aprx and weather reporting

I’ve been sending weather reports via APRS-IS and RF for some years and have recently re-architected the way it works.  My APRS station uses aprx software running on a Raspberry Pi Model B.

My weather station is a Davis Vantage Vue with WeatherLinkIP module. The module allows the weather station to plug directly into my ethernet network. I formerly used WeatherLinkIP to feed the data to CWOP which would in turn show up on APRS-IS.  I would then gateway my reports back to RF using an aprx filter.  This seemed convoluted to me, so I wanted to improve things.

I now use a program called Weather Display, a very capable weather program, which has the capability to generate an APRS WXNOW.TXT file.  Weather Display can directly poll the Davis station via IP.  Through the steps documented below, I now send my weather reports via RF and APRS-IS in the same step.

Every 10 minutes, via crond, I perform some preprocessing on the WXNOW.TXT file to embed the weather report in the APRS “Complete Weather Report Format — with Lat/Long position and Timestamp” and then secure copy the file over to my Raspberry Pi APRS system:

#!/bin/bash
#
if [ ! -f ~/tmp/WXNOW.TXT ]; then
   exit 1
fi
# Change to the Lat/Long of your weather station
LATLONG="4023.75N/07412.53W"
line=0
while read FILE; do
   if [ $line = 0 ]; then
      # Change America/New_York to your timezone
      TIME=`TZ=UTC date --date="TZ=\"America/New_York\" $FILE" +%d%H%M`
      line=$((line+1))
   fi
WX=$FILE
done < ~/tmp/WXNOW.TXT # echo /$TIME\z$LATLONG\_$WX > ~/tmp/wxnow.tmp
# 
echo `cat ~/tmp/wxnow.tmp | tr -d '\r'`XDsIP > ~/tmp/wxnow.txt
# You must setup ssh key based authentication for this to work
# Another method could be a file copy via NFS or CIFS
scp ~/tmp/wxnow.txt pi@aprs:/dev/shm/wxnow.txt
# 
rm ~/tmp/wxnow.txt ~/tmp/wxnow.tmp

On the APRS host, I defined the following beacon section in /etc/aprx.conf:

beaconmode both
cycle-size 10m

beacon via WIDE2-1 \
srccall N0CALL-13 \
exec /usr/local/bin/aprx-wxnow.sh

Finally, the beacon exec script, is installed in /usr/local/bin/aprx-wxow.sh:

#!/bin/bash
#
TIME=$(printf `date -u "+%d%H%M"`)
if [ -f /dev/shm/wxnow.txt ]; then
   if [ -f /dev/shm/wxold.txt ]; then
      FULLWXOLD=`cat /dev/shm/wxold.txt`
   else
      FULLWXOLD=""
   fi
   FULLWXNOW=`cat /dev/shm/wxnow.txt`
   if [ "$FULLWXOLD" == "$FULLWXNOW" ]; then
      # Convert date/times to minutes for date arithmetic
      CURDAY=`echo $TIME | cut -b 1-2`
      OLDDAY=`echo $FULLWXOLD | cut -b 2-3`
      CURHR=`echo $TIME | cut -b 3-4`
      OLDHR=`echo $FULLWXOLD | cut -b 4-5`
      CURMIN=`echo $TIME | cut -b 5-6`
      OLDMIN=`echo $FULLWXOLD | cut -b 6-7`
      CURTIME=$((10#$CURDAY * 1440 + 10#$CURHR * 60 + 10#$CURMIN))
      OLDTIME=$((10#$OLDDAY * 1440 + 10#$OLDHR * 60 + 10#$OLDMIN))
      # If report older than 20 minutes then not updating
      if (( $(($CURTIME-$OLDTIME)) > 20 )) ; then
         echo -n \>$TIME\z
         echo " WX rpt not updating"
         exit 0
      fi
      # Unchanged report but <= 20 min old then don't transmit
      echo
      exit 0
   else
      OLDRPT=`echo $FULLWXOLD | cut -b 9-`
      NEWRPT=`echo $FULLWXNOW | cut -b 9-`
      #if new and old report are same then don't transmit
      if [ "$OLDRPT" == "$NEWRPT" ]; then
         echo
         exit 0
      fi
      # Transmit report and copy wxnow.txt to wxold.txt
      echo $FULLWXNOW cp /dev/shm/wxnow.txt /dev/shm/wxold.txt
   fi
else
   echo -n \>$TIME\z
   echo " WX rpt not found"
fi

