware if you hope to put your antenna on a third parties property or mast they may require a commercial grade of antenna and coaxial feeder. This can be cost prohibitive if you are doing this on your own.
Duplexer: Procom 6 Cavity UHF (-1db)
This enables a single antenna to work with both transmitter and receiver at the same time. These are tuned to the TX and RX frequencies so don't buy this until you have confirmation of your frequencies from OFCOM. Tuning these can be an right pain if you pick the wrong frequencies.
Band Pass Filter: Procom BPF 70/3 on TX line (-1db)
The key function of the BPF is to prevent interferance of the TX signal onto the RX frequency. These are also tuned to the TX frequency so like the duplexer don't buy this until you have confirmation of your frequencies from OFCOM.
LNA Preamplifier: LNA 70cm-EME by VHFdesigns.com on RX line (+18db)
This simply increases the receive signal so weaker stations can access the repeater.
What next?
Once you have your location, your licence you can order your duplexer and band pass filter. The next part just requires time and some help. You need to put up your antenna at the chosen location, interface your Raspberry pi, Gateway controller and two radios. Don't forget that you will need to program your radios with the RX and TX frequencies. Remember to set the power level as set in your licence.
Get your setup right and you will have a great repeater which enhances our hobby.