Terrestrial VHF Radio Signal Coverage – BLOS

Terrestrial VHF Radio Signal Propagation – BLOS This is part-2 of the two-part article series on Terrestrial VHF Radio Signal Coverage. This part will focus on Beyond-Line-of-Sight (BLOS) terrestrial VHF radio signal communication, whereas in part-1 we had discussed Line-of-Sight (LOS) communication. To recap what was discussed so far, check out the part-1 at Terrestrial VHF Radio Signal Coverage – LOS. When we refer to beyond-line-of-sight (BLOS) VHF radio communication, we include the non-line-of-sight (NLOS) circuit too. Strictly speaking, NLOS circuits are those which might have been regular LOS path had it not been for some natural or man-made obstacle that came in the way. As per spherical earth geometry, these NLOS paths would be within the radio horizon limits between the two stations. On the other hand, a BLOS communication circuit is essentially beyond the horizon or a trans-horizon circuit. The fundamental difference between the NLOS and BLOS circuit is that in the case of BLOS, it is beside the point whether there may or may not be obstacles in the path in the form of hills, mountains, buildings,... Click Here to Read Full Article […]

Miscellaneous Antennas

Classic miscellaneous antennas for communication Under our section on Miscellaneous Antennas, we will cover a variety of well-known antennas that do not typically fall under the genres like Yagi, Quad, LPDA, Wire Antennas, etc. These antennas are good and efficient antennas often used by radio amateurs as well as for various commercial and military applications. Some of these miscellaneous antennas are Cardioid pattern antennas, Four Square, Lazy-H, W8JK, ZL special, Moxon, Cobweb, Hex-beam, Bruce array, Bobtail curtain, etc to name a few. Many of them are multi-band antennas while others are mono-banders. Some of these antennas have quite unique characteristics with great performance. This is only an introductory article. However, under this section, we will from time to time expand upon them through in-depth articles and dwell into greater depths discussing their design principles, characteristics, and practical designs. Another antenna that is designed by yours truly, called the ‘VU2NSB OmniDX” antenna will also be presented. BTW, the list of antennas cited here is by no means exhaustive. These are only a selection of popular antennas in the miscellaneous category. Other... Click Here to Read Full Article […]

Understanding Antennas – The Good, the Bad, and the Ugly

Understanding Antennas – What makes them good or Bad? Are some antennas good while some others are bad? Many people seem to think so, but this notion is not entirely correct. Any such binary black or white classification is not the way to assess antennas. The fact of the matter is that all antennas that have been designed to radiate RF energy efficiently are usually good in their own rights. Yet I concede that the operator’s experience with a specific type of antenna may indeed be either good or bad. However, this does not necessarily mean that the fault lies with the antenna. More often than not it is the operator’s judgment in selecting the antenna or the way it is deployed that makes all the difference. Unless the antenna in question is technically a poor design that does not allow effective radiation to occur or the structural material used for fabricating the antenna leads to high loss resistance in comparison to its radiation resistance, there is no reason why the antenna will not be able to do the job... Click Here to Read Full Article […]

Geodesy for Terrestrial HF Radio

Geodesy and Maps for Terrestrial HF Radio Acquiring a working knowledge of the basic concepts of Maps and Geodesy for terrestrial HF radio communication is important to radio amateurs. The term Geodesy has its origin from the Greek language and is defined as a branch of applied mathematics concerned with the determination of the size and shape of the earth and the exact positions of points on its surface. This brings us to the concept of Geodesic Path in context to a spherical earth geometry. A Geodesic Path is the shortest path between two points on a curved surface, like that of the Earth. This is typically the path that is taken by propagating radio waves from one point to another. However, we must bear in mind that contrary to what some might believe, the earth is not strictly spherical in shape. The earth is slightly flattened at the top and bottom near the polar latitudes that give it a shape that appears to be a little bulged at the equator. This shape is termed as Oblate Spheroid or just... Click Here to Read Full Article […]

Elements of Amateur Radio Station

Amateur Radio Station (Ham Shack) A thoughtfully set up amateur radio station (Ham Shack) goes a long way to provide a pleasant and fulfilling experience for years at the end, in the world of amateur radio. Not only does a meticulously planned and well-configured station allow a person to enjoy the hobby to the fullest, but it also ensures adequate flexibility and scalability so that one may continue to upgrade his station without having to make drastic alterations to keep pace with the advancement in technology. This is notwithstanding the fact that a lot of amateur radio activity is also conducted using portable, field, or mobile equipment. A typical amateur radio station comprises two sets of hardware. They are a set of outdoor hardware comprising of the antenna and related stuff and a set of indoor hardware that comprises the transceivers and associated peripherals. The outdoor and the indoor hardware are interconnected through a transmission line that forms a very vital part of the overall radio station setup, however, unfortunately, it is often taken for granted and treated as trivial.... Click Here to Read Full Article […]