While debugging, I noticed that the wxnow.txt file would sometimes disapper from /dev/shm.  This turned out to be systemd cleaning up interprocess communication whenever the pi user logged out.  I fixed this by adding the following line to /etc/systemd/logind.conf:

RemoveIPC=no

Following this change, you must restart systemd-logind.service:

sudo systemctl restart systemd-logind.service

If you implement this on your aprx system, please leave a comment.

Radiation reporting to APRS

A large scale public health/public safety initiative when I worked for the City of New York was NYPD’s radiation monitoring program. Designed to detect a dirty bomb, it makes use of wireless real-time alerting.

Now you can perform your own monitoring as part of your amateur radio station and send the results in real-time to the Automatic Packet Reporting System.

Amateur radio operator “Adminck” (S55MA) in Slovenia has published this blog post. It explains how a Raspberry Pi Zero, a tiny geiger counter, and some scripts are sending his radiation measurements live to the world via the internet.

You can see the actual reports here.

Decode HD Radio on RTL-SDR!

During my 2017 SWL Fest presentation, I mentioned that there is no way to decode either HD Radio or ATSC HD Television using software designed for the RTL2832U dongles. The explanation I provided is that both protocols are covered by patents and that the holders have not been forthcoming on providing necessary details to the open source community.

A cybersecurity researcher, Theori, has cracked the codec used by the NRSC-5-C standard for US based terrestrial digital radio. I am now listening to HD Radio via an RTL SDR dongle. It takes a decent signal, so I’m not getting too many stations using an inside whip antenna, but there are enough to experiment with. It also takes a better dongle with good frequency stability. An older dongle without the TCXO was not up to the task, even on an i7 based system.

The discovery is summarized on the RTL SDR Blog. You’ll need some familiarity with building packages under Linux to grab the source from github and to compile it on your system. So far, I’ve compiled under Debian x86_64, Fedora x86_64, and Raspbian! Next, I want to get it running under Cygwin so that I can use it on the Windows 10 computer in the radio room.

It is a blast to be able to decode the alternate program streams. Audio quality is better than Sirius XM.

Thanks Theori!

DV4mini RPi Image Update

I’ve created an updated image for use with the DV4mini and the Raspberry Pi 2 and 3. It incorporates changes through dv4mini software version date 20170517. It also includes my Brandmeister XTG Dialer for use with extended routing.

Changes include enhacements for YSF reflectors, DMR, DStar as well as the introduction of a text chat window.

Thanks to Ulrich Prinz (DC3AX) for his hard work in support of the DV4 community!

For default passwords, see this post.

Running BMXTG on Windows 10

I’ve been able to run the Brandmeister XTG Dialer on Windows 10 by following this procedure.

Visit the PyGTK FAQ page and fully read 21.1.

I installed the following items referred to in the FAQ:

Python 2.7.13
PyGTK for Microsoft Windows using the all-in-one installer

Run a Windows command prompt as Administrator.

cd \Python27
python -m pip install -U pip setuptools
python -m pip install -U requests

Exit the Administrator command prompt and then open a command prompt as a regular user.

cd %AppData%
mkdir Python

Copy bmxtg-v1.2.zip into your %AppData%\Python directory and unzip.

Create a desktop shortcut to bmxtg.py. The “Target” should be “C:\Python27\pythonw.exe bmxtg.py” and the “Start in” directory should be “%AppData%\Python\bmxtg-v1.2”.

