The New Amateur Radio University Network AMUNET (Part 2)

Transcription

1 The New Amateur Radio University Network AMUNET (Part 2) MIROSLAV SKORIC Faculty of Technical Sciences University of Novi Sad Skoric, P. O. Box 52, Novi Sad SERBIA AND MONTENEGRO Abstract: - This paper discusses external radio modems specific data controllers needed to build AMUNETs amateur radio computer networks at educational institutions and elsewhere. The paper lists various options being available with different groups of those devices and explains opportunities the users will have when decide what type of modem hardware to provide for most possible communicating implementations. Key-Words: - amateur radio, AMUNET, communication, computer, modem, data controller, education 1 Introduction One of the frequently asked questions after the amateur radio presentations at technical conferences and similar events is how to choose the most proper hardware and software solutions - following a decision to build the computerized amateur radio system at home or work. As expected, most of the prospective amateur radio communicators are interested in accomplishing these volunteer technical projects at lowest price as possible in particular if they reside in developing countries and/or rural areas [1]. Depending on local financial inputs and according the plans on what the AMUNET the amateur radio university network, should be capable to offer to local school or academia there is a variety of inexpensive or more costly hardware solutions. They differ not only in marketing price but in technical features and possible further communicating opportunities and options a user may imagine. At the very beginning, it is important to consider the main roles of the new-born radio network(s) in the elementary school, a college, the academic facility, in an urban environment or like. If it is the only goal to establish an ordinary '2-way' communication link between local school's kids and persons of same age in a neighboring educational institution and such link to be established on rare and temporary occasions then we have a plenty of simple and cost-effective modems available. In opposite to that situation, if the plans are to build advanced systems with more complex abilities, e.g. which would run for days and nights without switching off, or maybe being capable to store and forward larger quantities of bulletins and private messages while their system administrators (called 'sysop'-s in the amateur radio jargon) are off-line then some more costly approaches should be considered. In this paper we are going to discuss modem devices we install between radio transmitters and computers, and specifically those types that connect to the computers externally. In the next installments, we plan to cover internal modems, radio stations, antennas and other accessories, as well as the amateur radio computer software. 2 Most Common Types It is usual to differentiate modem and data controller categories in relation to their computer connectors. 2.1 Serial/LPT modems This group of data controlling devices has been popular and widely used for almost two decades now, Fig. 1. It works very well via standard RS232 serial ports at IBM-compatible computers, while having its power supply from the same computer connectors. That means the modem does not require an external energy source. Sometimes serial and LPT modems are built within the standardized connector enclosure. The most of serial- and 'Centronix'-fitted radio modems are suitable for all those school teachers who may want to practice and demonstrate the exciting radio communications to the pupils, while performing it occasionally and within not much prolonged time windows. For

2 technical school classes of app minutes per session, it is completely satisfying to provide such inexpensive devices at EUR each being connected to older PC-compatible computers. Such a solution completely covers most of basic communicating needs in a school. After a technical session is over, simple switching off the computer and radio station ensures that the modem is also without its power supply. No additional human action is needed. In the same time, no further incoming communication attempts to the school s radio equipment can be made from the outside world. On the other side, that is the reason why serial and parallel modems are less used in cases where computers have to be switched off, say, during the night or similar but where is still the need for 24/7 -type of modem activities (e.g. a personal mailbox, an automated answering machine etc). Generally speaking, there is not much difference between serial and parallel models. Have in mind that LPT devices are somewhat more updated constructions and that means they are more likely to accept so called 'piggy-back', additional printed circuit boards (PCB's) that allow higher data rates. On the other side, some of the 'parallel' designs require external power supplies, so those modems can not be powered directly from the connected computers. For that purpose, an electricity connector can be seen on bottom right end of the PCB in Fig. 3. With respect to well known fact that many radio amateurs are devoted not only to establish exciting world-wide communications, but to get new skills from building various communicating devices - there are several models that users can buy in a kit, the package of electronic elements prepared for home-made soldering. Those solutions are primarily devoted for more experienced customers and/or school labs equipped with all tools and instruments needed. In the same time, these kits are some 20-30% cheaper than the factory-made products. Fig.1 Modem for serial RS232 ports If there is a lack of free serial ports - 'parallel' ("LPT") models should be used instead, Fig. 2. The picture describes an even advanced design being capable to use the 'Enhanced Parallel Ports' (EPP). Fig.3 Modem with an external power connection Fig.2 Modem for a parallel EPP port 2.2 USB and TNC controllers Modern trends in computer motherboard designs try to abandon older connector standards of type RS232 and Centronics and their complete removal may happen in a couple of years. Following new technologies, manufacturers of the amateur radio devices have already offered new products equipped with USB connectivity. In parallel with that trend, it also appears that USB-fitted modems have more new features than the simpler devices, some of which described earlier. Actually, the new constructions can not fit within small 'COM' or 'LPT' connectors anymore, so they require larger and heavier enclosures. On the other side, they are often equipped with LED indicators, helping a user to

