CW Radiotelegraphy – A Robust mode

CW Radiotelegraphy – A disaster surviveable mode CW Radiotelegraphy is the oldest mode of radio communication and yet perhaps the most robust mode available to mankind to date. CW Radiotelegraphy is an adaptation of the cable telegraphy based on the Morse code signalling method for text communication devised by Samuel Morse way back in the year 1837. After some refinements, Morse code could be used to communicate through uppercase alphabets, numerals, and several punctuation marks. The structure of the code has been intelligently designed to provide high efficiency by assigning shorter code sequences to the alphabets that were more frequently used in the formation of English language words and sentences. Marconi used the Morse code to conduct the historic maiden radio contact. The transmission of Morse code over the radio waves thereafter became the standard method of radio communication. All other modulation modes like radiotelephony etc came into existence much later. With the advancement in technology, many different modes of information modulation over the radio were developed over the centuries. However, Morse code transmission over the radio, despite its early... Click Here to Read Full Article […]

Data & Text Mode digital Radio

Data & Text mode Digital Radio Communication Data and Text mode digital radio communication has matured over the decades and now forms an important aspect not only of professional and commercial radio but is also an integral part of amateur radio. Radio amateurs have been in the forefront of the process of experimentation, development, and validation of workability and reliability of many of the digital communication modes that are in vogue today. The earliest text mode digital radio communication protocol that was used for effective long-distance radio communication of text messages was Radio-Teletype (RTTY). This was a straightforward and very basic mode that used binary FSK over a narrow baseband and was essentially an extension of cable teletype. However, even though there has been rapid evolution that brought in scores of new, more reliable, efficient, and robust protocols, RTTY still remains firmly entrenched to date. Whereas, with the advent of advanced technologies and computer algorithms and with the passage of time, several digital modes that came into being at one time often fell by the side only to be replaced... Click Here to Read Full Article […]

Radio Signal Modulation Principles

Introduction to Radio Signal Modulation For serving the purpose as a practical communication medium, the radio wave has to undergo a process of radio signal modulation. There are several ways of achieving the objective. For instance, we are all familiar with medium-wave and shortwave AM radio broadcast, or the FM radio that not only sounds better than typical AM broadcast radio but is also capable of stereophonic transmission. Then again, we have television broadcast transmissions that allow us to see motion pictures along with the synchronized sound. Other than these, messages are transmitted from one place to another for commercial use, military, maritime-mobile, aviation, space communication, telemetry, etc. The applications of radio communication are endless. We as radio amateurs have had the radio as a medium for almost a century in various forms and experimented with various aspects. We are all perhaps familiar with some of the fundamental aspects of the process of radio signal modulation. For instance, we are conversant with the terms Amplitude modulation (AM), Frequency modulation (FM), single-sideband modulation (SSB), etc. With the dawn of the digital... Click Here to Read Full Article […]

Amateur Satellite Communications

Amateur Satellite Communications – An Introduction Amateur radio satellite communications present unique opportunities as well as challenges that are different from what we experience with terrestrial HF, or VHF/UHF. Let us examine the important aspects and get started. Although commercial and military satellite communications and other space applications involve several intricate technologies, we will focus on satellite communications systems related to amateur radio use. We have already touched upon some important aspects in our articles related to Space Radio Propagation and Earth Satellite Orbits. You are welcome to peruse these articles to familiarize yourself with some of these important aspects to get a holistic view of the underlying principles. Amateur space satellite communications began way back in the 1960s with AMSAT OSCAR series. The initial satellites only used analog linear transponders and telemetry beacons in Low Earth Orbits (LEO) that were nearly circular. However, with the passage of time, amateur radio satellites have expanded in variety by including digital modes, FM repeaters, DATV, etc. Although by and large most of the amateur satellites are still placed in LEO we also... Click Here to Read Full Article […]

Radio Communication Microphones

Radio Communication Microphones – The Untold Story How to optimally set up and use a microphone in a radio communication environment? This is perhaps one of those questions that rarely tickle in the minds of radio amateurs. Their minds are usually preoccupied with, what they believe to be more pressing matters like selecting a latest-model of a jazzy transceiver, or a fancy accessory, etc… So, many people don’t even bother to think twice about a small thing like a microphone. Although the microphone might appear to be trivial, it actually, goes a long way in shaping the overall on-air performance and quality of the radio station. In this article, I will walk you through some of the important factors related not only to the selection of a microphone but also to its optimal placement in a ham-shack environment. Fortunately, most commercial manufacturers of radio transceivers include a suitable microphone as a standard accessory. Typically, these are handheld microphones with a PTT switch. While transmitting, a radio operator would hold the microphone close to his mouth and press the PTT to... Click Here to Read Full Article […]

