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 […]

Interpretation of S-Meter Noise Floor in HF Radio Receivers

S-meter Noise Floor in HF Radio Receivers In this article, I will focus on the interpretation (or perhaps misinterpretation) of the S-Meter Noise Floor levels as they prevail on HF radio receivers of typical transceivers used by amateur radio operators. Over the past year, I have covered various aspects of the difficulties that are often faced while negotiating propagation conditions on the HF radio bands. This is especially true during the current bottom phase of the Solar Cycle as we make the transition from cycle #24 to #25. This phenomenon is expected to persist for quite a while more, and therefore our discussions will continue to be quite relevant for a long time. Even later, during the healthy part of the upcoming solar cycle, the measures that we take now will continue to let our optimized radio stations perform far better than the non-optimized stations of many of our peers. Through a set of several articles, I have tried to place on the table various pitfalls of working HF DX under these conditions as well as offered various solutions to... Click Here to Read Full Article […]

Watch Radio Modulation Depth for best Signal Clarity

Set Radio modulation Depth for optimum Clarity For the sake of optimum clarity and intelligibility of radio transmission, the radio modulation depth must be controlled by ensuring that the microphone input level is maintained well within the automatic Level control (ALC) correction range of the modulator. Failure to do so would result in the introduction of audio distortion. Overdriving the modulator will invariably result in the creation of unwanted AF harmonics and spurious products. Consequently, the intelligibility of the demodulated audio on the receiver at the DX end will also suffer proportionately. Several ill-effects of overmodulation will begin to surface. In extreme cases, the overmodulating radio station will begin to splatter across the band. However, with the modern radio transmitters, sideband splatter is usually not the problem. Nonetheless, this could have been a huge problem in earlier transceivers because it would have produced spurious RF components across a significant portion of the band. At times the splatter could have extended across the entire band. This kind of slatter from just one operator might have rendered the band more-or-less useless for... Click Here to Read Full Article […]

Propagation

Understanding Radio Propagation The study of principles of propagation of electromagnetic waves and acquiring a reasonably good working knowledge of radio propagation go a long way in enhancing the quality of on-air experience for any amateur radio station operator. It is a complex subject where many variables of nature come into play. Radio frequency spectrum is extremely wide, starting at ELF, VLF, LF and going all the way through MF, HF, VHF, and UHF into the upper microwave spectrum, L, S, C, X, Ku, K bands and beyond. The propagation behavior through various mediums at different frequency bands varies drastically. As amateur radio operators, we are mostly concerned with MF, HF, VHF, UHF, and lower segment of the microwave spectrum. Most challenging of all these is HF radio propagation. HF radio propagation is influenced significantly by several exogenous factors like seasons, Geo-magnetic field variations, normal solar activity, and transient coronal ejections from the sun. Not only the fundamental principles but also the ability to reasonably forecast propagation possibilities based on various geophysical parameters and solar radiation data metrics is important.... Click Here to Read Full Article […]

Challenges of working HF DX near Antipodes

Working HF DX stations located near Antipodes Working HF DX at the longest possible physical distance on earth is often referred to as working stations near Antipodes. These situations present several unique challenges that may never be observed while working regular DX at shorter distances that are not as far as the Antipode. These challenges manifest themselves while using directional beam antennas and may not be observed or appreciated by those of us who have omnidirectional antennas. The challenges of working stations at or near the antipodes are not only experienced by the station holding the frequency and calling CQ but also by those who are trying to work him. We cover the concept of Antipodes in an article under the section Geodesic for Terrestrial HF Radio. However, to recap for those who might be new to the term, an Antipode is a location that is at the opposite side of the globe from where a station might be located. Hence, every operator has a unique antipode based on his location. For the sake of simplicity, if we assume the... Click Here to Read Full Article […]