Be certain to review and follow the configuration notes in the README. Then, you’re ready to fire it up!

BMXTG 1.2 Released

The Brandmeister XTG Dialer (BMXTG) has been updated to version 1.2. Enhancements include automatic download of the masters address list and automatic download of talkgroup IDs and labels. Any talkgroup label may be changed through use of the talkgroups.conf file. Be sure to review the README file for changes.

DV4mini control panel in the background with the Brandmeister XTG Dialer in the foreground.

The changes will make BMXTG easier to configure and the user no longer needs to be concerned about IP address changes of the BM servers. A simple stop and start of the program will refresh the server list and talkgroup list automatically.

I’ve also updated the DV4mini Raspberry Pi 2/3 image to include BMXTG v1.2.

BMXTG is licensed under the Creative Commons Attribution + Noncommercial 3.0 License. Attribution Required / Noncommercial use permitted.

Tracking North Korean Numbers

My Aussie mate, Mark Fahey, has spent a number of years studying the Democratic People’s Republic of Korea.  He passes on the following information about North Korean “spy numbers” stations:

“The Pyongyang numbers (designated V15) have either become less regular or changed their schedule since March. Its been a few months since I have personally received them – but I also haven’t been specifically tuning in for them lately so maybe I have simply missed noticing a timing change.

“If you want to find the North Korean numbers, they are read out in a block between songs within the regular programing of the Pyongyang Pangsong radio station. The choice of music immediately before the number block seems to indicate which recipient agent the transmission is directed to. For Agent 27 “We Will Go Together with a Song Of Joy” is played, whereas Agent 21’s song is “Spring of my Hometown.”

“The announcements typically take between 5 to 10 minutes to read dependent on the number of digits passed. The transmission schedule is variable; in early 2017 the broadcast alternated with a cycle of one week on Thursday night at 12:45AM Pyongyang Time (1615 UTC) and the following week on Saturday night at 11:45PM Pyongyang Time (1515 UTC).

“Pyongyang Pangsong can be heard on these shortwave band frequencies (it is also on MF & FM on the Korean peninsular):

3250 kHz Pyongyang 100KW Transmitter
3320 kHz, Pyongyang 50KW Transmitter
6400 kHa Kanggye 50KW Transmitter”

If you’re interested in learning about what life is like “Behind the Curtain“, Mark has compiled a detailed multimedia publication based upon his actual observations inside North Korea.  It is available at no cost via iTunes.

Monitoring NextGen ATC (on the cheap!)

A key component of next generation air traffic control is Automatic Dependent Surveillance – Broadcast (ADS-B). The current FAA mandate is for all included aircraft to output ADB-B transmissions no later than January 1, 2020. But you don’t have to wait to receive and map ADS-B. There is a lot of air traffic to be seen.

dump1090 as viewed via a remote web browser.

Some folks are using complete downloadable images that are set up to feed flight tracking services such as FlightAware. If you’re interested in doing this, The SWLing Post recently featured an article that you’ll enjoy. I wanted to explore whether I could use some items already on hand to see a map of overhead aircraft on any computer on my home network.

I pulled out an older Raspberry Pi Model B and a 4 GB SD-Card and installed a copy of Raspbian Jessie Lite. The Model B has been retroactively called a Raspberry Pi 1 Model B. It is equipped with 512 MB of RAM, two USB ports and a 100mb Ethernet port.

I decided to use a spare older RTL-SDR stick based on the RTL2832U and R820T chips. This USB device comes with a small antenna that I hoped would be good enough to get me started. It is not in any way optimized for the 1090 MHz signals that are used by ADS-B and is roughly 19 parts per million (ppm) off frequency. It cost a bit over $10 at a hamfest a couple of years ago. The designs have improved since the early models were offered. Newer models include a TCXO (thermally compensated crystal oscillator) for stability and accuracy.

