Wire Antennas

HF Wire Antennas – A Primer When we speak about wire antennas, the first and foremost thought that comes to mind is the 1/2λ Dipole antenna. This is indeed a classic antenna that is not only used extensively by HF amateur radio operators but also by the shortwave broadcasters and various HF commercial radio communication stations around the world. Of course, there are a variety of other types of wire antennas not only mono-banders but multi-banders too. Most of these antennas are low cost while being easy to fabricate and deploy. The performance of wire antennas for HF terrestrial radio communication is also rather good and cannot be dismissed as trivial antennas. Most wire antennas are horizontally polarized due to their physical orientation. Although the surface wave (ground wave) range of these antennas is lower than the vertically polarized ones on account of horizontal linear polarization, the fact of the matter is that they leverage the properties of the ground (earth’s surface) underneath to provide excellent performance characteristics which are suitable for sky-wave ionospheric skip mode long distance (DX) propagation... Click Here to Read Full Article […]

Yagi Antennas

How do Yagi Antennas work? A Yagi-Uda antenna popularly known as the Yagi antenna is perhaps one of the finest inventions ever made in the field of antennas that revolutionized the world of radio communication. In the year 1926, prof. Shintaro Uda and prof. Hidetsugu Yagi of Tohuku Imperial University, Japan did pioneering work and created the concept of beamforming of antenna radiation by utilizing parasitic elements placed in close proximity to the radiating element. This concept was further refined by the work of countless people over the years but this path-breaking antenna structure was dedicated to prof. Yagi and prof. Uda. Hence we have called this type of antenna the Yagi-Uda antenna or more popularly as the Yagi antenna. Perhaps, we all know that a Yagi antenna provides a unidirectional radiation lobe pattern and enhanced forward gain in comparison to a dipole. However, some might ask, what is the unique concept that makes a Yagi antenna tick? What makes it distinctively different from other types of antennas? … Fair question! We will try to examine some of the fundamentals... Click Here to Read Full Article […]

Omnidirectional Antennas

Introduction to Omnidirectional Antennas In the literal sense, an Omnidirectional antenna is an antenna that radiates uniformly in all directions. However, in reality, the term Omnidirectional needs to be taken in the context of the communication application scenario. For instance, for an antenna in free-space like an antenna onboard an LEO satellite, one might expect it to radiate uniformly in all directions in 3D space, whereas, for terrestrial HF station it would be expected to radiate uniformly in all directions (360°) around the azimuth (horizontal plane). In yet another scenario of a ground station antenna for LEO satellite use, one would expect an omnidirectional antenna to not only cover 360° in azimuth but also at all elevation angles above the surface of the ground thus producing a hemispherical dome-shaped radiation pattern above the earth. Omnidirectional antenna classification is not based on any specific antenna design structure but is classified on the basis of the radiation pattern it creates. Based on the above introduction, one might expect the magnitude of gain in the desired directions would be perfectly uniform but that... Click Here to Read Full Article […]

Do Digital Modes like FT8 work Below Noise?

Digital modes like FT8 work below Noise? – A myth It is a common myth that narrowband digital modes like FT8, JT65, etc establish communication with signals that are below the noise floor. This myth has by and large been perpetuated among the amateur radio community where many operators consider it to be a magical property of these digital modes. These narrowband digital mode signals may not be audible on a regular radio receiver or may not be visible on the band-scope spectrum or waterfall displays of our transceivers but there is nothing magical about it. They certainly do not work with signals being below the noise floor. Barring a few modulation modes like the Spread Spectrum, including both direct Sequence Spread Spectrum (DSSS) and the Frequency Hopping Spread Spectrum (FHSS), typically most other commonly used digital modes need signals to be above the noise floor with a positive magnitude of Signal-to-Noise Ratio (SNR). Spread Spectrum due to its nature, has a very low signal density that typically lies below the noise floor. Hence, it is difficult to detect and... Click Here to Read Full Article […]

To invest in better Radio Rig or better Antenna

Choice between a better Radio or a better Antenna What should I focus on? Should I invest more in a better Radio Rig or a better Antenna? What is it that will provide me better communication prospects and more Dx? These are some of the most common questions that have plagued the minds of new entrants to the hobby of Amateur Radio. Unfortunately, it is equally true that having been swayed by the glamour of well-advertised jazzy-looking modern radio rigs, many of these people have made wrong choices. Only to have learned about their mistake the hard way after having spent a lot of hard-earned money that never really paid dividends as per their expectations. Ironically, even many of the extra-class licensees, in haste to conquer the world, had skipped doing due diligence or ignored sane advice from others who knew. They often ended up making reckless decisions and wrong choices. The answers to the questions that we raised at the beginning are unambiguously clear and straightforward. Yet, at times, amongst a section of radio amateurs, there seems to be... Click Here to Read Full Article […]

