Johnson's Techworld

 When I checked for Google Trends for Amateur Radio, I found that Yaesu FT-60R Dual Band Handheld 5W VHF/UHF Amateur Radio Transceiver as the top trending topic with breakout results. But when I searched after some time, the top one was IC 7300 and it kept on changing frequently. May be because the total number of searches are not high compared to other search terms on Google. Checked Amazon.com about the availability and found that it is available, but will not ship to my region. I had noted that the interest on Google was mainly from United States of America. I noted Weather Alert as a special feature on Yaesu FT-60R. That may be the reason for it trending in the US. Other features seem to be similar to other dual band handheld radios, with 1000 memory channels and coverage for both VHF and UHF amateur radio bands as well as additional wide band receiver coverage, mentioned as even up to 999.99 MHz. That is just below 1 GHz! That could be another reason why it is popular in the U...

 As most of us are aware, USB is a data transfer protocol which has been revised from the original Universal Serial Bus to the latest USB4, with data transfer speeds up to 80 Gbit/s. Type C is the designation of the connector which you are familiar in mobile phone chargers. Type A plug and socket are the ones you connect with your laptop and type B the one for your printer. A cable to the printer from the laptop will have type A plug at one end and type B plug at the other end. My FT-710 radio uses a similar cable for CAT control or Computer Assisted Transceiver control as well. PD stands for power delivery and the current USB cables are capable of power delivery with rapid charging of devices including mobile phones with varying levels of voltage and current. Original USB devices could deliver only 5 V while the latest ones can deliver even up to 48 Volts and 240W. The white cable is a conventional USB type A to type C cable. The black one is thicker USB-C PD or power delivery cab...

 Radiation-hardened-by-design (RHBD) is a methodology that uses circuit techniques to make microcircuits more resilient to radiation as required at outer space in case of amateur radio satellites. In case of amateur radio satellites, it is more relevant for medium earth orbit and geostationary satellites located at higher altitude. You may remember that GreenCube or IO-117 failed after a good period of operation, possibly due to radiation induced damage. Ionizing radiation in outer space include particle radiation and high energy electromagnetic radiation. On the terrestrial aspect, RHBD devices are needed around nuclear reactors, particle accelerators and during nuclear accidents. Radiation hardening of semiconductor electronic components require some design and manufacturing variations that reduce susceptibility to radiation damage. As the demand will be low and extensive development efforts are needed, production of radiation-hardened chips lag behind the most recent development...

 VU2ESE has announced the launch of zBitx on the BITX group. It is available for purchase at http://www.hfsignals.com/ and delivery will start in February 2025. According to VU2ESE, it is a low cost 5 Watt, 80m to 10m QRP radio with a 480x320 touch screen that allows you to run CW, FT8 and other digital modes without needing even a phone that the original zBitx needed. As previously posted, zBitx is based on a Raspberry Pi Zero 2 W, which gives it the prefix 'z'. The physical size of zBitx is just 6 inches by 3.5 inches, 1.5 inches thick, weighing just 250gm, and includes a battery case that can hold two 18650 lithium polymer batteries. One has to get batteries from elsewhere. External DC supply can also be used with a maximum of 9V. zBitx seems to be quite 'pocket friendly' both in the literal sense and cost wise! An HDMI monitor, keyboard and mouse can be plugged in, to use like a QRP base station. zBitx runs the same software as sBitx radios. zBitx will ship with...

 LCR meter is an instrument used to measure inductance (L), capacitance (C) and resistance (R) as the name indicates. They can measure the impedance to a sinusoidal waveform of definite frequency and convert the measured value to capacitance or inductance. Higher end machines can measure true inductance or capacitance, equivalent series resistance of capacitors and Q factor of inductors. As actual capacitors and inductors are not ideal devices with only either capacitive or inductive components, they have a resistance in series which is defined as the equivalent series resistance. It is often taken as a resistance to alternating current, measured at a specified frequency which could be the self-resonant frequency or 100 kHz for switched mode power supply ( SMPS ) components and 120 Hz for linear power supply components. Q factor or quality factor is the ratio of a resonator's center frequency to its bandwidth when subject to an oscillating driving force. It is a dimensionless param...

Caution: VU2XTO has informed that high power with a linear amplifier should not be delivered to this loaded coil dipole as it can result in heating of coils.  I can hardly squeeze in a 40m inverted V at my home. Still I wanted to try out 80m as some of my VU friends have started trying it out. I was told by an online DX friend that 80m is a very busy band in EU with DX even up to Middle East at night. I was active on 80m in 1980s with a horizontal dipole antenna tied on top of coconut trees at my parents' home using a homebrew 3 x 807 AM/CW radio. VU2XTO design published in the Madras Amateur Radio Society Newsletter, Volume 26, Issue 2, July-September 2018 has the details of an 80m antenna for restricted spaces. What we need is a couple of 118 microhenry loading coils and about 14 m of insulated copper wire. For the 118 microhenry coils, VU2XTO has suggested a 15cm UPVC former of 1.5 inch diameter and 18 SWG enamelled copper wire wound closely for a span of 11cm. It is basically a...