Earth Satellite Orbits

The fundamental nature of Earth Satellite Orbits Satellites have been there enhancing radio communication for several decades. An understanding of Earth Satellite Orbits is crucial to optimizing the use of communication satellite resources. Radio amateurs were quick to start using satellites for communication. Since the early 1970s, serious efforts were made to put amateur radio on the satellite map. Most earth satellites for amateur radio have been placed in Low Earth Orbit (LEO) with some of them being in sun-synchronous polar orbits. I have been actively working through amateur satellites ever since the early days of OSCAR-6 and OSCAR-7 while I was in engineering college… There have been a few exceptions to the LEO satellites for amateurs. For instance, OSCAR-9, 10, and 13 were phase-3 satellite originally designated as P3A, P3B, and P3C respectively. They were meant to operate in a highly elliptical orbit with a high apogee to perigee ratio. Typically the apogee was planned to be around 36000 Km with the perigee around 2500-4000 Km. OSCAR-9 suffered a launch failure while OSCAR-10 was a partial success. OSCAR-13 did... Click Here to Read Full Article […]

Solar Activity and Ionosphere

Solar activity and its influence on Ionosphere The most exciting and intriguing aspect of radio propagation is Solar activity leading to the creation of the Ionosphere on earth. The entire universe including our Solar system presents us with countless gigantic physical phenomena that continually occur on a real-time basis. In our planetary system, the Sun is the focal point that influences almost all aspects of our life on earth. In this article, we will briefly focus on some of the mysteries of mother nature that make HF radio communication possible. Without these effects that determine how the upper atmospheric structure of the earth is shaped, not only would the HF radio have been non-existent but perhaps there would have been no life on earth. Our sun is a very large celestial body acting as the central pivot of our solar planetary system. It is a continuous source of energy that reaches all planets. The energy released by the sun is multi-faceted and wide-spectrum. This includes electromagnetic radiation across RF, heat, light, X-rays, etc and also sub-atomic particles including electrons, protons,... Click Here to Read Full Article […]

HamSphere 4

Real vs HamSphere Virtual vs Hybrid Radio communication and Amateur Radio as the terms suggest, clearly define the mode of communication using electromagnetic (EM) radio frequency waves. Hence it is obvious that the medium of signal transport must be able to propagate EM waves and not electrical RF energy. There is a clear distinction between the two. EM wave propagation relies on a self-sustaining propagation mechanism by continuous and alternating transfer of energy between an electric field and an associated orthogonal magnetic field. Each of these energy transfer processes generates a new EM wavelet which continues to propagate. In contrast, electrical RF energy uses an electrically conductive medium like copper wires similar to transporting energy at other frequencies including the well-known utility power distribution networks. We may also use fiber-optic medium by modulating a light source with information which propagates over a graded density refractive index medium within the confines of the optical cable. But this too is not Radio propagation. Virtualization is the process of replicating the behavior of a physical real-world process using mathematical modeling, whereas Hybridization is... Click Here to Read Full Article […]

CW & Digital

Fascinating world of CW, SSTV and Digital Radio Since the advent of radio communication in the late 19th century, it has made rapid progress in technology over the passages of time. EM waves propagated between two distant locations. Originally it was CW (Morse code) that was used as a method to carry meaningful information over radio waves. Of course, Radiotelephony and Digital Radio modes were developed later. By itself, in its own native steady-state form, EM waves do not carry any information and hence it is not of much use. We need to superimpose information by using cleaver means to ride on the EM waves (Radio Waves). This is accomplished by a process of modulating the radio wave. Therefore the plain radio wave is the carrier (or a carriage like a horse-cart). Unless some cargo (information modulation) is placed on the carrier (the carriage), the whole exercise of radiating and propagating radio waves between two distant locations is pointless. CW and analog radio-telephony speech modulation like AM, FM or SSB played a predominant role during the first 100 years of... Click Here to Read Full Article […]

How vital is Antenna Polarization in Radio Communication?

Antenna Polarization in Radio Communication What is the significance of antenna polarization in radio communication? Or, should we ask, how does the polarization of radio waves affect radio communication capabilities? We surely need to understand the fundamental concepts and find out the probable practical effects. By-and-large, most of the antennas that we use on a regular basis are linearly polarized and hence produce linear polarized radiations. Although there are several types of antennas that produce circular (LHCP or RHCP) polarization, they are relatively rare in terrestrial communication application scenarios. Satellite-based radio communication often uses circular polarized antennas both at the satellite and the earth station end of the links. However, that’s a story for another day… Or else, check out the article Amateur Satellite Communications. Moreover, the circular polarization throws up its own set of challenges related to polarization rotation directions. As amateur radio operators, generally engaged in terrestrial radio communication, we normally use linear polarized antennas. This is applicable to both HF as well as VHF/UHF communication. Typically, our antennas are oriented in ways to favor either Vertical or... Click Here to Read Full Article […]