Archive for 2019

HF DX near Antipodes

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 […]
Digital mode FT8 noise levels

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 equally difficult... Click Here to Read Full Article […]
HF Long Path LP

HF Long Path (LP) – Quick tips and pointers

HF Long Path (LP) – Getting acquainted HF radio DXing may often be leveraged by the use of HF Long Path (LP) from time-to-time. By-and-large, on a routine basis we all tend to explore HF radio propagation openings that prevail along the better known Short-Path (SP). The earth is nearly a spherical object and the path taken by the radio signals to travel to the DX location is always via the shortest straight path along the spherical surface of the globe. However, this straight path if extended beyond the DX location eventually circles the globe and reaches back to the originating TX station’s location. This is the full Great Circle path. The Great Circle round-the-world path is always unique between any two radio stations on earth. In one direction along the circular path (Great Circle), the distance is shorter than the distance along the opposite direction. The direction along the shorter of the two distances is called the Short Path heading, while that in the opposite direction is the Long Path heading. There is only one exception. It is when... Click Here to Read Full Article […]
8-el yagi antenna bearing for HF DX

Need We Fuss About Exact Antenna Bearing for HF DX?

Do we need to set eaxct antenna bearing for HF DX? While working distant stations on HF bands do we need to be fussy about the exact beam headings and antenna bearing for HF DX? The short answer is NO… Yet, with the availability of various software utilities available to us both as standalone applications or online services, we often tend to get carried away. Several amateur radio operators, unfortunately, believe that unless their directional antennas like the Yagi are pointing precisely at the DX location they would not receive optimum signals. This is far from the truth. Let us quickly examine why. Of course, what we are discussing here is notwithstanding the fact that for VHF/UHF terrestrial radio contacts across several tens of kilometers one would need to beam quite accurately. Not only because the beam flare-out is narrow at short distances but also because much higher antenna gains on VHF and beyond produce far narrower beams… However, right now, we concern ourselves only with HF antennas for DX contacts. People at times ask me, What is your Grid-square?... Click Here to Read Full Article […]
HF band low SSN propagation

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 the 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 become shallower. However, none of these means that the bands are dead or there is no propagation. All it means is that now HF... Click Here to Read Full Article […]
PSK31 Waveform

PSK31 – A Robust QSO

PSK31 – for exciting HF band QRP PSK31 like most of the other narrow-band digital text communication modes requires very little TX power into a very modest antenna. PSK31 is also quite immune to co-channel interference by voice modulated radio-telephony signals due to the nature of the spectral distribution of human voice. Although PSK31 is a popular mode, many operators have failed to appreciate the inherent merits of this modulation mode and often resorted to incorrect modulation settings, higher than necessary TX power, or the use of large antennas which effectively increase the ERP beyond what is required for effective and sustainable PSK31 communication. This is a demonstration of typical QRP QSO using 5W (perhaps it was 3-4 W) into 1/4λ vertical ground plane antennas used at both ends of the circuit. The distance was approximately 5800Km between a station with the QTH in Sweden and my QTH in New Delhi, India. The QSO was conducted on the 17m band at a little after 14:30 UTC. The PSK31 signal was not visible on the band-scope of my transceiver but was... Click Here to Read Full Article […]
HF Skip Zone

Skip Zone – HF

Beware of Skip Zone while working HF radio A good radio amateur friend of mine from Poland sounded quite anxious when he told me that his new antenna was behaving peculiarly. He was afraid that being a restricted size vertical antenna perhaps it was not performing as it should. He asked for my views. After speaking to him I realized that there was nothing wrong with the antenna but the problem was entirely different. The issue that my friend was facing was a typical ionospheric skip zone situation. Although on the 20m band, he could work stations in Moscow, various parts of Italy and Spain which are all quite a distance away, he was unable to copy or work into nearby countries like Germany, Netherlands, Czech Republic, etc. I soon realized that in his hurry he had completely forgotten to account for the prevailing “Skip Zone” around his QTH. All of us make such mistakes and then scratch our head over inexplicable results. For those who would like to visualize what was happening on the 20m band from the location... Click Here to Read Full Article […]

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