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Difference between revisions of "DXing Digital Utilities"

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* [http://www.bcar.us/digsig.htm Digital Signal Audio Reference]
 
* [http://www.bcar.us/digsig.htm Digital Signal Audio Reference]
 
* [http://det.bi.ehu.es/~jtpjatae/sound.html Eduardo Jacob's Home Page- Sound Files]
 
* [http://det.bi.ehu.es/~jtpjatae/sound.html Eduardo Jacob's Home Page- Sound Files]
* [http://www.w1hkj.com/FldigiHelp-3.21/Modes/index.htm fldigi samples of decodeable modes]
 
 
* [http://hfradio.org.uk/html/digital_modes.html G4UCJ's Radio Website]
 
* [http://hfradio.org.uk/html/digital_modes.html G4UCJ's Radio Website]
 
* [http://sferix.myweb.hinet.net/hfasia/ HF Asia Sound Files]  
 
* [http://sferix.myweb.hinet.net/hfasia/ HF Asia Sound Files]  
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* [http://wb8nut.com/digital/ WB8NUT Digital Information Page]
 
* [http://wb8nut.com/digital/ WB8NUT Digital Information Page]
 
* [http://www.qsl.net/zl1bpu/ ZL1BPU Fuzzy Modes]
 
* [http://www.qsl.net/zl1bpu/ ZL1BPU Fuzzy Modes]
 
 
  
 
==Testing Your New Setup==
 
==Testing Your New Setup==

Revision as of 20:54, 12 November 2014

Equipment and Connections

If you decide to get into digital, you will need better equipment than a simple portable. While some portables will work with reasonably stronger signals, the more complex the signal (or conditions), the more a portable will fall short. Tuning accuracy, selectivity, stability and even mode selection play a significant role in being able to correctly tune a signal.


While the number of newer desktop receivers has plummeted, a sharp eyed listener can often find such receivers at hamfests. Do your homework - use the Receiver Reviews article to begin your research. Even though most of the reviews do not specifically refer to digital capabilities, keep an eye on some of the characteristics mentioned earlier. Those folks with a modern ham transceiver have an advantage - they often have a general coverage receiver built in.


In the case of connecting a receiver to the PC soundcard, a clean connection is a must. This article from our wiki describes some pitfalls and solutions. It's strongly encouraged to make the connection with shielded audio cable to restrict the possibility of stray noise pickup. However, you will need to experiment with the soundcard settings on the PC to see which works for you. There's no way to present a guide for each and every instance, as there is wide variation in models and quality, depending on the soundcard installed on the PC.


The big push these days is in the development of Software Defined Radios (SDRs). Many are very capable at HF; one of their biggest advantages is being able to see a large swath of frequencies, all at one time. For modes like ALE, which show up for a few seconds and are sometimes gone, this is a big plus for capturing data quickly. See our Software Defined Radios article for numerous reviews and other technical information on this subject.


Connecting a PC soundcard to your SDR may require the use of some Dynamic Link Libraries (DLLs) that must be installed. With others you can use software like Virtual Audio Cable (VAC) to route the audio from the SDR to the PC. Those packages that can directly interface with SDRs are shown in green on the Utility Monitoring Central website.


What about software?

  • The Utility Monitoring Central website lists packages for PCs, Macs and even a few for Ipads. Some are free, some not.
  • Marius Rensen's popular HF FAX site has more information on FAX software and schedules


Why cant I decode this signal?

Let's be clear at the outset - there are many digital signals that will never be decoded. Unlike digital signals in the amateur radio service, there are many that are encrypted to prevent casual viewing. Most are assumed to be military in nature. The challenge is to find signals that can be decoded, or at least identified.


What are all those strange sounds?

The first task is to properly identify the mode. There are numerous digital modes, and a casual examination of the Utility DXers Forum on Yahoo groups would turn these up.


  • ALE. This mode is often used to test the propagation path between 2 stations, and to sometimes pass short messages. The link provides more information on this mode as well as compatible software. Note that this one of the newer modes that hams, as well as non-hams, utilize.


  • Digital Selective Calling (DSC). This website has a great deal of information, as well as links to software that can read this mode.


  • FAX (Facsimile) - Most often used for weather charts, and on rare occasions, news items. Happily this is one mode that is easy to both recognize and decode.


  • HF Datalink (HFDL), also known as HF ACARS. See the linked article for more information.



  • SITOR-B - Also known as AMTOR Mode B, FEC or NAVTEX, this mode is often used for maritime weather and warnings from various organizations. This website also has a great deal of information on this mode. While not used by the amateur community much anymore, it still enjoys wide popularity in the maritime community.


  • STANAG 4285 - Most often used by the French and NATO forces. See this article (PDF) from the Utility DXers Forum homepage on identifying and decoding this mode. Often the traffic is encrypted, but the IDs are not, making it easy to at least identify the users. Occasionally you will get lucky and catch the stations running test loops (in French: Voyez Le Brick) which identifies the station.


While there are many digital signals that are easy to identify, many are not. There are just as many modes that most people have never heard of. This article (PDF) is a list of those modes that have been identified, but there are likely more that have never been identified or classified. It's quite possible that these modes are military in nature. These modes could be encrypted and very difficult, if not outright impossible, to read.


So how can we identify the users of these modes?

In some cases, the frequencies used by these modes are well known and widely published (such as HFDL). This is, of course, but one clue in identifying a user. We need another tool to help narrow the field.


Some older modems and TNCs (for example the Universal M-7000) had the ability to attempt to guess what mode a particular signal was sending (some very expensive soundcard decoders also have this ability). Unfortunatly these classifiers can be fooled by a poor signal level or noise - so it's not always the best choice for determining the mode of a signal


Many digital decoding packages have the ability to display an audio representation of the signal being received. This ability comes by many names; sonogram, waterfall display or audio spectrum display, just to name a few. This article (PDF) describes in some detail how to use a sonogram and how to record the signal. Both are important - you may need to play the signal back several times before you get a clear picture of what the signal looks like. The accuracy of the sonogram is going to be greatly influences by many factors; the quality of the signal being received, your receiving setup and the PC you are using will all play a role here.


It should be noted that new modes show up from time to time that take considerable knowledge and skill to properly analyze.


Now what about identifying the patterns shown in the sonogram?


These links have pictures of sonograms (and in some cases audio samples) of numerous kinds of digital signals. You can use these as a guide, but remember, it's another clue as to the mode (and by extension, sometimes the potential user) of the signal

Testing Your New Setup

Instead of hunting for readable signals, check out the following links for schedules. Please read them carefully to see if the software you are using is compatible.


YouTube Videos


Are there other resources?

The RR forum for this article can be found here. In addition, this page at the Utility Monitoring Central website lists various mailing lists devoted to specific software packages. Go here for technical support for them first.


The Utility DXers Forum (UDXF) Yahoo group is an excellent place to help identify the mode and user of a particular signal. There are also specialized Yahoo groups (such as the one for HFDL) that can supply updated software or active frequencies. There are also ircchat sites (see irc://irc.starchat.net/wunclub ) where you can ask questions, and get nearly immediate responses. These are often your best sources of information.