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HF Digital Decoding


Welcome to the HF Digital Decoding article. While tuning around the HF bands, you are very likely to hear a variety of squawks, beeps and other sounds that, at first, defy description. While noise sources are a likely source (typical of HF), at least some will be some sort of digital signal.


Let's be clear at the outset - there are many such signals that will never be decoded. Most are assumed to be military in nature. The challenge is to find signals that can be decoded, or at least identified.


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.


With propagation as lousy as it's been lately, a good antenna is an absolute must. The better the antenna the better the results will be, whether it's tuning digital signals or something else. See our HF Antennas article for more on this topic.


A critical part of any digital receiving station is a clean connection from the receiver to the PC. There are many ways to accomplish this without going through the expenditure of having a dedicated interface, although one is often used in the amateur service. Please see our Connecting Radios to Soundcards article for more information.

The RR forum for this article can be found here

Contents

Amateur Radio Digital

By far the easiest place to start in this field is the amateur service. But don't be fooled - although, by regulation, no digital mode can be uncopyable, specialized software will be required to decode them. See the software section on this article for more on this.

Audio Samples of Digital Signals

If you want to be able to identify a signal by sound, or by viewing it on a waterfall display (many digital decoding programs - and some soundcard programs - have this ability), then these sites are a good place to start

Modes and Links

  • ALE (Automatic Link Establishment - or by it's other name, MIL-STD-188-141A, as well as several variants)
    • The ALE page has a listing of all the packages that decode ALE.
    • The ALE Networks page consolidates a listing of active ALE networks.
  • HFDL misnamed HF Datalink, it's really an HF version of ACARS
  • What is Link-11?
  • The Maritime service utilizes Sitor-B from certain stations in the US, and FAX (Fascimile) is used for weather charts. The use of FAX for photo transmissions has been long gone, contrary to what you might read in certain ham equipment distributors and old websites. Satellites took over that function years ago.

Software

Slow Scan TV (SSTV)

YouTube Videos

Yahoo Groups and websites

Websites
Yahoo Groups

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