NBEMSNarrow Band Emergency Messaging System

W1HKJ – Dave, licensed for 52 yearsRetired USCG, MSEE, 40+ years in software dev.Expert in nothing, but works hard in digital mode code

M0GLD – Stelios, licensed 8 yearsMSCE, doctoral candidateExpert in cross platform development30+ years old

KH6TY – Skip, licensed 56 yearsElectronics entrepreneur – inventor of WX alert radioDeveloper of DigipanHuman interface design

WA5ZNU – Leigh, licensed since 1968 (7 years old)Expert in all things xml

F8CFE – StephaneOriginator and principal developer of hamlib

The Developers

W3NR – Ed, Extra ClassCW / RTTY & digital modes opRetired USPSNew Installs – RigCAT & Hamlib supportPatience of an angel – supporting users since version 1.0

WA4SXZ – Rich – licensed since 1965elmer for XP/Vista/Linux installations, esp' Yaesu rigs

KB3FXI – DaveNBEMS support

W3YJ – HarryNBEMS support

Many others who help in specific areas

The Support Team

NBEMSNarrow Band Emergency Messaging System

Is software

Fldigi – digital modem programFlarq – automated repeat request programWrap – file encapsulation program

Which Runs on - Xp

Lenovo Netbook

Which Runs on - Vista

Compaq Notebook

Which Runs on - Linux

Acer Aspire / Ubuntu 9.04

Which Runs on – Puppy Linux

Compaq Notebook – thumb drive boot

Which Runs on – OS X

Apple

Hardware•Windows, Linux or Mac OSX Computer

HardwareSound Card Interface & Transceiver

Sound Card Interface

•Connects computer sound card to the radio

•Provides RF isolation

•Provides ground loop isolation (transformer coupling)

•Can automate the PTT when you transmit.

HardwareSound Card Interface

SignaLink SL-1+ Geeks.com $5 USB audio-codec

A Homebrew Interface

For homebrewing, a blank PCB is available for $5.00 and a SASE

from Skip, KH6TY

Hardware•Windows, Linux or Mac OSX Computer•Transceiver•Sound Card Interface•Or, maybe just a $8 computer microphone

To start playing around... all you need is an inexpensive computer microphone! Just plug a mic into your sound card mic input and place the mic element somewhere near your radio speaker. Listen and

watch your display and practice differentiating the various modes.

Why Use Digital Modes

PSK-31 Olivia MFSK-16

Low Power - never need to run over 50 watts, 5 -30 watts is almost always sufficient Reliable communications – succeeds even when CW fails some modes work below -8 dB s/n Many modes - choose your mode depending on conditions Bottom of the solar cycle - works well, even under very poor conditions where phone QSO’s would be impossible! Emergency Communications You already have 99 % of the equipment – nothing expensive to buy It’s FUN

Digital Waterfall

time

frequency

Color == Amplitude•Blue = low amplitude•Yellow = medium amplitude•Red = high amplitude

Is a visual representation of time, frequency and amplitude

Recommended Digital Modes for EmComm with the NBEMS Software Suite

•DominoEX-11 – fast turn around time, good for moderate to severe HF conditions and non-mission critical messaging, impervious to transceiver tuning

•MFSK-16 – moderate speed, works under severe HF conditions, requires accurate and stable transceiver tuning.

•Olivia 16/500 – slow but very accurate under poor HF conditions

•MT63 1k/long interleave – relatively fast and best suited for detailed situation reports and formal messages under moderate to good HF conditions

•MT63 2k/long interleave – very fast and extremely effective on VHF/UHF FM

Accuracy, speed and audio bandwidth all come into play and various modes all have their advantages and disadvantages!

Audio Level SettingsTurn that thing down!

Distortion and non-linear operation (splatter) is caused by overdriving your sound card audio into your radio and it causes severe interference to other stations within theaudio passband of the receiving stations!

Good A bad neighbor

Overdrive also increases the error rate at the receiving station

Audio Level Adjustment

Set your radio RF output to it's maximum power levelAdjust your sound card mixer master volume to minimumSet your radio meter to ALC (automatic level control)Click the “Tune” button on fldigiIncrease your mixer volume control until the ALC meter begins to registerBack off until no ALCReduce the audio drive (or the transceiver power level) for the desired output levelYou will have just about a perfect transmit signal for ALL modes that fldigi produces

Audio Level Adjustment

Turn off the tune signal and try sendinga PSK-31 idle signal (no keyboard input)

You should see your power meter fluctuate.

As you send text the fluctuation will increase.

This is your goal: IMD = -30 dB

Sound Card Calibration

Sound card accuracy is most critical on MFSK, Olivia and MT63.

The errors between your sound card transmit and receive clock and an externalstandard is measured in parts per million (PPM) based on a given sample rate.

If there is a discrepancy between your Tx and the receiving ends Rx sample rate, the result is the person on the other end of the QSO may not properly decode your transmitted text

If there is a substantial difference between your Rx and Tx sample rates the otherstation may have to tune your signal after every exchange.

