Johnson's Techworld

 Oscillator in electronics is a circuit which produces periodic oscillations or alternating signal which could be a sine wave, square wave or another type of wave. The oscillator is powered by a direct current source and can be used in a wide variety of applications like radio, television, computer and mobile phone. In the animation, a resistor-capacitor (RC) network is used to feed a portion of the output of the inverting Schmitt trigger into its input. Schmitt trigger is a circuit with hysteresis implemented by applying positive feedback to the non inverting input of a differential amplifier. It is called a trigger because the output retains its value till the input changes sufficiently to trigger a change. That brings us to the most common form of linear oscillator or harmonic oscillator in which a transistor or operational amplifier is connected in a feedback loop with output fed back into its input through a frequency selective electronic filter to provide positive feedback. In

 I have been hearing about the low noise level for loop antennas for a long time and always wanted to try out one. Two problems faced by me were the limited space available at home and the lack of a 4:1 matching transformer needed for a delta loop antenna. After a long period of brainstorming, I decided to try out a 2m full wave loop antenna as that is the one which can easily fit in on my small first floor terrace. An online search brought me straight to the Full-Wave Loop Antenna Length Calculator . There is a lot more information on that page than just a calculator for the length of the antenna. It has been mentioned that even though a circular loop is ideal, squares, triangles and other shapes also can work well, provided you make the area enclosed by the loop as big as you can. That sounded nice and gives option to experiment with multiple shapes. A full wave loop can be used on frequencies higher than the design frequency as well. So I can use a 2m loop for 70cm when I am trying

 One of the important uses of transistors in electronic circuits is as an amplifier, though there are other uses like in switching, oscillators and frequency changers. Amplifiers are devices which can amplify weak signals and make them strong signals. Different types of amplifiers are used in radios and audio devices. Amplifiers used to amplify very weak signals and provide a drive to power amplifiers are known as pre-amplifiers. Power amplifiers are the output stages which provide large audio or radiofrequency signal outputs. Power amplifiers are classified into class A, B, AB and C amplifiers, depending on the region of the characteristic curve of the transistors at which they operate. Each type has a different application in electronics. While these classes are for linear amplifiers, there are also class D and E for switching designs. Classification of the linear designs are based on the time period during which the active amplifier device is passing current, expressed as a fraction

  My earlier attempts at checking in to morning SSB HF nets on CW were unsuccessful as I could not setup my FT-710 radio to TX on CW while listening on SSB. I had posted this problem online and couple friends suggested using split mode with different VFOs to work SSB and CW. The problem which I was facing was that the keyer would not switch on when SSB mode was selected. So split mode would sort out that problem. Initially I tuned both VFOs to the same frequency 7.12345 MHz for VU2VWN Memorial Net. Not sure whether it was because of that or due to some other technical reason, net control did not hear me in the first attempt. Then I tried with the TX VFO on 7.123 MHz and I was heard. My CW was far from perfect because I have very little practice with the keyer and of course I was a bit nervous while checking in to the HF SSB net for the first time. I had checked in to CW nets on 40 and 20 m once or twice, again with plenty of mistakes as usual!

 Though I have worked several stations from Europe during the past 10 months with my new FT-710 radio, I had to wait for the CQWW DX Contest 2024 to have the first station from England in my log. That happened today morning, when the contest was about to be over. I could hear M6T nicely on 14.2575 MHz and after a few calls I could have them in my log. Looking at their QRZ.COM page, they have a fantastic station, setup by Bob Carpenter, G4BAH, who sadly passed away in August 2016. 

 Unlike direct current, alternating current reverses direction of flow periodically. Rectifier is a device which converts alternating current to direct current. It does this by cutting off one of the half cycles of an alternating current so that it becomes a pulsating direct current, flowing only in one direction. In the earlier era, vacuum tube diodes were used as rectifiers. Now there are semiconductor diodes which are commonly used in hobby electronics. Other types of rectifier devices are mercury arc valves, stacks of copper and selenium oxide plates and silicon controlled rectifiers. Rectified output needs smoothing out of ripples using high value capacitors and inductors. Voltage regulation is done by devices like zener diodes, to provide a stable output in the face of potentially fluctuating loads as in amateur radio transceivers. Transceivers need high current during transmit mode and only very low current during reception of radio signals. One disadvantage of half wave rectifi

 In spite of a solar flare yesterday and band predictions being just 'fair' as per the Solar Terrestrial Data on QRZ.COM, 20m band is open here early morning. Could be something like grey line propagation. I could see several strong signals on the waterfall display of my FT-710 radio, though there was fading (QSB), with signals moving from 5,9+20 dB to 5,9, with basic noise level at 9+. Still I could work TO7K on 14.203 MHz at 4.55 am IST (UTC+5.30). Here is the recording of the station just before I had the contact, coming here nicely.

