Tag: radio technology

Week 11 – DMR Deviation & Case

I enabled DMR last week and spent some time configuring it. This week I had to set the DMR transmit deviation in order to get it to work.

Essentially setting the TX deviation for DMR is the same as how I set the transmit deviation for DSTAR in the beginning. I used a service monitor and checked the deviation level while the repeater was transmitting. It was lower than it should have been, so I increased the level in the expert MMDVMHost editor on the line that said DMR Level. This adjusted the deviation for just DMR, leaving the deviation alone for all other modes.

I also created a box/case for my project out of a large crayon box that I found at WalMart for about $3.

  1. I used a template for the Pi to drill four holes in this box for some #4 screws to mount the Pi and MMDVM duplex. I also put a piece of acrylic between the Pi and this case so that it wouldn’t be pressing against the back of the Pi.
  2. I then cut out a hole for the size of my 3.2in Nextion Display.
  3. I also drilled holes around the display cutout to mount the display in place.
  4. I used plastic from an old ice cream container to create a bezel to go around the display since part of the display doesn’t show anything and is instead used for the touch screen controller/wiring.
  5. I added two external antenna connectors. I bought two male to female jack/panel mount SMA connector extensions for about $6 each and then I added some right angle SMA connectors (male to female) 5 for about $4.
  6. For the external antennas I drilled the holes in the box as far apart as I could and installed the female jack connectors through the hole.
  7. Then I screwed a right angle SMA connector on each jack.
  8. Next, I used a couple right angle SMA connectors on the MMDVM hotspot/repeater board.
  9. Finally, I installed all of the electronics.Here is the finished case.

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.