 A guide is presented to help you build a functional ham radio station with a limited budget. You will learn how to choose the right equipment, build antennas, and set up your station for successful communication. In this era of multiple modern communication modalities, the thrill of ham radio is of communication without the internet and cellular network. Imagine that you are in remote areas without cell phone coverage, if you have a portable ham radio setup, you can still contact your friends around the world with similar setup. That is how ham radio or amateur radio has been deployed in natural calamities also, when the conventional communication networks are down. Unlike other hobbies, amateur radio needs a license in the country in which you are operating from. That is needed for multiple reasons including security concerns and need to avoid interference with other radio services. Radio amateurs are required to appear for an examination, generally involving electronics, rad...

The fascinating science of radio wave propagation is explored, demystifying how these invisible waves travel through the air and interact with antennas. We will explore the fundamental concepts behind radio wave propagation, offering a deeper understanding of how radio communication works. Radio waves are the invisible force behind our communications around the globe. Till recently, long distance communications across the globe depended on high frequency radio waves, of which the short waves were more important. They would go up from the radio transmitter and get reflected off the ionosphere, a special layer of the atmosphere which gets ionized by the sun rays. Now with the presence of numerous communication satellites, the role has been taken over by very high frequency, ultra high frequency and super high frequency which are known in short as VHF, UHF and SHF respectively. These waves do not get reflected by ionosphere, but go straight into space and hence need satellites to receive...

 Important specifications of an electret microphone are its directivity, sensitivity and signal to noise ratio. Directivity is the directionality or polar pattern and indicates how sensitive it is to sounds coming from different directions and angles. Omnidirectional microphones can pick up sound from any direction like an omnidirectional antenna. They are useful for picking up signals from a group of people. But this can also be a drawback as it can pick up ambient noise and unwanted sounds. Unidirectional microphones pick up sounds primarily from one direction and can eliminate background noises and unwanted sounds. Sensitivity of a microphone measures how well it picks up sound. A sensitive microphone can pick up even weaker sound signals and sounds from a distance. There is also a related parameter known as sensitivity reduction, which is the decrease in gain when the voltage of the power source for the electret microphone decreases. Electret microphones with built-in battery f...

A repeater is a combination of a receiver and a transmitter that receives signals and retransmits it so as to cover a longer distance. Usually repeaters are located at high elevations so that two stations located at lower elevations can communicate with each other through the repeater at longer distances. Most of the repeaters are for VHF and UHF frequencies , while there are some repeaters for 10m and and some for higher frequencies. In my region, all the repeaters are for VHF while there are a few UHF repeaters in other regions of the country. Usual communication on VHF, UHF and higher frequencies are limited by line-of-sight. Hence repeaters are needed for long distance communications on this frequencies. As an example, I am able to communicate easily through VU2MJJ repeater all the way from Kasaragod about 180 km North to Kottayam, which is about 200 km to the South. Without the repeater, maximum distance I can contact is usually about 20 km, though sometimes it might be possible t...

 Genetic antennas are also known as evolved antennas and they often resemble paper clips bent in different ways and connected to a radiofrequency connector. Unlike usual antennas which are most often designed by humans, now-a-days with the help of computer modeling as well, genetic antennas are designed by automatic computer design using an evolutionary algorithm that mimics Darwinian evolution. These algorithms have been called genetic algorithms. Studies on genetic antennas have been published as early as 1990s [1]. It was considered for mission-critical applications which involved stringent, conflicting or unusual design requirements like unusual radiation patterns, for which none of the existing antenna types were adequate. A 2014 paper described Two Novel Antenna Systems for Triband GNSS Applications [2]. GNSS stands for Global Navigation Satellite System and refers to any satellite constellation that provides global positioning, navigation and timing services. Some of the exa...

 Electrets are the electrostatic equivalents of permanent magnets. While a permanent magnet has two magnetically charged poles, an electret has two electrically charged ends. It has internal and external electric fields just like the magnet has magnetic fields. In short, electret is a dielectric material which has electrical polarisation. Electrets can be produced by heating a material and cooling in the presence of strong electric fields. They can also be manufactured by embedding excess negative charge in a dielectric using a particle accelerator. Alternate method is to embed charges on the surface using high voltage corona discharges. Embedded charges decay as a function of dielectric constant and resistivity. Material like polytetrafluoroethylene (PTFE) with extremely high resistivity can retain the charges for extremely long periods. Just as there are naturally occurring permanent magnets, quartz and and other forms of silicon dioxide can behave as natural electrets. An electr...

 Heard one friend mentioning on 40m that his new linear power supply has provision for 50 Volts needed for LDMOS. Saw a mention of LDMOS on the QRZ page of another ham as well. That prompted a readup on LDMOS as I was not familiar with it. LDMOS stands for Laterally Diffused Metal Oxide Semiconductor and is a type of MOSFET or Metal Oxide Semiconductor Field Effect Transistor. They are designed for high power and high frequency applications. That would explain why it is being used in amateur radio linear amplifiers. Lateral diffusion of the source and drain region enhances the transistor’s ability to handle higher voltages and power effectively. They have high power density, linearity, efficiency, high breakdown voltage and low on-resistance. On-resistance of a MOSFET, also known as the drain-source on-resistance, is the resistance between the drain and source of the MOSFET when it's in the on state. As already mentioned, they are useful in construction amateur radio linear am...