 Electronic components like resistors, capacitors and inductors can be connected together in series or parallel. Components connected in series are connected along a single electrical path and same electric current passes through each of the components, which will be equal to the current through the network. Voltage across the series network will be equal to the sum of voltages across each component. On the other hand, when components are connected in parallel, they have multiple current paths and each component has the same voltage across it, which will be equal to the voltage across the network. Current through the network is the sum of currents through each component. Circuit with only components connected in series can be called a series circuit and a circuit with only components connected in parallel is called a parallel circuit. Most electronic circuits will have a combination of series and parallel circuits. As we have seen earlier, when resistors are connected in series, the to

 2024 CQ World-Wide DX Contest for SSB mode starts at 00:00:00 UTC Saturday, 26th October 2024 and ends at 23:59:59 UTC Sunday, 27th October 2024. Even though I am not a contester sitting through out the night to get contacts, I am always happy to see a contest on the air. It lights up the waterfall display on my FT-710 with plenty of stations. I am able to see a few simultaneous waterfalls only on 40 m during morning net times when we have 5 nets and a few other rag chews. On all other bands and at other times, it is only an occasional signal on the waterfall. On contest weekends, there is plenty of activity on most of the bands and I get to work some new stations. That is why contests are important for us even if one is not a contester. I did participate actively in the Garden City Contest long back and won a third position in CW category, with my homebrew radio. CQ WW DX SSB contest is on six bands only: 1.8, 3.5, 7, 14, 21 and 28 MHz. Of these, I do not have an option for 1.8 and

 Phase of a wave is the angular displacement of a sinusoid from a reference point or time. Phase in the context of alternating current can be considered as corresponding to the angular position of the armature in the AC generator. Armature is the part which generates an electric current when it rotates in a magnetic field. Armature is made of a coil of wire wound around an iron core. Instead of the armature rotating, magnetic field can be made to rotate by rotating the permanent magnet which produces the magnetic field. The term phase is also used to denote the live wire in home electrical wiring. Usual large generators generate alternating current with three phases so that three lines run along the high tension and low tension supply lines in addition to the ground or neutral line. Simplest way to generate three phase alternating current is by having three sets of coils in the generator, physically offset by an angle of 120 degrees to each other, which is one third of a complete 360 d

 Basic electronic components can be divided into passive and active components. Passive devices are resistors, capacitors, inductors and transformers. Active devices are diodes and transistors. Integrated circuits are combinations of large number of transistors, diodes, resistors etc, in a single package. Basic properties of these devices and some simple practical exercises which you can try out easily are included in this session and will be very useful for anyone interested in learning electronics as a hobby.

 While direct current flows only in one direction, alternating current changes direction with a periodicity. Typical mains supply in this region has a frequency of 50 Hz or 50 cycles per second. That means a change in direction of flow of current 50 times every second. That is the frequency of the alternating current in the mains supply. If the instantaneous values of current and voltage are plotted on a graph against time elapsed, it is seen as a sinusoidal or sine wave pattern. Sine wave form is used in power transmission because that leads to the most efficient transmission of energy. Inexpensive power inverters for converting direct current to alternating current may use square waves. Time taken for completion of one cycle is known as the period and will be the inverse of the frequency. Wavelength can be determined if the velocity with which the wave travels is known. Though we do not usually calculate the wavelength of mains supply, wavelength is an important parameter of radio wa

 Metals like iron, nickel, cobalt and some of their alloys can be attracted by magnets while those like copper, manganese and aluminium are not. A magnetic bar has North and South poles and they will orient in North - South direction if suspended in the air. That is because of Earth's magnetic field, which also has a North and South pole, though they do not exactly correspond to the location of geographical North and South poles. Like poles of magnets repel each other while unlike poles attract each other. There are invisible lines of magnetic force surrounding a magnet which decrease in strength as the distance from the magnet increases. They constitute the magnetic field surrounding the magnet. Similarly, Earth also has a geomagnetic field, which is very important in radio communications. Geomagnetic storms resulting from sudden spurts of solar activity can disrupt radio communications globally, as we had in May 2024.  Iron, nickel, cobalt and some of their alloys are ferromagne

