Week 8 – Setting TX & RX Offset

After setting up the MMDVM duplex hotspot board, it is necessary to adjust the transmit and receive offsets in the MMDVMHost expert editor section. Basically this corrects the transmit (TX) and receive (RX) frequency of the board, if they’re not on frequency.

I went to a fellow amateur radio operator’s house recently to test my board with his HP 8920A Service Monitor. According to this ham, the service monitor is about 30 years old and cost around $30,000 new. Every 2 years he has it calibrated to NIST standards and it is accurate to +/- 1 Hertz.

The back of the board recommends a TX and RX offset of 500 and then tells you to adjust until the BER or Bit Error Rate is less than 5%. With my friend’s help, I tested the output frequency of the repeater/hotspot board without setting any TX offset and the transmit frequency (FRQ) was about 442.999300Mhz. So I adjusted the TX offset to 500 and retested the transmit frequency. It appears to be getting closer, showing a frequency of about 442.999700Mhz. So I bumped the TX offset up to 800 and that brought the TX frequency up to approximately. 443.000000Mhz, which is right on frequency.

Setting the RX offset is a bit more difficult because there isn’t really a way to test that within Pi-Star. So, I transmitted to the repeater board with my DSTAR handheld and found that I had a bit error rate of 0.1% which really doesn’t need to be fixed.

0.1% Bit Error Rate

I set the RX offset equal to the TX offset (800) and that brought the bit error rate down to 0.0%, which is perfect.

0.0% Bit Error Rate

I also worked on installing the Nextion Display Driver, however I’m encountering problems with it. The screen layout disconnects from the MMDVMHost software every time the screen changes. I need to work on this a little bit more to solve that problem. I’m thinking the problem is the layout I used. I was testing with a layout from another ham that displays a lot of information and I think the screen has trouble keeping up with the amount of data. I will detail this process in my next post.

Week 7 – Configure DSTAR Mode

First we’ll go turn on the DSTAR digital mode and configure it.

  1. Start by going to your PiStar dashboard in your web browser.
  2. After logging into your dashboard, click on the “Configure” tab.
  3. Next we’ll turn on DSTAR in the MMDVMHost Configuration.
  4. Notice that I also set the RF Hangtime and Net Hangtime to 5 seconds. The hangtime is the amount of time the MMDVM will stay in that mode before allowing other digital mode signals a chance to reach the repeater. RF Hangtime is the amount of time the MMDVM waits after the end of an incoming RF (Radio Frequency) signal. Net Hangtime is the amount of time the MMDVM waits after the end of an incoming network transmission from a distant station.
  5. Click “Apply Changes.”
  6. After the changes are applied, scroll down and you will see a new configuration box named “DSTAR Configuration.” The defaults will look like this:
  7. Here are my settings for DSTAR and I’ll explain them after the photo.

Explanation of Settings

  1. RPT1 Callsign – This is the callsign of the node or repeater with its module letter. B = 70CM / C = 2M
  2. RPT2 Callsign – This is the callsign of the gateway, which in our case will be the same as the repeater, but instead of module “B” it will be “G” for “Gateway.”
  3. Remote Password – This is the password used by the ircDDBRemote application as well as the command-line Remote Control application.
  4. Default Reflector – This is the default reflector that the repeater will connect to. A reflector is like a group chat or conference server for many repeaters to connect to. Note that this can be set to “Startup” or “Manual.” I chose “Manual” because I do not want my repeater to automatically connect to a reflector when the repeater turns on.
  5. APRS HOST – APRS stands for Amateur Packet Reporting System and allows data like GPS coordinates, altitude, speed, etc to be reported to other amateurs. This data can be viewed online at a few sites like https://aprs.fi the “rotate” APRS Host is a round robin server according to http://www.aprs-is.net/aprsservers.aspx
  6. ircDDBGateway Language – Select your language and country code if applicable. I selected “english_(US).”
  7. Time Announcements – If turned on, the hotspot/repeater will announce the time every hour.
  8. Use DPLUS for XRF – I don’t use XRF reflectors, so I left it turned off, but this would allow you to use the DPLUS protocol to connect to XRF Reflectors.