Radio Systems

Fundamentals of Amateur Radio Systems Take a look at some of the fundamentals of the amateur radio system. Technologies related to radio systems for communication have developed rapidly over the last seventy-five years or more. World war II was the turning point. Even prior to that, amateur radio operators were at the forefront experimenting, working with new ideas, and developing new methods of modulation to increase transmission efficiency. With limited resources in terms of transmitter power and the hunger to reach further and further brought about the concept of SSB radio. Initially, it was not taken seriously by the commercial world who continued to use the time tested AM. Eventually, the merits of SSB stood so tall that it could no more be ignored. Now almost entire HF radio communications whether military or commercial radio systems are all done with SSB. This was followed by big developments in VHF/UHF and microwave technologies. The advent of satellites opened up new avenues and satellite-based communication systems become a vital cog in the giant wheel of radio systems communication. Genesis & Evolution of... Click Here to Read Full Article […]

Learn CW Morse Code – Lesson Set 2

Learn CW Morse Code – Lesson Set 2 This is Lesson Set -2 in our multi-part series of CW Morse Code hands-on tutorials where we will introduce numerals and a few important punctuation marks as per International Morse Code standards and as approved by IARU for Amateur Radio Service use. While pursuing the previous Lesson Set – 1, you would have, by now, learned to copy all the 26 English language alphabets by the ear. You would have attained a proficiency level that would allow you to copy all the alphabets at 20 WPM with a Farnsworth timing of 17 WPM. Do not worry about the slight Farnsworth timing delay that we continue to retain at this stage of our learning process. Later, in Lesson Set – 3, we will gradually normalize the transmission speed which will be done in a seamless and painless manner. If you now intend to continue with this Lesson Set – 2, I would request you to pause for a moment and honestly make up your mind that you are ready to do so… You... Click Here to Read Full Article […]

Global HF Radio Propagation Openings – The Summer of 20

HF Radio Propagation Outlook – The Summer of 2020 In the Summer of 2020, the HF Radio Propagation openings are not so frequent as one would expect under normal circumstances. The reason, as we all know is on account of the phase of the 11-Year Sunspot Cycle that we are going through at this time. The 24th Solar Cycle has ended while the 25th cycle has yet to pick up steam. We are placed at the cusp, which appears like a deep broad valley when observed on a graph. As a consequence, the prevailing SSN is either extremely low or zero (0) most of the days. The 10.7cm Solar Flux Index (SFI) is also near the rock bottom. The solar magnetic activity, as well as the energy and particle ejections, are rather placid and limited. For our friends living on the Southern side of the Equator, the phrase, Summer of 2020, may not sound right because it is the winter for them. I totally acknowledge this reality but would request them to bear with me on this matter with regards... Click Here to Read Full Article […]

Impact of VHF-UHF Radio Repeater Site Location on Coverage

VHF-UHF Radio Repeater Site Location vs Coverage The significance of VHF-UHF radio repeaters’ site location for achieving the desired reliable coverage range cannot be taken lightly. Adequate due diligence is required in terms of assessment of the topology of the territory to be covered. A radio repeater site that is located on a high elevation geographic feature would usually provide a technically viable option. Of course, the physical logistic viability of the site is also equally important. Some geographic features might be technically excellent but might be difficult to access and hence might not be logistically viable. Therefore, site selection is often a tricky process that could require a lot of thought. Needless to say, depending on the topology of the land, at certain places, the best choice of a radio repeater site might be obvious and quite intuitive. For instance, a city with a hill on the outskirts that is visible from all across the town would be an ideal choice. Similarly, a suburban or rural area on a plain terrain could be served sufficiently well by a radio... Click Here to Read Full Article […]

EMI-RFI and Noise related HF Radio Station performance loss

EMI-RFI and Noise related HF Radio Station performance loss HF radio performance loss due to EMI-RFI and noise in and around the station environment is often a major issue that could almost cripple the communication capability. This is especially true during conditions of low SSN, the way it prevails during the ebbing part of the Solar Cycle. Many amateur radio operators do not realize the real consequences and the utter magnitude of loss in their radio station’s performance. More often than not, we have heard statements like – The HF bands are now dead at low SSN, the only viable way is to work HF using FT8, SSB radiotelephony is hardly possible during low SSN conditions, I think I need to invest in a linear HF power amplifier, etc, etc… – We have heard all this far too often. However, it is not necessarily the whole truth. We all agree that during low SSN conditions, negotiating the HF radio bands become more difficult and stringent in comparison to what happens during the better part of the Solar Cycle. When the... Click Here to Read Full Article […]