  C21MM, the German DXpedition to Nauru Island , is from October 10-29, 2024. Just a week more, have you got them in your log? Well, I have not been able to hear them yet. QRZ page of C21MM has a whopping 291,230 lookups as of now. That shows how popular the DXpedition is among the amateur radio fraternity. They are a dedicated team of 14 operators from Germany. Nauru island, formerly known as Pleasant Island, is an island nation in Oceania region in the central pacific, officially known as the Republic of Nauru. VOACAP HF Propagation Predictions for C21MM, October 14-27, 2024 is available on the DXpedition website. If you enter your grid location, a lot of charts are generated by the program. But you need a lot of experience in interpreting them, which unfortunately I do not have! Logsearch powered by CLUBLOG is also there as well as an option for OQRS, for which you have to wait until the end of the expedition. Operations are planned on all bands from 160 m to 6m. CW, SSB, RTTY and

 The ability of a conductor to allow free flow of electrons can be termed as conductance. It is the reciprocal of resistance and unit was called mho , which is ohm spelled backwards! Symbol was inverted ohm sign: ℧. Conductance G is the inverse of resistance. If R is the resistance of a conductor, G is 1/R mho. In the International System of Units (SI), the unit of electric conductance is siemens , represented by the symbol S. Siemens is also the unit for electric susceptance (reciprocal of reactance) and electric admittance (reciprocal of impedance), which were also represented by mho . Though the symbol is capital S, the name of the unit begins with lower case letter s! It has been mentioned that the SI term siemens  is used universally in science and often in electrical applications, while  mho  is still used in some electronic contexts. As discussed earlier, the property of a circuit or a component that opposes a change in current is inductance. Inductance is represented by L and

 Conductors are used in electronic circuits to carry electric currents between various parts of the circuits. Insulators are used when you do not want currents to get conducted between adjacent components in a circuit. The printed circuit board on which electronic components are mounted have both conductors and insulator. The basic material with which the PCB is made is an insulator with very low conductivity of electricity. The circuit printed on it has high conductivity and is usually made of metals like copper. The insulator between plates of a capacitor is known as a dielectric. Sometimes the dielectric is air, which is also a poor conductor of electricity under usual operating voltages. At high voltages, especially if the distance between conductors is less, air can get ionized and act as a conductor, producing arcing. You may have noted this in high voltage overhead lines sometimes. Current flow through a conductor is measured using an ammeter, which is connected in series. The u

 Kirchhoff's circuit laws are two equalities that deal with the current and potential difference or voltage in electrical circuits, described in 1845 by German physicist Gustav Kirchhoff. Interestingly, this year corresponds to the two-hundredth birth anniversary of Kirchhoff! According to Kirchhoff's Current Law, total current entering a junction in an electrical circuit is equal to the total current leaving the junction. Kirchhoff's Current Law is also known as Kirchhoff's first law or junction rule. It is based on the conservation of charge principle which states that electricity is neither created nor destroyed as it flows through a circuit. Kirchhoff's Current Law is considered while designing and analyzing circuits, troubleshooting and repairing circuits. If currents entering a node is assigned positive values and that exiting it negative values, according to Kirchhoff's Current Law, the algebraic sum of all currents entering and exiting the node will be

 We discussed conductors and insulators earlier. There is another group known as semiconductors like germanium and silicon which are bad conductors of electricity in their natural form. If some impurities like boron or antimony are added in minute quantities to these they can have either an increase in free electrons or a deficiency of electrons. Then they become semiconductors. The process of adding impurities is known as doping. When there is a deficit of electrons, it is called a P-type semiconductor. They have positively charged 'holes' as charge carriers. N-type semiconductors on the other hand have excess electrons as charge carriers. Silicon has four electrons in the outermost shell. When it is doped with boron having only three electrons in outer shell, it becomes a P-type semiconductor, with deficit of electrons or 'holes'. Doping with antimony which has five electrons in outer shell makes it an N-type semiconductor, with an excess of electrons. PN junction is

 Today morning VU2JGA came back to my CQ call on 7065 kHz just after 7 am and told me that he is operating a JOTA station from Pune. May be because it was early morning, I could not hear any scouts and guides from that station. Last year AU2JOTA/VU3YEG was operating a JOTA station on VU2MJJ VHF repeater. It was a JOTA station for Rovers from Thrissur. A few days later I received a special QSL validation card as well. Jamboree on the Air (JOTA) is an annual Scouting event that connects Scouts around the world with the use of amateur radio. The event is held on the third full weekend of October each year, together with Jamboree on the Internet (JOTI). More details can be found on the JOTA-JOTI website . As per the website, JOTA-JOTI 2024 is from 18th to 20th October 2024.  A43JOTA special event station from Oman was operating on 28.400 MHz today evening. We had VU3SIO operating from a school at Kozhikode and VU3YEG operating from Thrissur. VU3KUD had organized JOTA at Kannur. It was a n