Later this week, I’ll discuss programming your DSTAR radio as well as enabling DMR. I’ll also be adding a Nextion Display to this project and attempting to create my own Nextion Display layout in the Nextion Editor Software.

Week 7 – Update MMDVM HS Duplex Firmware

To start this week, I updated the firmware on the duplex MMDVM hot spot board. Follow the steps below to do that.

From where I left off previously, I still needed to select the board/modem in the configuration first.

Selecting the Board

  1. Login to the Pi-Star dashboard and click on the configuration page.
  2. Under “General Configuration” find the option that says “Radio/Modem Type.” and select the MMDVM board that you’re using. In my case I selected the MMDVM_HS_DUAL_HAT for Pi (GPIO).
  3. After making your selection, don’t forget to click “Apply.”

Update MMDVM HS Duplex firmware

Next we’ll update the firmware.

  1. First open the “expert” tab and then click “SSH Access.”
  2. Login with the pi-star user.
  3. Run the following command:
    sudo pistar-update
  4. When the update is complete you should see the following:
  5. Next, restart the Raspberry Pi by going to the “Admin” tab and clicking “Power,” then click “Restart/reboot.”
  6. For the MMDVM_HS_DUAL_HAT board with the 14.7456 TXCO like I’m using, you will want to run the following command:
    sudo pistar-mmdvmhshatflash hs_dual_hat

Reference: https://github.com/juribeparada/MMDVM_HS

Week 6 – Hardware

Last week I decided to purchase a little board called an MMDVM_HS_HAT_DUPLEX. What I purchased is a cheaper clone, but it should work about the same as it uses the same firmware. Essentially it is a tiny low-powered repeater on a single circuit board. It is designed to be a personal duplex hotspot.

MMDVM_HS_HAT_DUPLEX

The board has an STM32 microcontroller and two ADF7021 radio microchips. The board should produce about 10mW of RF power output. The board has a number of LED’s to indicate various things such as, power, carrier operated squelch (COS), Push-To-Talk (PTT), and an LED for each digital mode the board is capable of such as DSTAR, DMR, YSF, P25, and NXDN.

MMDVM Digital Mode LEDs

The board is a hat so it sits directly on top of the Raspberry Pi and uses the Pi’s GPIO pins to communicate with the Pi-Star Software.

MMDVM & Raspberry Pi GPIO Connection

Fully assembled, this is what the Pi looks like with the MMDVM Duplex Hot Spot board attached.

MMDVM_HS_HAT_Duplex on Raspberry Pi 3b

The other piece of this project that I decided to add, was a screen. It has not arrived yet. This will solve the problem of not knowing the IP address of the Pi to connect to the dashboard. I did some reading and the MMDVM Duplex Board is capable of working with a small OLED display OR a Nextion touch screen. I opted for the touch screen which will give me more options for controlling the device. On most of the forums and Facebook groups for DSTAR hotspots, other hams seem to recommend the 3.5″ display most often. I opted for a slightly smaller 3.2″ display, specifically the NX4024K032_011R.

Nextion Display

It’s slightly cheaper than the 3.5″ screen and slightly smaller. This is an enhanced version with more flash memory and more RAM than the basic models.

Nextion Editor Layout

This display is a Human Machine Interface that is programmed using a piece of software called Nextion Editor. It’s a What You See Is What You Get (WYSIWYG) editor. The coding to make the screen work seems pretty simple, however I have not looked at the code in the Pi-Star software that actually sends the information to the screen.

Here I found a guide on using the Nextion Editor software, which I’m sure will be useful for creating my own display interface. Here is another guide on creating a screen layout/interface that is specific to the MMDVM and ham radio. The interface is designed, saved to an HMI file, and then compiled into a TFT file, which is then uploaded to the screen. You can upload the TFT file via a USB to TTL serial adapter or by using a microSD card with the TFT file on it, inserted into the microSD card slot on the Nextion Display.