I needed software to take signals from the RTL-SDR stick and plot them on a map. That software is “dump1090”, originally written by Salvatore Sanfilippo. I added an install stanza to the Makefile, along with a systemd service file, for a smooth system install. I also needed to install the RTL-SDR USB drivers. The complete installation runs “headless”, meaning no monitor, keyboard or mouse need be connected. Remote management can be done via ssh.

First, bring the Raspbian Jessie installation up to date.

sudo apt-get update
sudo apt-get upgrade

Add some needed packages.

sudo apt-get install git cmake libusb-1.0-0-dev

Compile and install RTL-SDR drivers.

git clone git://git.osmocom.org/rtl-sdr.git
cd rtl-sdr
mkdir build
cd build
cmake ../ -DINSTALL_UDEV_RULES=ON
make
sudo make install
cd ~
sudo cp ./rtl-sdr/rtl-sdr.rules /etc/udev/rules.d/

Prevent native DVB-T drivers from loading.

cd /etc/modprobe.d
sudo vi blacklist.conf

Add blacklist dvb_usb_rtl28xxu to the file and save. You may now reboot. After the system comes back online, plug in your RTL-SDR device and the driver should load. You may test by running rtl_test -t. If the device is properly seen by the driver you should see the following:

Found 1 device(s):
  0:  Realtek, RTL2838UHIDIR, SN: 00000001

Using device 0: Generic RTL2832U OEM
Found Rafael Micro R820T tuner
Supported gain values (29): 0.0 0.9 1.4 2.7 3.7 7.7 8.7 12.5 14.4 15.7 16.6 19.7 20.7 22.9 25.4 28.0 29.7 32.8 33.8 36.4 37.2 38.6 40.2 42.1 43.4 43.9 44.5 48.0 49.6 
[R82XX] PLL not locked!
Sampling at 2048000 S/s.
No E4000 tuner found, aborting.

Don’t be concerned by the “No E4000 tuner found” message. The E4000 is an older chipset that is no longer used by today’s RTL-SDR devices.

Compile and install the dump1090 code.

https://github.com/K2DLS/dump1090.git
cd dump1090
make
sudo make install
sudo systemctl daemon-reload

Configure dump1090 options.

cd /etc/default
sudo vi dump1090

Here’s what I placed in the file.

# Default settings for dump1090.
DUMP1090_OPTS="--quiet --net --lat xx.xxxxx --lon -yy.yyyyy --ppm 19 --gain -10"

–quiet runs in the background
–net starts a webserver so that you can access via a web browser
–lat set to YOUR decimal latitude (negative for South)
–lon set to YOUR decimal latitude (negative for West)
–ppm if you know the ppm tolerance of your device (otherwise omit)
–gain -10 which sets gain automatically

A full parameter list can be reviewed by typing dump1090 --help.

With an antenna connected you can perform a quick device check by typing dump1090 --interactive. If all is well you’ll see a screen like this:

Hex     Mode  Sqwk  Flight   Alt    Spd  Hdg    Lat      Long   Sig  Msgs   Ti/
-------------------------------------------------------------------------------
A39D11  S                                                         6     1    4
A25D36  S                     1775                                7     4    3
AAA593  S                     2575  205  075                      7     2    7
A25238  S                                                         4     1   12
A0480B  S                    19650                                8    28    3
ACF4DD  S                     3825                                7     2   14
A41F61  S           FDX3018   2800  211  025   40.428  -74.332   23    83    0
A6FFFE  S     1753  LXJ550   30475  371  226                      8    63    0
C060B3  S                     4625                                6    14    1
ACF69B  S                    23250                                6    25    1
A2D27C  S                    24000                               13    42    2
A0BF90  S                     9500  249  257                      5     3    9
A7D30A  S                    40000                                8   111    1
AE0192  S           SPAR958  32675                               22    93    0
ACC040  S                     7825                                8   146    2
ACA5DF  S                    26600                                6    79    0
A80C7B  S                     4550                                9   108    1
A7CC00  S                     7825                               35   123    0
ACF841  S     1507           14425                               50   132    0
A8C802  S           NKS149   23575  332  216   39.995  -74.262   12   160    0
A61949  S           UAL1105   2725                               14    60    0
AC2E20  S     1006           19925                               22   130    0
AB766A  S           DAL1526   8525  216  038   40.444  -74.213   81   249    0
AA4440  S                     5400  253  066                      6     6   13

Control-C exits this screen.

