Digital Radio Primer - Part 8
by AD5XJ Ken
These are my comments on digital communications and are not necessarily all there is to know on the subject. As with everything computer related – there are at least six ways to do the same thing. Given this caveat, let me say this is opinion and not the complete story. I only relate to you my experience of 5 or more years using digital modes and as SATERN International Digital Net Manager to give you the benefit of my experience. I will leave the rest for you to research as you see fit.
PACTOR vs. WinMOR vs. FLDIGI
From time to time the question comes up as to what should operators use to send messages. Sometimes the variant to that question is “Do we use WinLink or FLDIGI or something else?”. This is not a simple question to answer and there is no one perfect answer. It depends on the organization, the goal of the individual group and purpose of operation, and existing band conditions – in other words a lot of variables are involved, and the solution to that decision is also variable. To help with possible answers, lets look at the primary purpose of each of these choices.
As we learned in Digital Communication 3 - “Winlink 2000 (WL2K) is a worldwide system of volunteer resources supporting e-mail by radio, with non-commercial links to Internet e-mail.”. What that boils down to is that WinLink 2000 can serve the purpose of Internet email when the normal access to the cloud (Internet Service Provider) is not available. Such was the case in the last several hurricanes in the Louisiana, Mississippi, and Texas ARRL Sections. When such devastation occurs, WinLink 2000 RMS stations are invaluable as backbone support to the Internet email system as well as an important message vehicle to emergency and first responder resources. It will quite naturally be heavily used in those occasions of emergency and wide spread loss of infrastructure.
WinLink 2000 has the flexibility to use more than one digital mode to connect to WinLink clients. Many emcomm organizations have defaulted to PACTOR by using SCS modems - hardware TNC implementations of PACTOR II, III, and IV. Recently, software based solutions like WinMOR and ARDOP have emerged that are inexpensive computer soundcard based and do not require external hardware implementation.
Either way, WinLink has a narrow focus on Internet style messages with or without attachments. The WinLink development team has recently added a non-formatted version of some of the FEMA/ICS message forms to the RMS Express client software. While this is a significant step forward in the usefulness of WinLink in the emcomm effort it nowhere nearly comes close to the FLMSG pre-formatted ICS forms in appearamce and style.
One of the disadvantages of WinLINK 2000 is that it is a Client / Server type system which uses clients stations connected syncronously (through FEC and ARQ radio connections) to transfer messages. This means that clients must be “connected” and the client-server connection is the only message path (no data is revealed in monitor mode). Additionally, WinMOR mode has a peer-to-peer sub-mode that allows other clients (peers) to connect one at a time to each other. The message path is then one to one (i.e. peer-to-peer).
Contrast this with the SATERN International Digital Net operations where we have the ability to transfer messages peer-to-peer, as well as NCS broadcast to volunteers as a group with the FLAMP broadcast facility employing a variety of possible modes. We have the flexibility of using which ever mode is most error-free at the moment of transmission. We also have the ability to send text, small pictures, and other files peer-to-peer in ARQ mode, as well as a general broadcast to all on frequency. The FLAMP sofware provides error-free movement of messages in asynchronous broadcast mode.
Does this mean that SATERN should not use WinLink 2000 to send messages? Not at all. In many situations we may be supporting other organizations like ARES, MARS, or any relief organization that may need to send email over WinLink. We have the ability to take simple peer-to-peer (p2p) messages from satellite stations with limited capabilities and transfer those messages (as is, or formatted) by WinLink where needed – given the caveat that attachments or large image files must be sent simultaneously and may take long transmission times depending on the current operating mode. The Internet email is then assembled and sent by the receiving station that has ISP service or by WinLink 2000.
Perhaps this is a confusing concept, but what it amounts to is a demonstration of the inherent, vast, flexibility and interoperability of our ham radio volunteer organization. When we embrace multiple media and methods, we are able to provide the maximum of utility and flexibility that so characterizes ham radio as a provider of emergency communication.
It is not helpful when those who continue to resist new technology propose that even the prospect of anything other than voice or CW is not “real” ham radio. SATERN will continue to use and embrace any media or method available to amateurs that will get the message through. The SATERN International Digital Net will continue to expand our capabilities as new technologies emerge.
The next mode to emerge for general use, will likely be ARDOP. This new mode, in development, may be used in both keyboard to keyboard (k2k) mode as well as synchronously in ARQ mode over WinLink. Initial tests are proving that this mode is both fast and quite robust. It will be an Open Source product so that it will propagate over multiple hardware and software platforms (i.e. Windows, Linux, and Mac).
When fully released, ARDOP will have source code available to all who know how to use it, and will likely be incorporated in many multi-mode applications like FLDIGI and is already being tested using BPQ (a time-proven mail transport) as a message forwarding application. For now, we will see first full application of this new mode in BPQ, RMS Trimode, and RMS Express to support WinLink 2000.
One additional note: There has been a marked move in recent times to use Automatic Link Establishment signaling on the digital modes. As we discussed earlier, this is an implementation of MIL-STD-188-141A,B,C and STANG-4538. It provides multi-frequency calling and signaling as well as some ability to pass simple text messages (e.g. APRS position). There may be much more attention to use of ALE in some net operations. It is an accepted method and practice in MARS using both software and hardware ALE implementation. ALE has the unique ability to call and signal a singular station or group of stations by way of digital encoding of a packet of information. It requires a wide (2k) bandwidth for signaling and sounding but seems to be quite robust when used in adaptive modes.
Today there is a worldwide HF network of ALE users who monitor pre-determined frequencies on multiple bands. The HFLink network (see their web site at www.hflink.org) monitors these frequencies and have ad-hoc net meetings on other frequencies. As we are structured now, SATERN has not adopted the use of ALE on a regular basis. That is not to say any local or regional SATERN net could not use it. The utility has yet to be established for normal SATERN support operations of the Salvation Army. However, ALE may very well be encountered when interfacing with, or in support of, MARS, Military auxiliary support units, and some government agencies that use hardware-based ALE in their radios.