USB to TTL Serial Adapter

You may also find *.TFT files that other amateur radio operators (hams) have made available on a few different MMDVM Hotspot groups. These files (as long as they’re made for the exact screen you’re using) can be downloaded to your computer and uploaded to your screen. If you can get the *.HMI file which is typically available with the *.TFT files, you can edit the HMI file in Nextion Editor to suit your needs and then upload it to your screen. Here is an example interface from the second guide that another ham has created.

UI sample from PD0DIB

Next week I’ll set up the MMDVM to work with the Raspberry Pi and update the MMDVM’s firmware.

Week 5 – PiStar Setup Part 2 of 2

In this post I will explain how to update, upgrade, and configure the basic settings for Pi-Star. I will also explain how to register your amateur radio callsign for DSTAR and DMR use.

Part 1 of this post: https://n3tdm.tdmorris.com/week-4-setup-part-1/

First of all, for this project you MUST be a licensed Amateur Radio Operator. In the USA, that means passing a licensing exam and being assigned a callsign from the Federal Communications Commission (FCC). For licensing information check out the American Radio Relay League.

Register your Callsign for Dstar

  1. Follow the instructions to register your own callsign found here: http://www.dstargateway.org/D-Star_Registration.html
  2. After you receive your confirmation email, go to this page to learn how to assign terminal ID’s to your callsign (STEP 1 only). Terminal ID’s are just what they sound like, it’s an identifier for your individual station. If you’re just using one radio, you can typically set a terminal ID of a single space, however we’re setting up a repeater, so you would need the space terminal ID and whatever module you’re using B for 70CM or C for 2M frequencies.
  3. My terminal ID’s look like the following: 
  4. Here is more information on Terminal ID’s: https://wb1gof.dstargateway.org/DStarTerminalIDs.html
  5. After you’ve registered for DSTAR you need to get a CCS7 ID for DMR.

Get a ccs7 id number for DMR / DSTAR

  1. Head over to this site and fill out the form selecting the option for a private callsign and NOT a repeater. I’m going to be setting up a private repeater for experimentation so it won’t be running 24/7.
  2. Once your request is processed, you’ll receive an email containing your CCS7 ID number. Put that in a safe place.

Setup and Configure wifi

In order to configure this, because I had no way of getting the IP address from a headless Raspberry Pi, I connected a crossover cat5e cable between the Pi and a PC so I could connect into it and make adjustments.

That said, I want to first explain how I setup the enterprise WiFi for the Pi to work on Pitt’s wireless network.

    1. I followed the instructions located here: https://gist.github.com/chatchavan/3c58511e3d48f478b0c2
    2. First open a new tab in your browser and go to
      Windows: http://pistar/admin/expert/ssh_access.php
      macOS: http://pistar.local/admin/expert/ssh_access.php
    3. Enter “pi-star” without the quotes for the username and press enter.
    4. Enter “raspberry” for the password without quotes and press enter.
    5. You should be greeted with a screen spelling out PI-STAR.
    6. Now type
      sudo nano /etc/networking/interfaces
    7. You should see the following screen:
    8. Use the arrow keys to navigate the page and move down to the section that says
      allow-hotplug wlan1
      iface wlan1 inet manual
              wpa-conf /etc/wpa_supplicant/wpa_supplicant.conf
    9. Erase the section above and enter the following:
      auto wlan0
      allow-hotplug wlan1
      iface wlan1 inet dhcp
      	pre-up wpa_supplicant -B -Dwext -i wlan1 -c/etc/wpa_supplicant/wpa_supplicant.conf
      	post-down killall -q wpa_supplicant
    10. Press CTRL+o and press enter, then press CTRL+x to exit the nano editor.
    11. Then go to the Configuration page of your Pi, then to the Expert tab, then click “WiFi” in the “Full Edit” line of editors.
    12. You should see a list of networks (probably just one) after a header of sorts
    13. Make sure the country code following “country=” matches your country code. In the USA it’s “country=US” without quotes.
    14. For the enterprise wifi you need to make a new network in this config file. For WIRELESS-PITTNET at the University of Pittsburgh at Bradford, I used the following settings. In this editor I set up the following network:
    15. Go back to your SSH access page in your browser and do the follow steps.
    16. Enter the following substituting YOUR_PASSWORD with your university email password leave the single quotes around your password. and press enter.
      echo -n 'YOUR_PASSWORD' | iconv -t utf16le | openssl md4
    17. Next copy the resulting random letters and numbers into the WiFi editor in the other tab after the colon where it says “password=hash:”
    18. Now go back to your SSH editor and clear your history by typing:
      history -c
    19. Press “Apply Changes” at the bottom of the page beneath the wifi editor.
    20. If you followed these steps correctly your pi should connect to WIRELESS-PITTNET.

