Donnerstag, 18. September 2014

AP510 / AVRT5 APRS tracker - HF signal

AVRT5 APRS tracker
With the help of one of my colleagues @ QRL we measured the HF signal (144.800MHz - European APRS QRG) of the AVRT5 APRS tracker with a R&S Spectrum analyzer (3kHz-7GHz).
All measurements were made with a 6dB attenuator and 1m RG58CU between the Tracker and the Analyzer.

HF Signal - 144.800MHz

Power Measuring: 30.46dBm / 1.1Watt

At -5khz from center freq we measured a delta of 41.18dB

Harmonic frequ: The 1st harmonic at 289.7MHz has a delta of -9.13dB. That is too high for using it for a permanent digi. A filter is needed to further lower the harmonic signal.

AFSK data signal burst (my beacon of DK7XE-8) ~1sec duration

AFSK data signal - last 320ms

Dienstag, 16. September 2014

Linux - downloading a MP3 file and converting to WAV if file has changed

For our local FM-repeater DB0HHW i wrote a script that downloads the weekly DARC broadcast / "Deutschlandrundspruch" and converts it into WAV audio whenever the file has been changed. The file can be played on demand via the repeater DB0HHW (svxlink tcl routine).
The script is executed by cron every 15min.
The download from the i-net is done with wget. The -N flag forces
wget to download only if the source file on the i-net is newer than the local copy.
The conversion from MP3 to WAV (the repeater software svxlink can only play WAV) is done with lame. The - freeformat -b 16 flags allows to create bitrate of 16kbps (again a svxlink requirement).
Finally the converted audio file is moved into the svxlink audio directory.

# variable definitions
# web source of the dl-rundspruch mp3 file
# filename of the dl-rundspruch mp3 / wav file (prefix need to be the same)
# local directory where the mp3 file is downloaded to
# check-file that holds the lates status after mp3 file has changed
# svxlink audio directory and filename. place where wav-file will finally be stored

# touch the check-file to make sure it exists

# change into the local download directory and
# start download of dlrs file only if new version is available
wget -q -t 5 -nd -N $DLRS_SRC_DIR/$DLRS_MP3_FILE

# check if there was a change on the mp3 file and convert to wav with
# lame if newer file available
# check if newer version is done by comparing the output of 'ls -l <mp3-file>'
# with the output of 'ls -l <mp3-file>' stored at last update into the check-file.
if [ "$(cat $LOCALDIR/$DLRS_CHECK_FILE)" = "$(ls -l $LOCALDIR/$DLRS_MP3_FILE)" ]; then
        echo "file is the same -> no conversion" > /dev/null;
#       echo "file has changed -> start conversion"
        # store output of 'ls -l <mp3-file>' into the check-file
        # convert mp3 into wav format with lame
        lame --decode --freeformat -b 16 $LOCALDIR/$DLRS_MP3_FILE;

#copy the wav audiofile to the svxlink audio directory if newer version exists

# --- DONE ---

73' Gerald
- dk7xe -

Montag, 8. September 2014

AP510 / AVRT5 APRS tracker

The AP510 / AVRT5 APRS tracker is a tiny APRS tracker with built in GPS and bluetooth.
Transmitting power is around 1W (detailed measurement result available on ap510-avrt5-aprs-tracker-hf-signal).

The official website is (chinese) / webshop at but there is an english group on Yahoo
You will find the latest firmware / configuration software there as well.

For the German's: Klaus, DJ7OO hat einen Erfahrungsbericht auf seiner Homepage.

I got mine from a Taiwanese Hamradio friend while being there on a business trip in June 2014.

Some details

  • Transmission can be set to a fixed timing, smart beaconing or triggered manually via button.
  • Built in GPS.
  • Acts as a WIDE1-1 or WIDEn-n digipeater if needed.
  • Fixed position can be programmed (e.g if used as a fixed station).
  • Tracks can be stored on MicroSD card.
  • Built in Battery
  • Configuration / Charging to be done via serial connection (miniUSB connector).
  • KISS / Waipoint / UI frame output on serial (4800Bd) and Bluetooth.
  • Works perfectly with APRSdroid as BluetoothTNC (Output to be set to KISS).
  • Operating frequency can be set via configuration program.
  • Some parameters can be set via AT commends
I'm really happy with this device since it works perfectly with APRSdroid and fit's in every pocket.


  • Bluetooth connection only works after GPS lock therefore you have to wait some seconds before connecting to the device. Bluetooth pairing code is 1234.
  • miniUSB connector is a Serial Port therefore the included USB cable needs to be used for programming (charging works with every standard USB cable).
  • Help is provided via the AP510 / AVRT5 Yahoo Group.
  • Be aware that the TX power is low compared to other stations therefore not every transmission might reach a Digi/Gate when being in a busy APRS area.
  • If you have problems on connection via serial take a look at the Video on AP510 APRS tracker configure software and firmware

Serial / BT commands

According the info on some settings can be changed by sending AT commands.
Either you connect via the serial (USB) port with following settings 4800Bd 8N1. Or you use a bluetooth, e.g. BluetoothTerminal on Android.
Import: serial/bluetooth communication seems to work ONLY after GPS lock.

To make it work you have to follow the steps below
1) connect
2) send ^M
3) send the AT command. E.g. AT+BEEP=0
4) the device will send OK back.
5) reboot the device to have the NEW settings active.

The following commands are currently known

setting the callsign

setting frequency

switch tone on

switch tone off