Narrow Band Emergency Messaging System (NBEMS)

The Narrow Band Emergency Messaging System (NBEMS - pronounced "N-beams" in the trade) is a suite of software programs designed for point-to-point, fast, error-free, emergency messaging up to or over 100 miles distant, and takes up a very minimum of space on the ham bands.  The system is designed primarily for use on the two-meter band, or on HF with NVIS antennas, where there is a minimum of fading (QSB) to slow down message transfers.  Two meters has the advantage that distances long enough to span disaster areas of up to 100 miles can be dependably done with small, portable antennas.  In hilly regions, if two meters is not workable over the distances required, NVIS antennas on HF can be employed instead.

The system is comprised of a number of programs that work together:

      • fldigi / flarq - digital modem / ARQ file transfer
      • flwrap - file encapsulation / compression
      • flmsg - ARRL Radiogram & ICS213 message manager
      • flrig - rig control program, cooperates with fldigi

The computer soundcard is used as the modem, and other than a simple interface connection between the computer and transceiver, no additional hardware is needed.  Versions are available for a variety of operating systems, including Windows (XP or later), Mac OS X, Free-BSD, and Linux.  This software was reviewed by the ARRL in QST in 2007.
NBEMS & fldigi Program Home Page:  http://w1hkj.com/   and   http://www.w1hkj.com/NBEMS/
Beginner's Guide to fldigi:  http://www.w1hkj.com/beginners.html
Fldigi On-line Help Page:  http://www.w1hkj.com/FldigiHelp/index.html
Flarq On-line Help Page:  http://www.w1hkj.com/FlarqHelpFiles/flarq.html
A short article about NBEMS:  http://uspacket.org/network/index.php/topic,44.0.html
Step-by-step Setup & Configuration:  http://www.pa-sitrep.com/NBEMS/
NBEMS Yahoo Group:  http://groups.yahoo.com/group/NBEMSham/
Fldigi Wiki:  https://fedorahosted.org/fldigi/wiki
ARRL NBEMS Presentations:  http://www.arrl.org/nbems/


fldigi is a soundcard-based digital modem program.  Here is a list of the modes it supports:

      • CW
      • DominoEX 4/5/8/11/16/22
      • Feld-Hell, FSK-Hell, FSK-Hell 105
      • MFSK-8, MFSK-16, MFSK-16 pix
      • MT63-500, MT63-1000, MT63-2000
      • PSK/QPSK 31/63/125/250
      • Olivia (various tones and bandwidths)
      • RTTY (various baud rates, shifts, data bits, etc.)
      • Throb/ThrobX 1/2/4
      • Thor 4/5/8/11/22
      • WWV  (receive only - used to calibrate soundcard)
      • Freq Analysis  (receive only)


Lets suppose you want to send a critical message that must be received exactly as it was sent, or maybe you want to send a data file where it's highly unlikely that even a trained operator could tell that there was an error in receiving the data.  Or perhaps you need to broadcast a weather bulletin or situation report to multiple stations and allow each station to verify that the message was received exactly as it was sent.

Flwrap is an application that is designed to take care of each of these situations.  Flwrap allows you to transmit a text message, image, or binary file to either single or multiple stations and allow each receiving station to verify that the transmission was received without error.  In the discussion which follows the application name is Flwrap, the file encapsulation process is called wrap, wrapping and the encapsulated file is said to be wrapped.

The flwrap executable is a small desktop application that encapsulates a text file, an image file, or a binary file within a set of identifier blocks.  These blocks include a 16 bit checksum that is used to test the encapsulated file for integrity.  Flwrap is designed to be used to best advantage with fldigi but can be used with any digital modem program. Fldigi can recognize an wrapped transmission in the Rx data stream and automatically save the file.  Fldigi can process multiple wrapped files that are sent in rapid succession.  Fldigi does this without operator intervention. The conversion of files to and from the wrapped format do still require an operator.


fast light automatic repeat request is a file transfer application that is based on the ARQ specification developed by Paul Schmidt, K9PS.  It is capable of transmitting and receiving frames of ARQ data via either fldigi or MultiPsk on Windows, or fldigi on Linux.  The interaction between flarq and fldigi requires no operator intervention.  Program data exchange between flarq and fldigi is accomplished using a localhost socket interface.  The socket interface requires that one program act as the server and the other the client.  Flarq is a client program and fldigi is a server program.

Flarq can be used with the following digital modem as the transport layer:

      • BPSK all baud rates
      • QPSK all baud rates
      • MFSK all baud rates
      • DOMINOEX 11 or faster (do not use FEC)
      • THOR all baud rates, 11 or faster recommended
      • MT63 - all baud rates, flarq timing should be increased to accommodate mt63 latency

Please note that Olivia IS NOT compatible with flarq transmissions.  Olivia does not allow the transmission of the control codes required for flarq.


FLMSG is a simple forms management editor for the ARRL Radiogram and the NIMS ICS-213 message form.  Its data files are pure ASCII text that can be sent from point to point using the internet, amateur radio, or other electronic link.  The data files are designed to minimize the transfer size.  This is particularly important on amateur HF.  The data file and the transfer file are one in the same, but can be further encapsulated using either flarq or wrap for the purpose of confirming the received file integrity.


flrig is a transceiver control program designed to be used either stand alone or as an adjunct to fldigi.  The supported transceivers all have some degree of computer control.  The flrig user interface changes to accommodate the degree of computer control support available for the transceiver in use.