Configure Pi-star

  1. In your browser go the main page of your Pi-Star dashboard at:
    Windows: http://pi-star/
    macOS: http://pi-star.local/
  2. You should see the following page:
  3. Start by selecting MMDVMHost and Duplex (repeaters) or Simplex (personal hotspots), then click apply changes.
  4. After the services are restarted, you should see the following page:
  5. I started the configuration process without the actual interface board, keep that in mind. I did not activate any services yet, however I set the hostname, the node callsign, the RX/TX Frequencies, the GPS coordinates, the town (in the format of “city”, “grid locator”, the country, the URL (this can be either a manual URL of the dashboard for the repeater or automatic and will default the QRZ page for the node callsign), the node type (public – anyone can use it / private – only the node callsign can use it), the time zone, and the dashboard language_country code.
  6. You can also setup the firewall if you wish. Private makes it only work within your local network, public will make it work from outside your network provided the correct ports are forwarded on the router.
  7. I left Auto AP on because if the Pi doesn’t/can’t make a network connection, it will create a wifi hotspot of it’s own so you can connect to it and configure the network settings.
  8. I left UPNP turned off. If your router also has UPNP, you can turn this feature on and Pi-Star will configure your router’s firewall to open the necessary ports.

I found a neat little circuit board on eBay that works with MMDVMHost software and is a mini personal repeater on a single board. I thought this would be a great way to demonstrate a repeater without having to bring in multiple radios, a power supply, the computer, etc. So I’m going to use the MMDVM_HS_Dual_Hat. The board on eBay is a cheaper Chinese “clone” of the original board which is pictured below.

Week 4 – PiStar Setup Part 1 of 2

This week, I began the installation and configuration of the Pi-Star software on a Raspberry Pi 3B. In this post I will walk you through step by step, how to image the microSD card. I will also discuss setting up a home WiFi Network. In the next post, I’ll talk about configuring the basics of PiStar including enterprise WiFi networks and hashing the WiFi passwords.

First you’ll need the following:

  • Pi-Star Software – You’ll want to download the one for the RPi
  • WiFi (wpa_supplicant) Configuration File (basic USA file can be found here)
  • Blank microSD Card – Class 10/UHS-1 – backup data first if needed
  • MicroSD to SD Card Adapter (Optional – depends on your PC)
  • Raspberry Pi 3B
  • Raspberry Pi Power Supply of 2 amps or greater
  • PC with SD Card or MicroSD Card reader/writer
  • SD Card Imaging Tool (Etcher, Apple Pi Baker, Win32DiskImager)

Tutorial

Download the Files

  1. The first step is to download the Pi-Star software using the link in the list of parts. At the time of this writing, the version for the Raspberry Pi is “Pi-Star_RPi_V3.4.16_10-Aug-2018.zip”
  2. Download the wpa_supplicant.conf file. If it opens as a web page, simply copy the contents of the file and paste it into Notepad or Text Edit and save as “wpa_supplicant.conf” without quotes.
    1. In the file, replace the capitalized “SSID” with your network name.
    2. Next in the file, replace the capitalized “PSK” with your network password.
    3. Save the file making sure that the filename is wpa_supplicant.conf.

