Black Cat Systems


Follow our tweets!

Home
Lost Reg Code?
News
Online KiwiSDRs
macOS Software
Windows Software
Ham Radio iPhone/iPad
Linux Software
Support/FAQ
Update Policy

USB Icom CI-V Interface

Radio Hobbyist Products

  22m Programmable Beacon Kit
  22m Part 15 Beacon Kit
  CW Keyer For Beacons Kit
  Jellyfish Transformer
  Cyclops Antenna Transformer

General Interest Programs

  Atomic Mac/PC
  Audiocorder
  Audio Toolbox
  Black Cat Timer
  Diet Sleuth
  iUnit
  Graffikon
  Graph Paper Maker
  Health Tracker
  Image Resizer
  Knitting Wizard
  Label Wizard
  Prog Audio Gen
  Sound Byte
  Synth 76477

Amateur Radio Programs
  AirSpyHF+ Server
  Audiocorder
  Black Cat Absolute ACARS
  Black Cat ACARS
  Black Cat ALE
  Black Cat ALE Vacuum Cleaner
  Black Cat NetFinder
  Black Cat GMDSS
  Black Cat HF Fax
  Black Cat SSTV
  Black Cat NAVTEX SITOR-B
  Carrier Sleuth
  Cocoa 1090
  Cocoa RTL Server
  DGPS Decoding
  DX Toolbox
  Elmer
  MatchMaker
  KiwiKonnect
  KiwiSDR Monitor
  KiwiSDR Sound Client
  MININEC Pro
  Morse Mania
  MultiMode
  sdrRewind
  RF Toolbox
  SDRuno Plugin
  SDRuno Equalizer Plugin
  SelCall
  Sonde

iPhone/iPad Apps
  ALE
  Atoms To Go
  dB Calc
  Clik Trak
  DGPS Decoder
  Drill Calc
  DX Toolbox
  Elmer Extra
  Elmer General
  Elmer Tech
  Feld Hellschreiber
  Field Strength Calc
  Function Generator Pad
  GMDSS
  Godafoss
  HF Weather Fax
  iAttenuate
  iFunctionGenerator
  iSoundex
  iSoundByte
  iSweep
  iUnit
  Morse Mania
  ACARS Pad
  Morse Pad
  NAVTEX Pad
  Packet Pad
  PSK31 Pad
  SSTV Pad
  Photon Calc
  Rad Map Tracker
  RF Link Calc
  SelCall Tone Gen
  Sound Byte
  Sound Byte Control
  Spectrum Pad
  SWBC Schedules
  Synth 76477
  Synth Motion
  Transmission Line Calc
  Weather Calc
  Wire Calc

iPhone/iPad Bundles
  RF Calculator Apps
  Ham Radio Decoder Apps
  Audio Utility Apps
  Shortwave Weather Apps
  Ham Radio Exam Study Apps
  Shortwave Decoder Apps

About Black Cat Systems
Site Map
Our software for Mac OSX
Privacy Policy
Press/Media
HFunderground
Apple /// Emulator

Macintosh Links
Shortwave Radio
Pirate Radio
Spy Numbers Stations
Science and Electronics
Ham Radio Software


   

DGPS Decoder

Available in Android Market

Android App to Decode DGPS Transmssions

(Also available for the iPhone/iPad/iPod Touch)

This app can decode DGPS (Differential Global Positioning System) beacon transmissions. DGPS stations transmit the difference between positions indicated by GPS satellite systems and the known fixed position of the station. This allows higher accuracy. DGPS transmissions are 100 or 200 baud and are transmitted on frequencies from 285 kHz to 325 kHz. Hundreds of these stations are operated by the Coast Guard and other agencies, and they can be interesting DX targets.

To use this app, you need a radio that can tune the correct frequency range, either in SSB or CW mode. Most "shortwave radios" can do this. Ideally you use a cable to feed the audio from your radio into your device, but you can also place the radio speaker near your device's microphone, or even better yet, plug earphones into the radio, and place them next to the device's microphone. You may need to experiment to get the best quality audio pickup, without any outside noise or distortion.

To decode the transmission, tune your radio to a DGPS frequency. You can either tune directly to the frequency in CW mode, in which case you set the center frequency in this app to frequency of the tone produced by your radio in CW mode, usually close to 800 Hz, or use USB mode, tune 1 kHz low, and set the center frequency in this app to 1000 Hz.

To assist with practice in setting up the app to decode transmissions, you may wish to first try decoding this recorded DGPS station, set the app for 200 baud and a center frequency of 1000 Hz: http://www.blackcatsystems.com/ipad/DGPS.WAV

The app displays an audio spectrum signal plot, the green bars on a black background. Also on this plot, the baud rate and center frequency are displayed on the left and right sides, respectively. Above this, there are several buttons. You've likely already figured out that the Help button brings up these instructions. Next to that is the baud rate button, tapping it toggles between 100 and 200 baud. Next to that are the - and + buttons, they change the center frequency. Finally there is a volume indicator. Ideally the input volume should be between about half way and three quarters. You can also change the baud rate by double tapping on the spectrum, and adjust the center frequency by swiping left and right.

When you want to decode a DGPS transmission, select the baud rate, and feed audio into your device. If you don't know the baud rate, try one speed, then the other. 100 baud transmissions have a more narrow bandwidth than 200 baud, eventually you can learn which is which by observing the spectrum display.

Eventually, if you have tuned into a DGPS transmission that is strong enough, you will start seeing decode messages printed.

A typical decoded message looks like this:

[23:24:00 08/08/16] 806 12 13 289.0 kHz Driver, VA United States 36.9633 -76.5622 306.61 km 172.711 deg
First the current UTC date and time are printed in brackets.

Then the station ID, 806 in this case, as well as the two reference IDs, 12 and 13 in this case.

That is followed by the assigned frequency, 289.0 kHz for this station. You can compare this value to what your radio is tuned to, they should match. If they don't, then ignore this message, as it was incorrectly received. With weak signals, it is common to receive incorrect messages, because static or other interference has corrupted some of the bits. Just ignore them.

The location of the station is then displayed, the city, state, and country, followed by the station location.

Then the distance and bearing to the station is displayed, providing you have correctly set your location in the app.

Note: for devices that don't have dedicated home/menu buttons on their device, holding down the 'return/exit' button is the alternate way to access the application menu.


Email your comments and questions to support@blackcatsystems.com

Last modified August 12, 2016