Category Archives: Archive

NBEMS – Doing It The Ham Radio Way

Archived from: uspacket [dot] org/network/index.php?topic=44.0

Archive reason: domain expired, server shutdown, or otherwise unaccessible.

Notes: Some reformatting applied.

I do not take any credit for the content or make any claim of accuracy.

NBEMS – Doing It The Ham Radio Way
by Charles Brabham, N5PVL
Updated 06-27-2012

NBEMS ( Narrow-Band Emergency Message System ) is perhaps the best solution available for moving eMail and other text-based information over amateur radio frequencies, to handle emergency communications. Here I will outline the reasons that I have come to this conclusion after reviewing the available amateur radio messaging systems.

Mission Parameters:

Our mission is simple. – To provide an alternate means of moving messages into and out of a disaster area where regular internet access has become compromised, is limited or nonexistent. For this purpose, it is seldom necessary to transport messages or eMail via amateur radio any farther than 100 miles or so, or to move any great volume of data. It is important however that the messages get through with 100% accuracy, and in a timely manner. In most cases, this service will be needed for anywhere from a few hours up to several days.

Considerations for Amateur Radio Operators:

For amateur radio operators, the best method is to utilize the radios, software and equipment that we use every day for ham radio, and so are already familiar and comfortable with. The system should be inexpensive and easy to use so that all amateurs may participate, and are not faced with a steep learning curve in order to be ready to act in an emergency. Extensive training and drilling should not be required in order for hams to function well when needed. There also should be some flexibility to handle different needs of unexpected situations that may be encountered. The system should work independently of existing infrastructure, and require no costly and complicated infrastructure of its own.


I have reviewed the amateur radio eMail and messaging systems in current use, and have found that NBEMS best covers the mission parameters and the considerations for amateur radio operators outlined above.

NBEMS was developed as a collaborative effort between Dave Freese W1HKJ and Skip Teller KH6TY, the developer of the popular DIGIPAN PSK31 software. It consists of a suite of programs that send text, images and eMail files error-free. The two main programs, FLDIGI and FLARQ are designed to run under Linux, Free-BSD, Mac OS, Windows XP, Win2000, Vista and Windows7.

The NBEMS system is designed to operate on all amateur bands, but is optimized for short to medium range communications such as SSB VHF, or HF with an NVIS antenna can provide. It can also be utilized on VHF FM, and even operated through a FM voice repeater at need.

Digital modes currently recommended for HF NBEMS operations are: OLIVIA 8/500, OLIVIA 16/500, MT63 1k, PSK-125R and PSK-250R. For VHF use on simplex or through a repeater, MT63 2k is recommended and can be used to good effect without a soundcard interface.

The free FLDIGI multimode soundcard software offers many digital modes, but the modes listed above are most often associated with NBEMS. Amateurs who use FLDIGI for everyday QSOs in PSK31, Hell, Olivia, MT63 etc. will be familiar with the software when occasion calls for the NBEMS system to be called up.

An optional part of NBEMS is the FLARQ software, which provides the interface to your eMail program, and which also provides the ARQ feature for NBEMS which gives you 100% accurate transmissions of the messages and images you transmit. In addition to email, you can send comma delimited spread sheets/data bases, text, and many ICS form-based messages.

The FLWRAP add-on program allows you to transmit a bulletin to an unlimited number of stations simultaneously. Each recipient can confirm individually whether they have received the data with 100% accuracy, as FLWRAP generates a checksum for each message.

The FLMSG program makes authoring, sending and receiving text, ICS-205, ICS-206, ICS-213, ICS-214, and ICS-216 forms in addition to ARRL Radiograms a simple point and click proposition.

NBEMS Features:

  • Inexpensive ( free soundcard software )
  • Simple to use, reducing training requirements
  • Effective, perfectly tailored to the EMS mission
  • Narrowband modes conserve spectrum
  • A live operator on each end, eliminating interference potential
  • Flexible enough for use with most equipment under most conditions
  • The software is great for everyday use, again reducing training requirements
  • Specialized add-on software for net control, rig control, callbook data, logging etc. are available

To learn more about NBEMS and to download the software:

Basic information and software download:

NBEMS info and a downloadable PowerPoint presentation:

ARRL articles about NBEMS:

Informative Weblog article about NBEMS:

NBEMS/FLDIGI Sound Card Calibration

9/26/2017 update: This is a less effective way of calibrating Fldigi.

The officially recommended calibration method is to use a time standard such as WWV and WWVB.  Details are in the Fldigi manual.

I’ll update or create a post as time permits with more details.  This post and instructions below will be left for reference and should be considered archived.

Archived from: pa-sitrep [dot] com

Archive reason: domain expired, server shutdown, or otherwise unaccessible.

Notes: I had a copy of both the program and the text, I am re-posting both.  Unfortunately it only is available for Windows.

Check the Fldigi tag for my posts running it on the Raspberry Pi or how to use Fldigi.

If you’re concerned about downloading the exe, it was analyzed by VirusTotal and showed 0 detections. The hashes are below and the SHA256 can be compared against the VirusTotal link.







I do not take any credit for the content or make any claim of accuracy.

1) Download and save CheckSR.exe to your desktop. This is a small, standalone, application that consist of a single exe file. When you double click on it, once it’s saved to your desktop, it provides the capability of analyzing your sound card offsets and gives you the corrections in parts per million (ppm):


2) Open NBEMS/FLDIGI, go to configure, defaults, sound card, audio devices tab and make sure you have the sound card you use for your interface properly selected from the capture and playback drop down choices. Then click the audio settings tab.


3) Under the audio settings tab, you should see a sample rate drop down box for capture and playback. Under each drop down box, select the sample rate that has (native) listed after it and take note of this figure. Click save config, then click save. Close FLDIGI.

Note: the ‘capture’ sample rate is the only one that seems to have the ‘native’ designation. The playback and capture should be the same.


4) Going back to CheckSR, open the application (if it’s not already open, double click on the desktop icon now) and from the drop down boxes for sound card settings, Input and Output, choose the sound card you are using with FLDIGI. Next, select the sample rate from the drop down box in CheckSR for the sample rate that FLDIGI showed as “Native” then click start.


5) Let the application run for about 15-20 minutes. You will notice that the numbers will progressively stabilize. After about 15-20 minutes, click stop then write down the resulting figures on input and output for the measurements in Hz and PPM. Keep this record.


6) Open FLDIGI, go to configure, defaults, sound card and click on the audio settings tab. Enter the PPM figures for RX ppm (CheckSR ppm Input figure) and TX ppm (CheckSR ppm Output figure). If you had a figure that resulted in a minus from CheckSR, enter the PPM setting with the minus symbol followed directly by the figure with no space. Then click save config, then close.

Although this procedure does not seem to be necessary for MT63 2k long on FM, it is advisable that anyone using FLDIGI, regardless of modes used, should perform this procedure immediately following setup. Once these calibrations are applied to the software, no changes should ever have to be made again, unless you change your software to radio interface sound card.