View source for FLDIGI: What it is NOT What it can do for ARES RACES

 Date: Sun, 6 Mar 2011 09:52:42 -0500
 From: Andy obrien <k3ukandy@gmail.com>
 Subject: [digitalradio] Some thoughts on Fldigi... what it is NOT... what it can do for ARES/RACES

This is NOT a comprehensive guide, if you wants details see any of the
links below

 http://www.w1hkj.com/beginners.html
 http://www.pa-sitrep.com/NBEMS/fldigi_start.htm
 http://www.midcoastdigiham.belljar.net/vhf_digital_quickstart.pdf

This brief article is intended to explain Fldigi and its use in
emergency communication , mainly for those who have no clue what it
is,  or what is done with it.

Within the past few months, the use of Fldigi by radio amateurs
involved in emergency communications has risen sharply.  The average
ham that uses HF digital modes is probably quite familiar with Fldigi
, as its has been developed over the past few years and joined
Multipsk, Winwarbler,  DM780 , and MixW  as a common application for
digital operations.  Listening to comments from some emcomm hams, it
appears some  have  misconceptions about what fldigi is.  Within the
past few weeks, I have heard some describe Fldigi as a new "mode", I
also heard some recently described Flmsg as a "mode".  Today , I also
heard someone on the air say that they needed to start a Fldigi node
in their county. I have also heard a few references to NBEMS as a
"mode".  So, I thought I would write a few words for those who have no
clue,  make it a little easier to understand.

Fldigi is a multimode digital application, that has versions that work
under Windows and Linux.  In many respect, Fldigi is no different from
Multipsk, Mixw, and DM780.  It is an application that allows the ham
to have QSOs using common digital modes like PSK31 and RTTY.  It also
has an extensive list of other , less common, digital modes like
Olivia, Feld-Hell, MT63, THOR, Domino, MFSK16 and many more.  The
majority of Fldigi users us it for plain digital mode rag-chews and
DXing.  Within the past 3-4 years, Fldigi has gradually added some
extra features that have excited the radio amateurs that provides
emergency communications.  Note , these are "extra" features, not
really extra digital modes.  The extra features started with a few new
concepts in Fldigi. a concept called NBEMS (Narrow Band Emergency
Messaging System (See http://www/arrl.org/nbems).   NBEMS essentially
added some point-to-point email and file transfer capability to
existing digital modes.  A special type of error correcting process
was added using ARQ concepts, thus the ham could use common modes like
PSK31, or MFSK16 in ARQ mode to send email, or text files.  Like other
ARQ modes, this involved sending the message and having the other
station confirm reception of blocks of the text .  So, this station
and may others around the world had the capability to establish a QSOs
and send text error free, no new modes involved, just using what we
normally use for everyday digital chats.  No "nodes" are used, in fact
those behind the project were opposed to the concepts of nodes that
transmit frequently while unattended, The NBEMS FLARQ methods just
needed a a regular QSO to pass "traffic".

As many hams began to experiment with FLdigi for emcomm operations ,
the Fldigi software began to add features based on the input of hams,
especially groups in South Carolina and Western Pennsylvania,  who
held extensive experimental nets both on HF and VHF/UHF.  In the past
year or so, FLdigi added the capability to format text in a manner
useful to , MARS, RACES and ARES members.  The significant development
was the addition of an adjunct called FLMSG.  This seamlessly
integrates with Fldigi and enables the hams to format text in a
variety of ways common to emcomm, specifically NTS message templates,
and many FEMA/NIMS message formats.  So, the ham that is serving an
agency like FEMA, Red Cross, or Salvation Army , can transmit messages
in their original format.  No having to transmit a raw ASCII file that
looks unfamiliar to the served agency, it can be viewed in its
original format.

So, Fldigi employs regularly used digital modes to transmit messages
created in FLMSG .  No special modes, on the contrary..  almost any
digital mode in common use can be used.   Some modes are better  than
others under varying conditions.  Some modes are very fast , some are
very slow.  The slow modes may not be very effective if large text
files  are being transmitted.  ARQ modes in particular seem to slow
down a lot due to all the "acks" and repeats requests.   The fast
modes are sometimes not very accurate if a band is noisy or in poor
shape. ,   In non-ARQ modes ,  message like "Watson, come here" , may
get decoded at the other end as "Hatsxn, come herm" or perhaps "Matson
come here".  So, based on input from users, and clever programming by
the Fldigi development team, they added  a method of devising a
check-sum for messages being transmitted.  If the receiving station
compared the check-sum, they would know that the received message
contained errors and could as for a repeat .  This allowed the sending
of a complete message without getting bogged down with ARQ-type
repeats and acks.  This method involved the use of the WRAP file
system and was Incorporated in to another FLdigi add-on... Flwrap.