Log Periodic Dipole Array (LPDA)

Log Periodic Dipole array (LPDA) The Log Periodic Dipole Array, popularly known as the LPDA antenna, belongs to a broader family of Log-Periodic antennas. Other than the LPDA, various types of Log-Periodic antenna array structures are available. Some of them are the Log-Periodic Tooth, slot, PCB micro stripline, etc. These variants are most suitable, due to their physical structure, for use at microwave frequencies. The concept of the Log-Periodic array was initially conceived in the year 1958 by two researchers at the University of Illinois in the USA. In this article, we will, however, focus mainly on the LPDA is its classic configuration along with several other offshoot derivatives. The LPDA is used extensively for HF, VHF, and UHF radio communications. The distinctive feature of the LPDA in comparison to other well-known antennas like the Yagi, Cubical Quads, etc is that unlike the other two, the LPDA features a very broad bandwidth characteristic. Physical the LPDA might appear to look more-or-less similar in structure to the Yagi, with multiple dipole elements on a boom with progressively reducing element length in... Click Here to Read Full Article […]

HF Surface Wave Propagation (Ground Wave)

HF Radio Surface Wave propagation (Ground Wave) Surface Wave propagation and coverage on the HF radio bands is well known to radio amateurs. Especially, on the Lower frequency HF bands called the Top Bands which includes the 160m band, though it’s technically an MF band. The surface wave propagation phenomena (also loosely termed as a Ground wave) plays an important role in supporting regional short-distance communication with a very high degree of reliability and robustness. Surface wave helps in filling the deaf region, if not fully at least partially that is created around the transmitter location. A region with a radius of typically several tens or hundreds of kilometers around the transmitter forms the skip-distance caused due to the ionosphere not always being dense enough to be able to return reflected (refracted) signals when they approach it at high angles of incidence. Those who might like to brush up the concept of a Skip-zone and Skip-distance could read through my post on the subject Skip Zone – HF. Although most of us have an intuitive understanding of the basic concept... Click Here to Read Full Article […]

RF Testing

Do we need T&M Equipment for RF Testing? Test and Measurement popularly called T&M which form the core of RF testing is perhaps a very vital aspect in amateur radio, as well as in all other disciplines of science and technology. Quantitative evaluation, profiling, characterization, and parametrization of scientific phenomena and engineering system attributes is the single most important aspect. Without T&M, science, and technology would be crippled. Electronic T&M has rapidly proliferated into all disciplines by replacing other non-electronic methods. The latest developments in electronic transducers and sensors coupled with advancement in modern Digital Signal Processing (DSP) and Micro-controller technologies have made RF testing of radio rigs feasible. I have spent a good part of my professional career designing and developing all kinds of professional T&M products and could go on and on. However, what is important for amateur radio operators is RF Testing and Measurement in context to radio communication. We will focus on that. Measurement FundamentalsRF Testing and Measurement fundamentally require an understanding of basic principles of electrical networks, their analysis and design concepts. This would minimally... Click Here to Read Full Article […]

Are HF Bands Really Dead during Low SSN at Solar Cycle Minima?

Low SSN Solar Cycle minima – HF bands dead? Too often we hear amateur radio operators complain about HF bands being dead during the low ebb of a solar cycle that causes low SSN. Really? Who says the bands are dead? Think again… Let us do a reality check. At the time of writing this post, it is November 28th 2019. We are passing through the cusp between solar cycle #24 and #25. The solar activity is at its rock bottom. The ionization density of the ionosphere is at a dismal low. Does it make HF radio propagation a challenge? Yes, it does… But it does not mean that the bands are dead?… Not Really. What really happens during the low SSN conditions is that HF band propagation openings that used to happen frequently are now less frequent. The duration of these openings to a particular DX destination becomes shorter. The strength of band openings becomes shallower. However, none of these means that the bands are dead or there is no propagation. All it means is that now HF DXing... Click Here to Read Full Article […]

Will low SWR always ensure a good Antenna setup?

Does Low SWR always mean a good Antenna setup? Many amateur radio operators often assume it to be true but the question is, will low SWR always ensure that the antenna has been optimally setup? Although a low SWR on the transmission line to the antenna is certainly welcome, the question still remains whether it conclusively indicates a healthy antenna system setup? contrary to popular belief, No, not always… There are various other factors that go a long way in determining optimum antenna performance. This is notwithstanding the fact that the location of antenna installation, its surroundings, and height above ground play vital roles. Let us ignore these limiting factors because I know that most of us, the radio amateurs, are often constrained by real-estate limitations and therefore may not always be able to install our antennas the way we might have liked to. Within the realms of the above-cited limitations, the SWR is still not the ultimate indicator of antenna system health. Let us examine why is it so, and what are the other factors that could overshadow the... Click Here to Read Full Article […]