Imaging the microSD Card

  1. First, we’ll download an SD card imaging tool. For general imaging uses, I like to use a software called Etcher, which is available for Mac, Windows, and Linux. If you need to backup an SD Card, I use a tool for Mac called Apple Pi Baker. You can also use this tool to image SD Cards and it allows you to backup/restore an SD card to/frome a compressed file (.zip, .gzip, .7zip, etc). For Windows there is a program called Win32DiskImager which will allow you to backup or image an SD card in the uncompressed “.img” format. In this tutorial, I’ll use Apple Pi Baker on a MacOS PC.
  2. I’m not going to cover backing up the SD card in this tutorial, but if you have anything on your card that you want to save, be sure you have backed it up first as the following steps will ERASE everything on the card.
  3. First insert the microSD card into the SD card adapter and insert the adapter into your computer. Be sure the switch (if any) on the adapter is in the up position to allow the computer to write to the card.
  4. Next, go to the folder you downloaded Pi-Star into and double click the .zip file to extract its contents. It will be a folder that is extracted.
  5. Double click the folder to enter it and make sure there is a file around 2.5-3gb in size named with a “.img” extension.
  6. Next open Apple Pi Baker and enter your administrator password if prompted. The admin password is required to allow the app to write directly to the SD card device.
  7. Next you should see a screen that looks like this:
  8. Select your SD card in the box under Pi-Crust. Mine isn’t shown in the photo above because it wasn’t inserted when I opened Pi Baker. Just click the green refresh button to the top right of the white box and it should show up.
  9. Be 100% sure you’ve selected the correct SD Card/drive in the Pi-Crust Section. If you have other SD cards or flash drives inserted they may show up as well. SELECT THE CORRECT DRIVE. ALL DATA ON THE SELECTED DRIVE WILL BE ERASED.
  10. Under Pi-Ingredients, click the 3 dots button and find the Pi-Star .img file we found in step five.
  11. Uncheck the “Auto eject after successful restore” checkbox.
  12. Next after you are certain you have everything set correctly and have selected the correct SD card, you’ll click “Restore Backup” in the Pi-Ingredients Section.
  13. You should see a screen like this:
  14. Wait until you get the notification that the process is complete and then you can close Pi-Baker.

Setting Up HOME WiFi

  1. Open Finder or My Computer (This PC) and locate the wpa_supplicant.conf file you edited previously.
  2. Copy the file by right clicking the file and left clicking copy.
  3. Navigate to the SD card which should be labeled “Boot”.
  4. Paste the copied wpa_supplicant.conf file by right clicking in the space free of any files and click paste or just press CTRL+V (Windows) or CMD+V (macOS) to paste the file.
  5. Close Finder or Windows Explorer.
  6. Eject or Safely Remove the SD card. On macOS, drag the SD card to the trash bin or click the eject button next to it in Finder. On Windows, in My Computer or This PC, right click the SD card and click “eject.”

First Boot

  1. Insert the MicroSD card into the Raspberry Pi and plug in the power cord.
  2. The LED on the Pi should light up red, with a flashing green LED next to it.
  3. Wait a few minutes as the Pi will load the WiFi configuration and reboot.
  4. From your PC, connected to the same WiFi network you setup the Pi on, open your web browser and go to one of the following sites:
    1. http://pi-star/  (Windows)
    2. http://pi-star.local (macOS)
  5. Verify that you see something similar to the following:
  6. I’ll continue the setup in the following post: https://n3tdm.tdmorris.com/week-5-setup-part-2

Week 3 – DSTAR Repeaters

Last week, I decided to use a software I’ve worked with in the past, called Pi-Star to setup a digital multimode amateur radio repeater. This week I did a bit more research on DSTAR and found some diagrams to hopefully explain things a little better. If you aren’t familiar with what a ham radio repeater does, there is a diagram below.