Two ways to calibrate:•By receiving WWV - best•By using a third party software which calibrates sound card to computer clock (OK if your computer clock is very accurate)

Sound Card CalibrationWWV method

Select the WWV operating mode and tune the radioto WWV at 5, 10 or 15 MHz.Use USB or AM mode on the radio

The waterfall looks like

Sound Card CalibrationWWV time tick

NBEMS

Preferred

Modes

DominoEX-11 MFSK-16

Olivia 16/500 MT63-1000

DominoEX11

DominoEX11 provides excellent keyboard to keyboard communications. It is excellent on HFwhen conditions are poor to good. This mode provides a reliable means of sending and receiving short messages. Tuning is not critical.

MFSK-16

MFSK16 is a multi-frequency shift keyed. It has low symbol rate and a single carrierof constant amplitude which is stepped between 16 tones. As a result, no unwanted sidebands are generated, and no special amplifier linearity requirements are necessary. This is one of the few modes that you can overdrive without fear of splatter.

This mode uses full-time Forward Error Correction, so it is very robust. Tuning must be very accurate, and the software will not tolerate differences between transmit and receive frequency. The mode was designed for long path HF DX, and due to its great sensitivity is one of the best for long distance QSOs and schedules.

Olivia 16/500

Olivia 16 tones, 500 Hz mode is good for formal short message handling. Although the mode is relatively slow (about writing speed), it is very accurate, even under extremely poor conditions.Accurate decoding can occur when the signal can be neither seen nor heard.

A large amount of forward error correction is utilized in this mode, making it suitable for mission critical messaging when used by properly trained operators.

Sound card calibration is critical, but once the proper calibration procedures are performed, the settings are saved and accuracy is retained without the need for further adjustments, unless the sound card is replaced.

See the QST article in the December 2008 issue for a very good explanation of just how well this mode performs under even the worst HF conditions.

MT63 1k, Long Interleave

MT63 1k long is ideal for portable, mobile and fixed station operations on HF and for use withVHF/UHF ssb. It provides good decoding under moderate to good s/n conditions. It can be useddetailed situation reports and database transmissions on VHF for the following reasons:

Very effective under moderate to good RF conditionsExtremely accurate decoding (major duplication of data and forward error corrected) Works extremely well under QRM and QRN conditions Can be used with audio coupling but direct interfacing is recommended for all digital HF operations

Tuning procedures and sound card calibration are critical with MT63 on HF, so the mode requires some training and practice. But once the use of the mode is mastered, it is extremely efficient. The speed at which MT63 1k long operates, makes it possible to send detailed reports that would not be practical using voice transmissions at writing speed.

This mode required a very linear transmit / receive transmission path.

MT63 2k, Long Interleave

MT63 2k long is an excellent choice for local portable, mobile and fixed station operations on FM channels (repeater or simplex). It is extremely well suited for detailed situation reports and database transmissions for the following reasons:

Can be used very effectively without a sound card interface (audio coupling) Extremely effective, even under very poor simplex RF conditions Extremely accurate decoding (major duplication of data and forward error corrected) Very forgiving on sound levels and requires no tuning when used on FM Excellent for sending larger situation reports or databases

MT63 2k long has been in use in Western Pennsylvania in several drills and public service events since 2005. The mode performs extremely well even under very adverse conditions. The fact that all one needs is a hand held transceiver and a computer (no need for sound card interface or any other hardware) makes the widespread adoption of this mode, for use on FM simplex and repeaters, a very attainable goal.

This mode requires a very linear transmit / receive transmission path.

Mode Comparison

Mode Speed Duty Cycle Bandwidth Linear Path

DominoEX-11 80 wpm 100 % 262 Hz NO (1)

MFSK-16 58 wpm 100 % 316 Hz NO (1)

Olivia 16/500 19.5 wpm 100 % 500 Hz Yes (2)

MT63-1000 100 wpm 80 % 1000 Hz Yes (3)

MT63-2000 200 WPM 80 % 2000 Hz Yes (3)

(1) a non-linear amplifier can be used for these modes(2) required to maintain corrected phase transitions between tones(3) required to maintain correct amplitude/phase in signal MT63 is essentially 64 simultaneous PSK signals spread across the bandwidth of the signal.

Automated Repeat Request

Flarq

Ancillary program acts as a client to the modem programTransfers blocks of data with checksumsBlocks are automatically repeated if not confirmedSending and receiving stations are locked in a handshaking mode during the entire transfer.Does NOT compensate for s/n – ARQ requires a good to excellent signal path.It does provide absolute confirmation of receipt.Cannot be used for broadcast type transmissions.Requires either fldigi or MultiPsk for the modem transport layer

Wrap

File encapsulation for broadcast transmissions.A single application both wraps and unwraps transmitted filesAllows for unattended reception of broadcastIdeal for transferring columnar data such as a spreadsheetEnables the transfer of plain text, image and binary filesVerification of accuracy occurs at each receiving stationVery simple to use – drag and drop files for wrap / unwrapCan be used with any digital modem program program must not alter the ASCII characters

Fldigi can automatically capture and save “wrapped” files asthey are received.

Here are some useful links to sites with more information on NBEMS:

Official NBEMS Site:http://www.w1hkj.com

WPA NBEMS Site:http://www.pa-sitrep.com/NBEMS

CheckSR Sound Card Calibration Application:http://www.pa-sitrep.com/checksr/CheckSR.exe

Fldigi on-line help:http://www.w1hkj/FldigiHelp

Fldigi on-line mode identification – sight and soundhttp://www.w1hkj.com/FldigiHelp/Modes

NBEMS official email list:http://groups.yahoo.com/group/NBEMSham/