Just to get everything clear,  the above means that the multimode
application , Fldigi, still did its usually digital mode rag-chew
applications... but it also has the ability  to send messages via
modes like PSK31, PSK250, MFSK16 , MFSK32, in ARQ mode, or files in
"regular" mode,  with a check-sum , using any of the aforementioned
modes, plus others like MT63.  So if I wanted to send a emergency
message  and had Fldigi at my disposal, I take the same software I use
everyday, use the same modes I use everyday,   but I can add a few
extra twists for accuracy, ARQ or WRAP messages.    I do not look for
known "nodes" or "server" stations.  In emcomm work I will usually use
pre-arranged sections of the HF band, or known repeaters.

The Western PA and South Carolina hams experimented with both HF and
VHF/UHF use of digital modes.  They knew that digital modes work well
on a noisy HF band.  They also determined that,  just like packet
radio on VHF/UHF, the relatively noise free VHF/UHF bands provided an
opportunity to use several digital modes at higher speed . Using wider
bandwidth.  just like the old packet days when 300 baud packet was
boosted to 1200 baud on VHF.   They also discovered that some modes ,
like Olivia and MT63,  did quite well when simply holding a hand
microphone to a speaker, thus in an emergency, some messages could be
sent without extra equipment like a sound card interface.

Other hams in Europe and elsewhere also developed an email system via
HF radio, PSKMAIL.  This allows a ham to make contact with a "server"
on a given frequency, and delivery mail for i insertion in to the
Internet.  PSKMAIL support has also been added to FLdigi.

So, how does  all this work for the ARES/RACES ?  The many uses of
Fldigi work best if the average ARES/RACES member uses digital modes
on a regular basis, using the modes for "fun", rag chews, and
information exchange via local nets or simple QSOs. In the average
RACES or ARES "drill" it is likely used to supplement  voice
communications, not replace them.  Digital modes are likely used when
an ARES/RACES station  has already established voice  communication
with a desired target station  (e.g. an EOC or shelter) , during the
event an agency may request that RACES/ARES send information that is
very detailed , and accuracy is very important.  Via voice, to ensure
accuracy, NTS-style radiograms could be used effectively . but the
dictation speed needed for accuracy will slow things down quite a bit.
 If voice is the only means available, it will still work well, but
the ability to use error correcting or error checking digital modes
will greatly assist the operations.    So, in a real situation,  the
ham station may be having brief voice communication with an EOC or
shelter and then decide to send a ICS-213 or Red Cross 5266 form via a
digital mode.  Fldigi gives you a very wide array of choices as to
which digital mode will be used.  The most common used are Olivia,
MT63, or PSK.  You would decide based on what conditions you are faced
with and what mode you are "comfortable" with.  If you use  these
modes as a regular part of your amateur radio operations, you will
become quite familiar with the advantages and disadvantages of each
mode.  Olivia 500/8 is slow but very effective on HF when conditions
are very poor, MT63 1000 (long interleave) is quite fast and also
works well on a noisy HF band. MARS stations use MT63 a lot.  MT63
2000 and PSK 250 or PSK500 work very well at high speeds on VHF or
UHF.  So the correct language for the emcomm ham to use is ... not
that they are using "Fldigi mode" ... they are using MT63 mode or PSK
mode, or Olivia mode.  They are using the  Fldigi software to transmit
and receive communication via several modes.  Anyway, lets get to the
situation where that served agency asks the hams to send an ICS-213 or
Red Cross 5266 (or any other information in text format) .  In this
era of laptops or desktop computers, it is likely that the served
agency has this information on their computer.  They can simply give
that file to you via a thumb drive, ir some other file transfer method
from computer to computer.  You, the ham extraordinaire, can bring up
Fldigi on you computer, import the Red Cross form or ICS form , choose
which digital mode you and the other station(s) are using and transmit
the form.  You will have also decided whether you are sending as a
check-sum encoded "Wrap file" or using NBEMS recommended modes that
use ARQ methods.  The thinking nowadays is that the Wrap file method
is quicker even if a re-send or two is required due to a bad checksum.
 By the way, if the served agency does not have an ability to give you
the information from an already typed document, Fldigi with FLMSG
allows you to type it yourself and then transmit it, all in the
correct form format.

