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