 An inductor is simply a coil or loop of wire which opposes a change in the current within it. Inductance of a coil is measured in Henry. Inductance of a coil will depend on the number of turns in the coil, permeability of the medium inside the coil, cross section of the core, and the spacing between the turns of the coil. The more number of turns there are in the coil, higher the inductance. Higher permeability of the core also increases inductance. Coils with larger cross section have higher inductance. In the case of spacing between the turns of the coil, it is the other way round. Smaller the spacing between the turns of the coil, higher the inductance. The inductance in this discussion is actually self inductance of the coil. A change in the current in the coil induces a voltage within it. One Henry is the amount of inductance required for generating one Volt of induced voltage in the coil when the current is changing at the rate of one ampere per second. As in case of capacitance

 Next important passive electronic component after resistor is the capacitor, which can be used to store electrical energy. There are various types of capacitors available in the market like electrolytic capacitors with a thin layer of electrolyte connected to metal plates, capacitors using paper as dielectric, capacitors with air as dielectric and ceramic capacitors. Each one is for a different purpose. There are also capacitors in which the capacitance can be varied, known as variable capacitors, often used in tuning resonant circuits. Capacitance is measured in Farads, microfarads, nanofarads or picofarads, depending on the value from higher to lower. High capacitance in circuits for smoothing out ripples in rectified direct current uses several thousand microFarads. Farad being a large unit, is seldom used. A typical tuning capacitor in radios may be rated at 500 picofarads (500 pF). A capacitor is said to have a capacitance of 1 Farad if it can store 1 Coulomb charge at a potentia

 

 Having gone through the topic list to be learned for amateur radio examination (ASOC) in India, we will start refreshing our memories by revising mostly what we learned at school. Please note that this is for the pleasure of learning and not an official training program. We often call ourselves as 'lifelong learners'! Electronics uses active and passive components to control the movement of electrons. Electrons are tiny subatomic particles seen in all matter, outside the nucleus of atoms. Continuous movement of electrons in a material constitutes an electric current. When there is no continuous movement of electrons, but there is an excess or deficit of electrons in a material, causing it to be electrically charged, we call it static electricity. Materials with free valence electrons in outer shells act as conductors while those without free valence electrons are insulators which do not conduct electricity. In general, metals like copper, aluminium and silver are good conducto

  Usually I don't hear anything on 15m most of the time. Strong Station on 15m After 10 pm tallies with the Solar Terrestrial Data shown on QRZ.COM which mentions good propagation on 15m during day and night.

 To start with, we will go through the list of topics to be learned while appearing for the amateur radio licence examination (ASOC) in India. Most of you will find that many of the topics in Basic Electronics for part A of the exam have already been learned at the basic level at school science classes. We will have to refresh our memories as well as learn a bit more. Radio Regulations in part B of the exam have to be learned in full as that is what we have to follow as an amateur radio operator. First we will have a look at the topics for Restricted Grade examination and then see what are the additional topics to be learned for a General Grade examination. As mentioned previously, we can appear for both exams simultaneously by paying the fees for both examinations so that if we pass at least the restricted level, that level of licence will be granted in due course. Once you start working as an amateur radio operator, it is easier to learn further and clear the next level. This list is

  Amateur radio is a wonderful hobby in which radio amateurs with a valid license in their country communicate using two way radios with amateur radio operators around the world. There are thousands of radio amateurs in India. In some countries there are several hundred thousands of radio amateurs. Long distance communication is possible through short wave or HF communications and through amateur radio satellites. Amateur radio operators render emergency communication support during natural calamities which might destroy regular communication networks. Preliminary details on appearing for the licensing examination in India are covered in this part 1 of the series.