The actual transmission of information via digital modes involves a
little equipment.  At its most bare bones, you need a computer that
will run the software (Windows or Linux), that computer should have a
soundcard.  You then can hold the microphone to a speaker, key the
rig's microphone while transmitting your text , and press the TX
button in Fldigi which will create the tones and send the information.
 I was very skeptical of this method since being an old HF digital
operator, I was familiar with the usual method of feeding both
transmit and receive audio via direct audio cables from computer to
the rig.  On HF this "acoustic coupling", holding the mic to the
speakers, does not work well for weak or even moderate signals.  On FM
VHF of UHF repeaters it works surprisingly well.  Still, it will
"better" if you connect your rig and computer directly.  Some modern
radios have PSK31 and RTTY already build in, no computer or sound card
is needed.  However, most emcomm users will be using a radio that does
not have built in digital modes.  To receive digital modes, all you
need is an audio cable that takes the sound OUT from your radio to an
audio input on your computer (usually Line in or Mic In) .  Using a
simple audio cable and software like Fldigi, you will then be able to
decode the signals being received. However, when it comes to
transmitting these modes via a direct connection between rig and
computer, there are a few things you need to know.  If you already
have something like PSK31 in you station, you already know this, all
aspects of Fldigi should work well with your existing set-up.  If you
have never tried digital modes,  for transmission you will need to
connect the audio tones generated by your computer/soundcard to the
rig for transmission over the air.  The connection is usually made
from the Line OUT of the computer to a "transmit audio" pin on either
an accessory jack, or mic connector on your rig.  Directly connecting
the computer and rig can introduce "hum" via ground loops and
introduce RF in to your signal.  This distorts your transmission and
your signal is too distorted to be copied at the other end,  So most
hams use a circuit that "interfaces" both the received audio and
transmit audio from rig to PC.  The circuits facilitate control of
your rig's TX/Receive PTT commands, and also include isolation
transformers that reduce or eliminate ground loops thus keeping your
transmitted signal "clean".  You can easily build an interface for
less than $30.00, see http://sites.google.com/site/kh6tyinterface/
or you can buy one of many commercial interfaces.  Some of the
commercial interfaces include built-in sound cards, some do not.  Some
use VOX circuits and some have a choice of many methods to interface
with your rig.  They range from $50.00 to 500.00 .  I use a Microkeyer
by Microham. Many use products by Signalink, Rigblaster, Donner,
Tigetronics Navigator, and lots more.  Google these products and read
reviews that will enable you to make a choice.

Any questions, feel free to ask.  Also consider using the following
Yahoogroups and ask more questions

 http://groups.yahoo.com/group/digitalradio/
 http://groups.yahoo.com/group/panbems
 http://groups.yahoo.com/group/win-fldigi/
 http://groups.yahoo.com/group/NBEMSham/
 http://groups.yahoo.com/group/panbems/

You can also see youtube videos of Fldigi

 http://www.youtube.com/watch?v=SWZ2vKWSilE  (Setting up MT63 for FM use)
 http://www.youtube.com/watch?v=-r_62rX1GPM  (RSID with NBMES / FLDIGI - Advanced Settings for Unmanned Monitoring Stations )
 http://www.youtube.com/watch?v=lG6_-wIi1E0  NBEMS FLDIGI WRAP Checksum Demo
 http://www.youtube.com/watch?v=gfYXneVlrCo  demo of MT63 on a repeater with Tigertronics interface
 http://www.youtube.com/watch?v=4J-e7u4wxmc  Fldigi with ICS-213 form
 http://www.youtube.com/watch?v=PWCufvaEwS4   PSKMAIL

 Andy K3UK


==Referensi==

* http://www.obriensweb.com/fldigiemcomm.html

==Pranala Menarik==

* [[Komunikasi Digital Amatir]]
* [[Amatir Radio]]