3 understand the unit s operating status and change its parameters with using micro switches on front and/or rear panels. Some of the new capabilities offered with the USB devices lead us to a conclusion that those new boxes have some similarities to another well known type of external modems: 'Terminal Node Controllers', or TNC's, Fig. 4. What differentiates simpler modems described at the beginning and TNC's is that the latter are almost completely autonomous devices. That means they can operate some of their functions even without computers switched on. You have plenty of TNC's to choose from these days. The amount of money you'll spend depends directly on what you want to accomplish. If you're only interested in packet operating, a basic TNC is all you need, says Steve Ford, [5]. In his book, there is not much comparison between 'classic' TNC devices - being produced since late eighties, and the simpler constructions we discussed earlier. Possibly Steve and other co-authors wanted their readers and prospective digital amateurs to settle with modems capable to answer all packet communicators' basic requirements. Most of the TNC's has equipped with microprocessors that manage their operations, as well as various RAM and ROM modules for data and instruction storage. With such complex designs, they are capable to do a lot more including sending outgoing and receiving incoming radio messages when the operator is not present or if the computer is out of power. Fig.4 Terminal Node Controller - TNC In addition, most of the TNC's are fully capable to run as 'node controllers' and that means such a device can be programmed with network node software (instead of the end-user communication program). In that case, the same or similar type and brand of modem can be temporarily or permanently placed on top of a high building or on a suitable position on the nearest mountain location. An example is repeater system "R" in Fig. 5. That way the radio amateurs can be interconnected in cases where natural or artificial obstacles shorten the radio paths, [2]. Fig.5 TNC as a part of a radio relay station Having such kind of an installation, almost any TNC behaves as a dedicated data 'traffic light' and allows the "packet-radio" amateurs - computer owners, living in the local area, to establish long distance links. In fact, a TNC-equipped network node behaves as a radio relay station and it helps making the long distances 'shorter'. Theoretically with a 'chain' of radio repeaters it is possible to establish a complex world-wide computer network consisting of many independent keyboard-tokeyboard connections without any commercial ISP or telephone service provider! The distances may be measured in thousands of kilometers - regardless the users running their small radios with few watts of output power. Having in mind that power blackouts are often expected in rural and remote areas, what could end in a loss of important data - the majority of TNC's are equipped with internal batteries that keep RAM and ROM content safe. That is also a useful option for home users who usually switch their computers off while in school or work. The energy from batteries is sufficient for recording incoming content. Besides that, the LED indicators on the TNC s front panel warn the user of a new mail, when returning back home. All the user needs to do is to power the computer, activate the communicating software and 'download' an incoming message from the modem to the computer desktop. 2.3 Multi-port devices A user who has only a single radio station will have no problems with the modems discussed before. The

4 question is what the users running two or more radio transceivers can do. The answer is to get one of the data controllers being equipped with two or more radio connectors. Sometimes such products are not much expensive than the single-port modems in cases the both outlets operate only one communicating mode (e.g. the VHF/UHF packetradio ). Multi-port devices have various opportunities: They allow the operator to simultaneously run two 'copies' of the same communicating mode. That means you can split your computer screen into two portions and establish two independent conversations while using two independent radio stations (i.e. frequencies, radio bands etc), Fig. 6. Besides that, very often there is a 'gateway' installed within such item and that even allows the incoming users to reach your station using one radio frequency and with the modem s gateway to switch to another frequency or the portion of radio spectrum. Just imagine a situation where your remote fellow amateurs use their own radios running at local 2m bands to approach the gateway of yours and from that particular point, they can switch to the gateway's 70 cm or some HF (high frequency) bands. Your friends would be grateful for having such an option! That feature can be not only interesting for remote radio correspondents but for the modem owners as well, provided they want to offer more services to their communicating partners. Fig.6 Two-port TNC 2.4 Multi-mode devices Besides the packet-radio as one of the simplest, most popular and widely implemented VHF/UHF and HF computer-related communicating modes, some modern data controllers offer even more capabilities and types of emissions (like Amtor, Pactor etc), Fig. 7. In case of the gateway within the box, you can allow your friends - coming from the Packet port(s) - to switch to your Pactor radio channel - as if they run their own local Pactor systems. Besides that, some of the combined Packet-Pactor products are useful for those individuals and groups of amateurs who plan to run the complex bulletin board system (BBS). Experience says that packet radio is completely useful solution and brings quite enough quality of data traffic at VHF and UHF frequencies, while on the HF bands bellow 30 MHz, Pactor performs significantly better. Eventually, Pactor got improved and today it is offered in more than one implementation: Pactor I, Pactor II etc. Fig.7 Three-port, two-mode TNC Before a final decision on buying a packet-only modem controller, or a multi-mode device equipped with a lot of bells and whistles, is about to be made, one should know that many features incorporated in multi-mode devices are suitable only on the HF bands so they have limited use on frequencies above 30 MHz. If your amateur radio license restricts you to work the VHF/UHF spectrum only, the higher cost of a multi-mode controller might not be worth the investment. That is why many beginners get the lower cost packet-only modems just to try new computerized communication and, in the same time, to determine if they like it. Later, they can dedicate the unit for local VHF connections with neighboring amateurs and purchase more complex modems to investigate the HF areas. This is a tried and true method, [3]. In my personal case, I have paid more attention to details like: If a unit will be capable to be reprogrammed sometime later in order to work with more than one type of communicating software and, in the same time, to be used not only as a simple keyboard-to-keyboard controller, but as an experimental software node and/or a personal mailbox when my computer is off. And as usual in the amateur radio research, after a couple of years and various experiments, I settled down to my primary role: to serve as a bulletin board system administrator. My packet-only terminal node controller works well on a local VHF channel most of the time. It did work on several HF