 The concept of antenna aperture is easy to explain if you look at a horn antenna , though it applies to all antennas including a dipole antenna which has no physical 'aperture'. In the figure shown here, the area marked with pink dotted line corresponds to the physical aperture of the horn antenna, where the incident electromagnetic wave strikes in case of a receiving antenna. But the effective area will be the total power received by the antenna divided by the power density of the incident wave. The effective area of the antenna may be less than the physical area of the aperture of the horn. In case of other types of antennas which do not appear to have a physical aperture like, the wire antenna, the effective aperture of the antenna can be found using the same method. While calculating the total power received, the resistive loss in the antenna material will also have to be considered. Power from the antenna is transferred to the receiver as its input power. If this power re

 Efficiency of the antenna is the ratio of power radiated by the antenna to the power supplied to the antenna. Antennas can be very simple dipole antennas or very complex designs like stacked Yagi-Uda antennas or Cross Yagis for LEO Satellite operations . Either way, their basic function is to convert electrical signals to electromagnetic waves and vice versa, depending on whether it is used for transmission, reception or both. Important parameters of an antenna are the gain, directivity, radiation pattern including the angle of radiation and polarization, beamwidth and effective aperture . All these will determine the efficiency of the antenna for a given application. Gain of an antenna is usually mentioned in comparison with the gain of a theoretical isotropic antenna (dBi) with spherical radiation pattern all around or sometimes in comparison with a dipole antenna (dBd). Gain of the antenna will be equal to the product of efficiency and directivity of the antenna. Directivity

  It was the South Jakarta DX Contest 2024 https://sjdxcontest.com/ . The time window was consistent with grey line propagation ! Signals faded within about one hour.

 

 Three main types of configurations in which transistors are used are the common emitter, common base and common collector. While two leads each are needed for input and output of an amplifier circuit, the transistor has only three. So one lead has to be common between input and output. The transistor configurations are named after the lead which is common to both input and output in the given configuration. In actual circuits, there will be resistors and capacitors in addition. Radiofrequency circuits will have inductors and transformers as well. Values of each component will be calculated according to the purpose of the circuit. In all these configurations, the emitter is forward biased and the collector reverse biased. The most common type is common emitter configuration in which emitter is grounded, base acts as the input and collector as the output. So the input is given between the base and the emitter which is grounded. Current gain in this configuration, which is the ratio of c

 Listened to the pass of International Space Station Cross Band Repeater at about 5.20 pm IST (UTC + 5.30) hoping to have some contacts as the SSTV transmission would have been paused for School Contact at Quebec, Canada. It was a Western Pass with about 40 degrees maximum elevation in this region. I could hear my call on the downlink when the satellite was near the time of closest approach (TCA), with my Moxon Yagi pointed in that direction. I could not hear any other station till then. So I went outside and rotated the antenna once again towards the direction of loss of signal (LOS). Soon after returning to the radio, I could clearly hear the NA1SS beacon in CW. So I was happy that there was no problem in my setup. My friends in the region would have been busy celebrating the Pooja Holidays or looking for SSTV transmissions on 145.800 MHz, which is more popular in this region than the cross band repeater! Of course, most of them who are really active would not have waited for SSTV as

 When the last G5 Extreme Geomagnetic Storm occurred in May 2024, I was on 40m and suddenly lost propagation to all the longer distance stations and we could hardly hear nearby stations at about 120 km. Now with a G4 Severe Geomagnetic Storm in progress, and planetary K index in the red, at 8+ range, I could hear couple of local stations on the Silicon City Net at 7088 kHz extremely strong! VU2XPZ at 127.7 km was coming here 5,9+ and he was giving VU3LLL a 5,9+40 dB report. He was wondering what is going on! VU3LLL at 210.0 km was heard 5,9+20 dB here.

 I have always wondered why an air conditioner which runs on alternating current mains power supply is labelled as DC Inverter. I have also seen a sticker on the refrigerator mentioning 'Inverter Compressor". The inverter which I was familiar with was the inverter which is used to power a part of our home wiring when the mains supply fails. That runs on a 24 Volts battery and converts direct current  to alternating current at 230 Volts. Recently I had also heard of solar inverters used to convert the direct current delivered by solar panels to alternating current for the home circuits. In case of inverter air conditioners, there is dual conversion happening, unlike the home inverters or solar inverters. The alternating current supply is first rectified into direct current, which runs an inverter, converting it back to alternating current of variable frequency and voltage. That is how the name came for the compressors of modern air conditioners and refrigerators. Conventional c

  Delta loop antenna is simple to make if you have two high supports or two low supports and one high support. It has directivity along the broad side and a low noise level. 4:1 balun needed at feedpoint could be replaced by a quarter wave 75 Ohms matching section. Multi-band operation is feasible, with and without tuner. Multi-element directional delta loop antennas have been made for higher bands with wider beam width for a given gain than Yagi-Uda antennas.