 Listened to the downlink frequency of the cross band repeater on International Space Station just now. It was an 80 degree maximum elevation visible pass in my region. I could hear my friends talking through the repeater very well. But somehow my calls did not reach them, may be because my homebrew Slim Jim antenna does not have enough gain to reach up to the Space Station on the uplink! Afterall it is not well tuned and the lowest SWR which I got was about 2:1. I need to try tuning it again to bring down the SWR to near 1:1 and then try again for similar high elevation passes. Yesterday evening I could hear the NA1SS beacon with a 31 degree maximum elevation pass. But there were no stations on the pass.

 Supercapacitors are also known as ultracapacitors. They are high value capacitors much above the usual electrolytic capacitors which we use in our hobby electronics projects. As an example, the linear power supply of my VHF radio has four 2000 microfarad capacitors. Supercapacitors have values in Farads, as can be seen in the image showing a supercapacitor of 4 Farad. For a record, 10,000 Farad graphene supercapacitor created by Sunvault Energy and Edison Power Company is considered the most powerful supercapacitor to date. Supercapacitors have high power density and fast energy discharge and recharge capabilities. Commercially available ones can have energy density of 5 Wh/kg (Watt-hour per kilogram) while experimental graphene based ones can have energy density as high as 28.5 Wh/kg. This can be compared with the much lower energy density of an aluminium electrolytic capacitor which is 0.01 to 0.3 Wh/kg. Though these energy densities are still lower compared to the 30 to 40 Wh/k...

 Sometime back we had discussed about diplexers used for LEO satellite operations and duplexers used for repeaters. Diplexer is meant for two different bands like VHF and UHF while duplexers are meant for two frequencies on the same band. Now what is an HF triplexer used for? HF triplexer is typically used to connect three radios to a single multi-band antenna as during field day operations. Advantage is that multiple radios can be operated by multiple operators without having to put up different antennas for each radio. Outputs of the three radios, operating 20, 15 and 10m bands can be combined into a single output by the HF triplexer and sent to a single triband antenna. The triband antenna should be a well tuned antenna with VSWR of 1.5:1 or lower on all bands. HF triplexer cannot be used on non-resonant antennas which need a tuner to operate. Additional protection for the receivers are needed to prevent overloading from the other transmitters connected to the HF triplexer. Ins...

  Raduino circuit board supplied with µBITX has an arduino soldered to the Raduino board, control lines for the display unit, Si5251a PLL clock generator chip, 5V regulator and a 16 pin connector to the µBITX main board. Arduino is the microcontroller which runs the BITX software defined radio. Connections are there to front and/or rear panel components like key jack, power supply connector and rotary encoder. Rotary encoder is an electromechanical device that converts the angular position or motion of a shaft to analog or digital output signals. Typical use of a rotary encoder is as the tuning control. Arduino nano can be programmed by connecting a USB cable from the computer to the USB mini-B port on the arduino nano. Firmware for the Raduino/Arduino control is available from the github page of VU2ESE . Other versions of firmware by different authors are also available online. If the Raduino is damaged by any reason, there are options to replace either the individual components ...

  Vivaldi antenna is a broadband antenna, also known as Vivaldi aerial and tapered slot antenna. Vivaldi antenna was invented by Peter Gibson in 1978. It can be made using a solid piece of sheet metal or printed circuit board. The illustration shows a Vivaldi antenna made from double sided printed circuit board material. A single Vivaldi antenna transmits linearly   polarized   electromagnetic waves. If two antennas placed orthogonally are fed 90 degree phase shifted signals they can generate circularly polarized electromagnetic waves similar to   cross Yagi   used in satellite communications. Vivaldi antennas are typically made on printed circuit boards cost effectively for microwave frequencies of 1 GHz and above. It has been mentioned that the antenna was named after Antonio Vivaldi a 17th century Italian composer, in the year of his 300th birth anniversary. You may note that the tapered slot of the Vivaldi antenna resembles a trumpet and Vivaldi had written ...

 It is common knowledge among radio amateurs that a 40m center-fed half wave dipole antenna will work very well on 15m. That is because center fed dipole antennas, whether it be a horizontal dipole or an inverted V, will resonate on all odd harmonics. Amateur band allocations are mostly as harmonics, for example, if you consider 3.5 MHz 80m band as a fundamental frequency, 7 MHz 40m band is its second harmonic, 14 MHz 20m fourth harmonic, 21 MHz 15 m band sixth harmonic, 28 MHz 10m band is 8th harmonic. This used to help in the days of homebrewed radios when the harmonics of a fundamental frequency oscillator could be amplified using corresponding tuned circuits to get on higher bands. When crystals are used for the fundamental frequency, stability is also good, though it restricts operation to a single frequency. In case of antennas, as already mentioned, center-fed half wave dipole antennas resonate on odd multiples of fundamental frequency while end fed half wave dipole antenna ...