5 bands at 300 bit per second just to test its capabilities and it proved as fully functional. 2.5 Compare analog and digital systems Approximately years ago, the majority of amateur radio modems was made in analog technology. That meant, if a customer would not be satisfied with, say, a data speed that particular hardware offered - he/she had to buy an add-on electronic board that had to be installed within the box, Fig.8. Sometimes those new circuitries were not available on all world markets and even for all models of devices in particular after some couple of years of the first production. Discovering new approaches, like digital signal processing (DSP), it became possible to implement higher speeds and new communication modes with just uploading new TNC software ( firmware ) into data controllers. Some of those new luxurious and rather expensive devices are even equipped with LCD screens that help the operator to read the radio traffic even in the case the terminal, i.e. computer is off, Fig 9. Fig.8 Add-on board for 2400 bps Fig.9 Multimode DSP unit 3 Conclusions The examples given in this paper intend to suggest that plans for getting the proper equipment, prepared in advance, are needed before buying or building the initial amateur radio communication hardware. Here you have some more tips and reminders: The most of the digital radio amateurs have started their computer-related activities with ordinary 2-way links (a keyboard-tokeyboard chat ) with other enthusiasts within their amateur neighborhoods. If that can satisfy your needs, the simplest serial or parallel modems should be used. Though the simplest solutions may fit, the appetites tend to enlarge very soon. What differs to the home stations is an educational environment. Educators should consider possible further needs for some automated 24/7 facilities, BBS mailing systems, eventual satellite links etc. Then the appropriate decisions should be made. In cases where there are enough financial resources, often it is better to spend some more and reserve some advanced features that may be wanted soon after getting the initial communications skills and experience. Owners of two (or more) VHF radios operating on 2m and 70cm frequency bands may be interested in TNC's offering both 9600 and 1200 bps packet in the same package instead of two separate boxes. In case of a technical school or like, dedicated kits, i.e. packages of prepared electronic parts may be considered as even more low-cost solutions. The majority of simple serial and parallel modems discussed in this paper are constructed having on mind VHF-only data communicating needs, i.e. speeds varying from 1200 bps to 9600 bps. Should a user plans to broaden his/her activities so to include 300 bps on the HF (the areas bellow 30 MHz), a TNC having a possibility to switch from VHF/UHF to the HF operations, might be a better bet. According to [4], depending on the type of TNC you're using, you may have to send a command to place the unit in the HF packet mode. In opposite to such a software-related solution, the paper author's TNC has a micro switch positioned on the front panel that accomplishes the same task.

6 Regardless your next modem is going be a factory-made "plug'n'play" product, or a result of the school lab's experimenting output - the amateur radio in education should become strongly encouraged. Building own amateur radio equipment and accessories makes teachers and students not only consumers in today's world of modern electronics, but supporters of new ideas and innovations. Should you, as a scholar or student, consider implementing the amateur radio technology in your education environment, you do not have to be a computer expert! If you can read manuals and follow instructions, you can easily become an active 'packeteer'. Like any other facet of Amateur Radio, you're going to have to learn some new concepts, but that's part of the enjoyment, concludes Steve, WB8IMY [5]. References: [1] M. Skoric, The amateur radio as a learning technology in developing countries, IEEE ICALT-TEDC 2004, Proceedings, pp , [2] M. Skoric, The new amateur radio university network AMUNET, 9 th WSEAS Int. Conf. on Computers, Proceedings, [3] G. Jones, Packet Radio: What? Why? How?, TAPR, [4] S. Ford. Your HF Digital Companion. ARRL, [5] S. Ford. Your Packet Companion. ARRL, 1995.