Because HF communications are capable of covering such large distances and because they are so complex, you must plan out your system and your operating techniques in advance. Of course, in order to participate in two-way communications in the HF bands, you must have a receiver, a transmitter (these two may combine in the form of a transceiver), and an antenna. The type of antenna that you choose, the manner in which you construct it, and the ground system that it connects with are all key factors in the success of your operations.
HF transceivers vary greatly in type, power, construction, frequency ranges, operating modes, and other features, so you must be sure that you purchase a model that best suits your requirements. SGC makes a 20W SG-2020 and a 150W SG-2000.
Depending on your location, transceiver requirements will vary:
1. With the frequencies that you are allocated to use.
2. With the distance from your contacts.
3. With the amount of power output that you will require(only use as much power as necessary to make the contact).
If you use more power, many more people will listen to your transmissions and (especially for amateur radio operators) your signal could cause interference in the over-crowded amateur bands. As a result, some transceivers, including some of those from SGC, allow you to continuously decrease the power output.
In order to effectively communicate on the HF bands, you will probably need to spend some time "studying" the propagational effects first hand. The best way to do this is to purchase or borrow an inexpensive general-coverage shortwave receiver or a transceiver, if you don't already own one. Install an antenna and listen across the shortwave bands. The shortwave broadcast stations are fun and interesting to listen to, but most use tremendous transmitter powers--often as great as 500,000 watts output. As a result, you cannot really assess the range of your signal (or someone else's) just by listening to these broadcasters.
The best indications of the bands, the distance of skip, and the distances that you can cover are by listening to stations in the bands (the general frequency areas) that you will be working or by listening to nearby amateur radio bands. Some beacon stations operate in the amateur radio bands to provide radio enthusiasts with a guide to propagation conditions. Beacon stations usually transmit their call sign over and over in Morse code, according to a particular schedule (often 24 hours per day). If you listen to these beacons, know the power and locations, you can use them as an accurate yardstick to measure the conditions. If you are an amateur radio operator, you can check into several networks and ask those involved for an outlook on the present and upcoming propagation conditions.
Listening is one the most important aspects of having successful operations. It might not make a difference if you are using a 30-watt transceiver to communicate with someone a few miles away, but long-distance communications require radio experience and good-listening skills. Because of the static, fading, and interference that sometimes plague the HF frequencies over long distances, you must be able to mentally "filter out" this noise. Experienced "ears" can hear relatively low-powered AM broadcast outlets whereas the untrained listener wouldn't hear the broadcaster at all. To them, it will sound like static.
Over the HF spectrum, a number of different operating modes are used for two-way communications. The operating mode is format of the data and the manner in which it is transmitted. For example, although SSB and AM (covered earlier) are both in the voice format, they are transmitted in different manners. The following modes are used frequently across the HF spectrum.
CW (Continuous Wave) CW is a binary code that consists of "dits" and "dahs" as a transmitter is being keyed on and off. Although a number of different codes have been used since the days of the telegraph, only Morse code is widely used today. All amateur radio operators who use the HF bands are required to send and receive Morse code at at least five words per minute (wpm). CW might appear to be outmoded now that today's computers can reliably send and receive many types of digital communications. However, the CW signal is efficient because only the pattern of the signal (not the audio on the signal) needs to be understood and because the signal can be very narrow. As a result, CW is the most reliable form of communications for human operators.
AM (Amplitude Modulation) The AM mode consists of a base carrier, a modulated upper sideband, and a modulated lower sideband. See "Who Uses Long Range Radio Equipment?" However, some of the newer transceivers that have this mode use the SSB signal with a carrier inserted to produce a faux AM signal. Although true AM is the favorite mode of AM band and shortwave broadcasters, it is rarely used elsewhere because it is inefficient and because it requires a large amount of space in the already-crowded amateur bands. For the most part, the only AM two-way stations currently one the air are nostalgic amateurs who love the broadcast-quality audio from this mode.
SSB (Single Sideband)
SSB is one half of the voice component of the standard AM signal. The SSB mode, nearly always used for two-way communications across the HF spectrum, is so popular because the mode is much more efficient than any other voice mode and because the signals are narrower, so it is rarely hampered by fading.
RTTY (Radio Teletype) RTTY (often pronounced as "ritty") is one of the earliest forms of data communications. In this system, printed data is transmitted on a high-speed machine, rather than hand-keyed, as is the case with CW communications. Although CW is a form of data communications, it is copied by a human operator. Nobody can copy RTTY by ear. In order to send and receive RTTY, you must have other equipment in addition to the standard HF transceiver/antenna combination. Today, the most common arrangement would be to interface a personal computer with your transceiver and purchase the appropriate demodulating/modulating software or a computer interface. If no computer is available, then you would purchase a modulator/demodulator (MODEM), a monitor, and a printer.
