Configuring Pi-Star for the STM32-DVM-MTR2K


Disclaimer: The following tutorial was written by Justin Reed (NV8Q) and is provided without warranty or support. I do not have official involvement with the MTR2K boards other than I own and use several. This guide assumes you are already familiar with writing an image to an SD card and configuring Pi-Star in a hotspot or STM32-based repeater. If this is your first rodeo with Pi-Star or MMDVM, this guide will not hold your hand through the simple stuff.

Due to popular demand, I’ve finally gotten around to writing a short configuration guide for using Pi-Star on the STM32-DVM-MTR2K board. This guide covers all variants of the board.

First, download the Pi-Star image for the NanoPi here: http://www.pistar.uk/downloads/

Note: Be sure to get the NanoPi image and not the NanoPi_Air version.

Once that file is downloaded, unzip it using your favorite unzip software. This will produce the original file in .img format.

Then, using a quality micro SD card (class 6 or faster) at least 4MB in size, download and use Win32DiskImager (or your favorite disk imaging program) to write the image to the card. Insert this card into the NanoPi Neo, slide the STM32-DVM-MTR2K into the middle slot of your MTR2000 station, connect the Ethernet port to your network and power up the station. (Antenna/dummy load connected to the TX, right?)

At this point, it needs to be pointed out that the OS that Pi-Star is built upon requires a connection to a network that has a DHCP server running or it will block and not fully boot. You don’t necessarily need to be on a network connected to the internet but at a minimum the Pi will need a link to a network with DHCP enabled. If your repeater is going to be used as stand-alone with zero network attached, you will want to use the MMDVM software that Cort includes with the MTR2K boards. Alternately, you can just buy a cheap router and enable DHCP and Pi-Star will work standalone.

Once you’ve powered up the station and waited a minute or so for the software to load, using a web browser on another computer connected to the same switch/router the station is connected to, browse to http://pi-star.local/ and enter the default credentials. Be sure to change your password at first opportunity.

Since our primary (or only) mode of operation in the KS-DMR system is DMR, and DMR is the most level-critical mode, that’s what our config and alignment will focus on.

After you’ve completed the basic configuration, click into the Expert > MMDVMhost window. Scroll down to the ‘Modem’ stanza which will look similar to this:

A sample MMDVMhost modem config from a working environment.

Be sure that TXInvert and RXInvert are set to 0 (zero), and DMRDelay is set to 165. The other fields are not critical other than I suggest your levels are around 50. The actual level alignment will be completed in the MTR2000 RSS. Apply the changes after you’ve written new values.

Once that is done, click here to learn how to align the levels on the MTR2000 station.

After you complete the alignment you should have a working MMDVM repeater. This really leaves us with just one other piece: RSSI. This is by no means mandatory, but a lot of folks like to use the RSSI feature in MMDVM. The modem stanza within MMDVMhost allows you to specify a location for a mapping file to hold the measured value of the MMDVM RSSI ADC input, and the corresponding signal level in dBm. The file can be directly edited via the http interface in Pi-Star by browsing to the Expert > RSSI Dat page. Not everyone has the means to calibrate RSSI, so I wanted to offer my RSSI.dat from a typical MTR2000 equipped with a V2.0 board. Please understand that you’ll want to do a calibration for each radio for maximum accuracy. If you don’t have the means to do this, or absolute accuracy isn’t that important to you, the numbers below should get you pretty close:

The STM32-DVM-MTR2K will saturate the MMDVM ADC input at signals much stronger than -30dBm. That’s ok, I did that on purpose in order to keep the signal level at the low end up a little higher in order to improve ADC resolution for weaker signals.

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