Johnson's Techworld

 Last year I had seen many of my local ham friends posting on social media on Europa Clipper 'Message in a Bottle Campaign'. Never thought that it has reached great heights until I saw the participation map on NASA's website today! A glance at the map will tell you that the maximum number of participants in the  'Message in a Bottle Campaign' was from India after the United States of America. Now it is too late for anyone to participate as the deadline is over. There was an opportunity to have your name engraved on NASA's Europa Clipper spacecraft as it travels 1.8 billion miles to explore Europa, a moon of the largest planet in our solar system, Jupiter. Scientific evidence suggests that beneath the icy crust of Europa, there is a large ocean, bigger in size than the combined size of all oceans on Earth. That is why Europa Clipper mission is going in search of life on the satellite of Jupiter. NASA's Europa Clipper is scheduled for a launch on October 10, 2...

 I came to know that a CubeSat ULOG3  was being launched on a helium balloon today morning. VU3KVB from Chennai was the amateur radio co-ordinator of the event and I was in touch him over phone from early morning. Though the launch was scheduled for 6 am, there was a delay of about one hour for the launch. After the launch VU3KVB informed me that he was able to hear the signals 5,9 on handheld radio with rubber duck antenna, even when the CubeSat was 30 km from his location.  I was told that it had a 500 mW transmitter for sending SSTV images containing photographs taken by the CubeSat, overlaid with GPS data which would include longitude, latitude and speed of motion. Barometric data will also be provided by the barometric sensor. It had an 8000 mAH battery and was expected to reach an altitude of 32 km, being filled with about 800 gm helium. When the balloon bursts at high altitude, a parachute would be deployed and as per wind prediction, it would land somewhere in Dha...

 Darlington pair is a pair of bipolar junction transistors connected in such a way that the emitter of one transistor is connected to the base of the other. The current amplified by the first transistor is amplified further by the second transistor. Collectors of both transistors are connected together. The Darlington pair has a higher current gain than each transistor taken separately. Combination of two transistors connected together in a single package is also available. Alternatively two transistors can be connected in the Darlington configuration to get a Darlington pair. The first transistor can be of low power type, but the second one needs to have higher power rating. The configuration was invented by Sidney Darlington in 1953. The maximum rated collector current of the Darlington pair is that of the second transistor. One such integrated device is 2N6282, which has current gain ( hFE ) of 2400 at a collector current of 10 A. A disadvantage of the Darlington pair is doublin...

 The amateur radio satellites which I have operated so far have uplink and downlink in the VHF and UHF bands. Some of my friends also operate on the Qatar Oscar 100 Geostationary Amateur Radio Satellite which has a uplink on 2.4 GHz band and downlink on 10 GHz band. It was only today that I came across a post by ZL2BJO on the AMSAT bulletin board mentioning about the 10 GHz downlink of CatSat . As usual, that prompted a read around and soon I came to the webpage of The University of Arizona mentioning about HAM Radio Community and CatSat. It has been mentioned that in addition to the 10 GHz primary science patch antenna and radio, CatSat has a 5 GHz patch antenna that will enable the spacecraft to operate for limited periods of time as a linear transponder. It will be possible for radio amateurs based on Earth to communicate through the transponder when it is enabled. CatSat is a 6U Cubesat measuring 30 x 20 x 10 cm launched on 3rd July 2024 by  Firefly Aeros...

  Small magnetic loop antennas can be used both indoors and outdoors. They are cheap, easy to build antennas which have been used for even DX contacts with an indoor antenna running 50 watts for CW, PSK, JT65 and FT8 modes on 10 to 40 meters according to K5IJB! Wide spaced variable tuning capacitors which prevent arcing are needed when planning for higher power. You may be aware that the spacing in question is between rotor to stator elements and not between stator elements and there are formulas for calculation of the minimum spacing required for a given voltage. Small loop antennas are small in comparison to the full wavelength of the transmitting frequency. But they are much larger than the small receive only loop antennas which you may have seen supplied along with broadcast receiving sets. In its simplest form a magnetic loop antenna is a loop of wire with an RF current flowing through it. RF magnetic field generated by the current gives electromagnetic radiation, just like a...

