Advanced Prepper Communications- Beyond the Basics | AMRRON ADVANCED PREPPER COMMUNICATIONS- BEYOND THE BASICS What’s all this about PSK31, MT63, FEC, NBEMS and NVIS? By Engineer Paul Synopsis In this article we take a quick look at PSK31 and MT63, two popular digital communications modes and what role each is best suited for with respect to emergency communications. Next, a short intro to ARRL’s NBEMS (Narrow Band Emergency Messaging Software) which features fldigi. We also touch on NVIS, FEC and a few other acronyms related to digital, emergency and disaster communications. In a world of ever-advancing technology, our reliance on that technology for something as fundamental as communications leaves us all vulnerable should that technology fail us. As an illustration, we recently experienced county-wide communications failure when the main fiber-optic communications cable in our valley was severed during construction. Internet as well as land-line and cellular telephones went down. Until the line was bypassed and repaired, the only reliable form of communication was radio. Fortunately there were no emergencies during this time of vulnerability. It’s hard to imagine life without telephones and Internet until it happens. In times such as our local communications failure, or a man-caused or natural disaster, amateur radio may provide the only means of civilian communication. Getting information into, out of, and throughout an affected area is vital. Voice communication works, but if available, digital communications provide a much faster and error resistant method for passing message traffic. Granted, amateur radio digital communication relies on modern technology and is subject to its own failures. A solar flare or EMP could fry our computers and modern radios, but many hams have backup laptops and radios stored in Faraday cages. Though there is the possibility of such an event, the probability is much lower than other scenarios that lead to the loss of communications infrastructure, so prioritize your contingencies. Digital Modes Probably the most widely used digital mode (outside of Morse code) is PSK31. PSK31 (Phase Shift Keying, 31 baud) is a wonderfully efficient conversational digital mode – good for typing back and forth. PSK31 clocks in at about 50 Words Per Minute (wpm) and uses about 31Hz of bandwidth. It lacks error detection and correction, but that’s not usually necessary for a one-to-one conversation where the operator at the receiving station can simply type back “What did you just say?” if something gets garbled. This interaction is the human form of an error detection and correction protocol. You can have the computer take care of error detection and retransmission for you. This is what ARQ protocols do: Automatically ReQuest retransmissions when necessary. This is fine for one station sending to a single receiving station, but when a station is sending a message to multiple recipients, it becomes impossible to manage multiple stations requesting retransmissions. Enough said about ARQ. Let’s now look at FEC or Forward Error Correction, a fancy name for a simple concept. Simply send more than one copy of the information. Now, to make it more robust, let’s spread the data around in time and frequency so that no fading or noise bursts can corrupt all copies of that redundant data. MT63 (Multi Tone 63) does this. MT63-1000, for example uses 64 tones (numbered 0 to 63) spaced 15.625Hz apart, using 1kHz of bandwidth. That’s 64 parallel data streams on which to encode multiple copies of the data! MT63-1000 provides 100wpm throughput. MT63 is a remarkably robust signaling mode in noisy conditions. Its encoding and FEC do much to ensure that a station receiving an MT63 message will have enough information to reconstitute the original message. This allows a sending station to “broadcast” a digital message to any and all stations that care to receive it and know that in all likelihood it will arrive error free. That’s something not possible with PSK31, nor practical with most other FEC modes.