Now start the dump1090.service.

sudo systemctl start dump1090.service

If all goes well, a netstat -an will show that there is a binding to port 8080.

tcp        0      0 0.0.0.0:8080            0.0.0.0:*               LISTEN

Now you can start up a web browser from any computer on your home network and see a map of planes overhead. If your router supports internal dynamic DNS you can name the RPi and access via something like http://skynet:8080. Alternatively, use the IP address, which can be obtained via ifconfig.

eth0      Link encap:Ethernet  HWaddr b8:27:eb:12:34:56  
          inet addr:192.168.1.123 Bcast:192.168.1.255  Mask:255.255.255.0
          inet6 addr: fe80::1234:5678:8765:abcd/64 Scope:Link
          inet6 addr: fd68:bee:1f21:2221::5/128 Scope:Global
          inet6 addr: fd68:bee:1f21:2221:1234:5678:8765/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:990830 errors:0 dropped:418120 overruns:0 frame:0
          TX packets:323700 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000 
          RX bytes:87491798 (83.4 MiB)  TX bytes:207659746 (198.0 MiB)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

In this case, the URL would be http://192.168.1.123:8080.

Once the map appears, re-position it to your part of the world and enjoy learning about what is flying overhead. You can enhance your enjoyment by listening to your closest airport tower or air traffic control frequencies on a scanner. These transmissions use amplitude modulation (AM) and can be monitored an another RTL-SDR stick or a scanner, even a relatively old model.

New Raspberry Pi 2/3 DV4mini Image

The DV4mini software developers have been hard at work fixing bugs, especially with DMR, and making things work better. So, I thought it time to create a new DV4mini RPi image for your enjoyment. I first built my own image last year when I wanted to have turnkey vnc access to my DV4mini/RPi system.

This build no longer contains the unsupported DV4MF2 software. Rather, it has the most recent version of the DV4mini dashboard (201.77), the updated dv_serial (20170106) and my add on Brandmeister XTG Dialer. If you haven’t used the XTG dialer before, you’re in for a treat. It works great with a touchscreen display, but just fine with a keyboard and a mouse too. You might need to edit a couple of text files to set it up to your liking. For details, see /opt/dv4mini/bmxtg/README once you have the distro up and running.

Important default password info follows.

root / raspberry
pi / dv4m

vncviewer – dv4m

You SHOULD change the default passwords after you get things going. The standard unix passwd command is used to change the root and pi passwords. To change the vnc password, use x11vnc -storepasswd.

RTL-SDR on the Cheap SWL Fest Links

As promised during Thursday afternoon’s presentation at the SWL Fest, here are the links for RTL software and info mentioned. If you attended the presentation, I hope that you enjoyed it and found it useful.

SDR#, a flexible SDR app for Windows with MANY plugins
DSD+, decodes P25, DMR, Fusion, DStar (data only), and others
Virtual Audio Cable, a virtual patch cable to send the output of one program into the input of another
Unitrunker, analog and digital trunk tracker with lots of data decoding
HDSDR, a software radio that can also make use of the RTL-SDR hardware
Linrad, for those who prefer to work in a Linux or Mac environment
DAB Player, requires the original (not Zadig WinUSB drivers

The Big List of RTL Supported Software
RTL-SDR.ru, in Russian, but Google Translate is your friend.

Update: I have added the video narratives as a YouTube playlist.

Correction: During the talk I stated that I thought the MCX connector used on the earlier DVB-T dongles appeared to be the same as the connector used on some Sirius satellite receivers.  I just took a close look and realized that while they are somewhat similar in appearance, the Sirius connector is larger and is actually an SMB connector.