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.


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 wlan1
      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.