Basically a repeater listens on one frequency and simultaneously retransmits what it “hears” on another frequency. Typically a repeater is at an elevated location (i.e. a mountain top, tall building, etc), running a high performance antenna system and higher power output.

How does a digital repeater work? It works in much the same way as a regular repeater, however with DSTAR, there is often an internet link via a computer added to the repeater as shown below.

The diagram above is of one digital mode called DSTAR, but most digital modes work similarly in respect to the hardware required. In a DSTAR repeater there is a radio connected to an interface board which is then connected to a computer (usually either a PC or a Raspberry Pi). The computer makes and manages the connections through the internet to other repeaters or reflectors (conference servers). The computer makes these connections based on commands sent over the radio, sent through a remote control application, or sent through a web interface. An example of the Pi-Star web interface for the KC3ESS DSTAR repeater that I help manage is included below.

The dashboard lists the timestamp of the transmission, the target (where the transmission is intended to go), the RPT 1, and RPT 2 callsigns.

The target of a transmission tells the computer what to do, so CQCQCQ means that the transmission is intended for everyone to hear, REF030CL tells the computer to link to reflector 30C, and _______U, tells the computer to unlink from the current connection.

The RPT 1 callsign is the callsign of the repeater/hotspot/reflector that the transmission is being received by and forwarded to the internet from. In this photo the RPT 1 callsign, KC3ESS_B means that the transmission is going through the KC3ESS repeater and the B means a frequency in the UHF 70 centimeter band (420Mhz to 450Mhz). The callsign may also be REF063C which means the transmission is being received over the internet from reflector 63C.

The RPT 2 callsign is the destination callsign. In the photo above we have, KC3ESS_G, which means the destination of the transmission is the internet gateway on the KC3ESS repeater. Essentially that tells the computer connected to the KC3ESS repeater to send the transmission over the internet. If this were set to KC3ESS_B, the transmission would never leave the local KC3ESS repeater.

The target or URCALL field, RPT1 field, & RPT2 field all work together to route the DSTAR transmission to the appropriate location within the DSTAR network.

I also created a Gantt Chart for this project with a list of tasks.

Photos link to their respective sources.

Week 2

This week I continued my research on digital repeaters and software. I’ve decided to use a Raspberry Pi with the Pi-Star image, which contains software used to setup, configure, and maintain a digital repeater. It’s the most complete package I’ve seen and is widely recommended by other hams running digital repeaters. I have worked with this particular software package before so I have some understanding of how it works and how to use it. It basically contains many pieces of software which work together to manage and control a digital repeater. It can also be used to control digital multimode hotspots (duplex or simplex hotspots).

Pi-Star contains the popular digital radio software created by Jonathan Naylor, G4KLX: ircDDBGateway, DSTARRepeater, DMRGateway, and MMDVMHost. It also contains a complete dashboard and can support a wide variety of hardware. MMDVM stands for Multi Mode Digital Voice Modem.

The Raspberry Pi is a great piece of hardware for projects like this due to its cost, reliability, availability, and small size. I will be using the one I have already, a Pi 3B.

Week 1

This week I have gathered some of my personal knowledge on digital repeaters in order to create a project proposal for a digital multimode amateur radio repeater.

I have been involved in amateur or ham radio for about nine years now. In the most recent 4 or 5 years, I’ve been working on DSTAR repeaters and now it’s time to branch out to DMR repeaters as well. Amateur radio is a two way radio service that allows other amateur radio operators to communicate with one another using various modes including: Morse Code, voice, text messaging, email, images, television (SSTV), and other digital modes like DSTAR, DMR, Yaesu System Fusion, P25, etc.

I also created this website and got SSL installed on the server. I put together a portfolio of some of the websites I have built in the past and will work on a Gantt Chart and resume next week.

For my capstone I’d like to build a multimode digital repeater that will operate with at least two modes, probably DSTAR and DMR. I’m much less familiar with DMR, than I am with DSTAR.