The three major branches of RTTY communications are Baudot, AMTOR, and ASCII. The characters in Baudot code are formed by blocks of five-digit binary codes and an initial arrow--requiring something like a giant typewriter and printer combination in a desk-sized case full of gears. The catch with Baudot code is that it directly intermeshes with these mechanical printers and it is prone to interference--fades, static, and man-made interference, which cause errors in the received messages.
AMTOR is (simplified) RTTY Baudot code that has been modified to add various error-detection and correction enhancements. The AMTOR system corrects data by sending it in time-delayed chunks. The transceivers are connected to a "smart box"--a computer modulator/demodulator. Then, the transmitting station will send a block of data and the receiving station will receive it and transmit a signal back to verify that it received the signal. If the signals from the transmitting station are not received properly, then the receiving station will transmit a signal for the other station to repeat that block of text. This process will continue until the entire message is sent. Technically, this transmit/receive/verify process is called handshaking.
SITOR, a version of AMTOR, is used especially for marine and weather information. As a result, SITOR is mostly important for marine operators. Some Coast Guard and Marine Coast stations operate in the commercial marine bands. Otherwise, some frequencies in the 8- and 12 MHz bands are still audible. Just below the AM broadcast band on 518 kHz is a good bet for hearing U.S. Coast Guard information, which is broadcast to ships at sea.
ASCII is a term familiar to many people in the 1990's because nearly every computer editing system uses ASCII or some drivative of ASCII. As a result, it makes sense that ASCII would also be used to communicate data on the HF bands. Like Morse code and Baudot code,ASCII is a binary code. However, it differs from Morse because it uses 0's and 1's in the code (instead of dots and dashes) and it differs from Baudot code because it uses a seven-digit instead of a five-digit code.
BAUD: In digital transmission, whether RTTY radio transmissions or computer/modem transmissions, the speed by which the information is transferred is called the baud rate. It is determined by the bits of information (eash electical impulse) that flow through the system. Typical baud rates for computers are 300, 1200, 2400, 9600, 14,400 and 28,800 bps (bits per second). By the mid 1990's, most transmissions took place in the last three speeds. The baud rates for RTTY--mostly 100 bps or less-- are generally much slower because of the lower quality for the transmissions (static crashes, fades, adjacent-channel interference).
Packet Radio is one of the moste inteesting forms of data communications. It is so named because information is broken up into small packets and sent through the radio waves. Unlike the typical forms of data communications (where the send and receive process is noticeable), packet radio is more like having a wireless computer BBS. The packet messages can be stored and recalled at a later date, the communications are relatively error-free, and the information can be sent to many interconnected stations. The data transmissions are interesting and useful because they can be used essentially like E-Mail. RTTY doesn't have the advantages that it once had, now that the Internet has become "the information highway." Still, RTTY and packet radio are free to use if you are licensed to do so.
VIDEO: The most common form of video transmission is television. In addition to the broadcasts in the typical television band, special slow-scan television (SSTV) is also broadcast in the amateur radio bands. SSTV is different from regular commercial--Fast-Scan-- TV. SSTV differs from FSTV because the scan rate is much slower. That means that the screen is updated at a much slower pace than regular TV. As a result, SSTV is much more useful to transmit still images than moving images. Like the other forms of amateur radio, only noncommercial, two-way communications can be transmitted, so don't expect to watch your favorite show on the SSTV frequencies. In order to send and receive SSTV signals, you would need a TV or TV monitor, a scan converter, and camera, in addition to an HF SSB transceiver.
FAX: One amateur mode that is somewhat of a cross between a digital and a video mode is facsimile (fax). For most people, faxes were born in the 1980s; however, radio faxing goes back to the late 1920s when the mode was first experimental. Several years later, fax services, such as a special radio fax station that transmitted only the New York Times, were active. Like the standard telefax machines, radio fax sends the data line by line until the picture is complete. Some amateur radio companies are manufacturing relatively inexpensive modem units specifically to interface with computers and receivers so that you can send and receive faxes via the HF frequencies. For more information on data and video communications, check out the annual ARRL Handbook for Radio Amateurs by the staff of the American Radio Relay League, Your Gateway to Packet Radio by Stan Horzepa, The RTTY Listener by Fred Osterman, The Guide to World RTTY Stations and The Guide to Facsimile Stations by Joerg Kingenfuss, The Weather Satellite Handbook by Dr. Ralph Taggart, The Packet Radio Handbook (2nd Edition) by Jon Mayo, and The Amateur Television Workbook by M. Stone.
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