EME Moonbounce communication

EME Moonbounce Communication – Getting Started Earth-Moon-Earth EME Moonbounce communication is a very fascinating aspect of amateur radio. This is the earliest application of earth satellite communication ever attempted by radio amateurs. Well before the first artificial earth-orbiting satellite was placed around our planet, the moon was used to bounce radio signals off its surface for establishing communication between radio stations on earth. Unlike the man-made artificial satellites that orbit the earth at relatively lower altitudes, the moon is a natural earth satellite that has the highest known altitude. Moreover, the man-made satellites are active and carry transponders and repeaters while the moon can only perform as a passive reflector thus adding far greater challenges. Successful attempts at bouncing radio signals off the lunar surface were done in 1953, however, the first successful two-way communication was established in the early 1960s. Ever since then, radio amateurs from around the world have been using the lunar surface to establish Earth-Moon-Earth (EME) Moonbounce communication. The earlier contacts were made using slow-speed CW and large antenna arrays were driven by transmitter output of... Click Here to Read Full Article […]

Digital Modulation Fundamentals

The fundamentals of Digital modulation for radio The 21st century has seen a major upsurge of digital modulation methods in radio communication. It is, therefore, imperative for all amateur radio operators to attain a clear insight into some of the essential fundamentals of digital modulation techniques and also to how and why it is done. In this article, I will attempt to walk you through some of the basics and also take a look at the genesis and evolution of digital radio communication. The average radio amateurs who come from various academic backgrounds and may not have an electronic or electrical communication leaning often find it difficult to relate themselves to the stereotypical explanations of the various nuts and bolts of the digital communication model. The objective is to keep this narrative intuitive and simple without dwelling into the associated mathematics as much as possible. Other than the use of digital modulation methods to implement digital voice communication and file transfer of documents, images, etc, the most common digital modulation methods have been used very effectively to implement text mode... Click Here to Read Full Article […]

Slow Scan TV (SSTV) – How it works

Slow Scan TV (SSTV) – Analog and Digital Slow Scan Television or SSTV is essentially a derivative of the wideband broadcast television system that we are so familiar with. The fundamental principles of SSTV signal structure and modulation are fairly similar to that of the regular TV. However, the primary difference lies in the fact that while the regular commercial television displays motion pictures along with synchronized sound, the SSTV protocol only allows for still pictures to be transmitted over a radio channel. Secondly, picture frame size and resolution are far less for SSTV in comparison to regular TV. SSTV had been conceived around the year 1957-1959. It was inspired by the existing Facsimile system known as Radio-Fax. However, it was not practically suited for amateur radio use over HF radio primarily because of the long frame transmission time required for Radio-Fax which was around 20 minutes. Although the frame resolution of Radio-Fax was high, the long transmit time was rather impractical for amateur radio use. Amateur radio needed to derive a picture transmission protocol that even though might feature... Click Here to Read Full Article […]

Noise in Radio communication

Introduction to Radio Communication Noise As important as the desired signal, the aggregate undesired noise in radio communication is a factor that is equally important. The insight into the causes and sources of noise are vital to determine a radio communication link feasibility and to determine its capabilities, reliability, robustness, and immunity to failure. Noise in any communication environment may arise from several sources. Therefore, it is imperative to identify and understand each of these noise sources and also to understand their characteristics. After all, what is noise? Is it something characteristically different from the signal? Can the signal be extracted and isolated from the noise by any simple method?… To be able to answer these questions, we need to look deeper into the anatomy of noise. To begin with, the basic composition of radio frequency noise is no different from the radio signal. They are both electromagnetic waves and they both reside in the common passband that is occupied by the desired signal. So, how do we get rid of the noise? The short answer is that WE CAN’T…... Click Here to Read Full Article […]

Atmospheric impact on VHF Radio Propagation

Atmospheric influence on VHF Radio Propagation The overall influence and impact of atmospheric conditions on VHF radio propagation are quite significant. In this article whenever I mention VHF, it would usually refer to both VHF and UHF bands. Although the magnitudes of various effects due to atmospheric factors would vary, the pattern of behavior on both these bands would follow a similar trend. The upper part of the UHF spectrum beyond 1GHz leading into the microwave spectrum would of course exhibit distinctively different behavior. Therefore, we will maintain our focus on the atmospheric impact on the VHF and lower UHF band with an emphasis on the amateur radio bands of VHF (2m) and UHF (70cm)… Secondly, when I speak of VHF radio propagation, I would be referring to only terrestrial point-to-point communication and not the earth-space communication. The parameters governing earth-space communication are often quite different. Another important factor to keep in mind is that the atmosphere is a very wide region above the earth extending upwards up to 650-900 Km. Within the atmosphere, there are many sub-regions, of which,... Click Here to Read Full Article […]