 Alpha, beta and gamma in case of transistors indicate the current gain in different configurations. Alpha is the current gain in common base configuration. It is the ratio of collector current to emitter current. Alpha is always less than 1. In common base configuration, emitter is the input terminal and collector the output terminal while base is the common terminal. This configuration is also known as grounded base configuration. When there is no AC input, the alpha is known as DC Alpha. Alpha can be increased by making the base thin and lightly doped.  Beta is the current gain in common emitter circuit. It is the ratio of collector current to base current. Beta is always more than 1. This configuration is also called grounded emitter configuration. Base is the input terminal and collector the output terminal. Gamma is the current gain in common collector circuit. Base is the input terminal in this configuration, also known as grounded collector configuration. Here output t...

  NanoVNA is a handheld Vector Network Analyzer useful for measuring and analyzing radiofrequency circuits. NanoVNA works by sending a test signal through the circuit and measuring the reflection and transmission of that signal. It can measure the impedance and frequency response. Thus NanoVNA is useful for testing antennas, tuning filters, and measuring cable loss. Though it may not be as accurate as more expensive lab equipment, it is a useful tool for the Radio Amateur. Vector network analysis involves measuring the amplitude and phase of a test signal as it travels through a circuit. Input and output signals are compared to determine how the circuit is affecting the signal and calculate its characteristics. NanoVNA was developed in 2018 and the open-source nature has made it popular among hobbyists. While the initial version of NanoVNA was powered by a USB source, revised versions can be run on 3.7V Lithium ion battery. Different versions with varying frequency range are availa...

 TSOP1738 Infrared Receiver is in an integrated chip with three terminals outside, one for ground, another for power supply and the third for signal output. It works on 38 kHz. There are other ICs in the series which work on other frequencies like TSOP1730  which works on 30 kHz and TSOP1736 which works on 36 kHz. The 38 kHz working frequency of TSOP1738 is not the frequency of the infrared light which it senses, which is very much higher than 38 kHz. It is the carrier frequency which is modulated by the infrared signals in the infrared remote. The output from TSOP1738 can be fed to a decoder to achieve the actual function of the remote control. In the various devices which use at home like television and air-conditioner use remote controls to operate them. In this simple experiment , output of TSOP1738 sensor is being fed to a green LED through a 1K resistor. The LED will blink if you point any remote control working on 38 kHz is pointed at the IR sensor and pressed. TS1730 h...

 Resistors are passive elements in electronic circuits meaning that they do not need a power supply unlike active devices which need a power supply for them to function. Other common passive elements used in electronic circuits are capacitors and inductors. Resistance of a resistor is expressed in Ohms. Higher values may be expressed as Kilo Ohms or Mega Ohms. Kilo Ohms meaning 1000 Ohms and Mega Ohms meaning million ohms. Resistors come in different wattages depending on their size, indicating heat dissipation capacity. The resistors shown here are quarter Watt resistors while half Watt and one Watt resistors are also available. Higher and smaller denominations are also used in specific applications depending on the circuit demand. The value of the resistor is indicated on the resistor with a colour code. The resistors shown here have a four band colour code, which is the most common one in use. First two bands indicate the resistance value which has to be multiplied by the code o...

 As you can see in the picture, open parallel wire transmission line is often called a ladder line. It has two bare wires held at exactly the same distance apart by insulating spacers which could be made of plastic. One of my local friends used pieces of drip irrigation tubings as spacers as they were UV protected! Advantage of ladder line is that by using a minimum amount of dielectric insulating material, attenuation or power loss per meter is less less than the usual coaxial cable. As a comparison, if the loss in coax is 2 dB, corresponding loss in a ladder line may be just 0.2 dB. If insulated wire is used, relative permeability of the insulation will alter the characteristic impedance of the ladder line. Other factors which affect the characteristic impedance are the ratio of the wire spacing to wire diameter and conductive loss in the rung insulators. Typical impedance though taken as 450 Ohms, could vary and may even be 600 Ohms, requiring an external antenna tuner for match...

 There was a pass of International Space Station with about 37 degree maximum elevation in my region. I did not expect anyone as it is a noon pass on a working day. Towards the time of closest approach in my region, I could clearly hear my signal on the downlink. So I was sure that the transponder was active. I continued listening and to my pleasant surprise, I could hear VU3DTT calling a few times, near the end of pass in my region. I went outside and turned the antenna further Northward to get the signals better. I could hear him two more times as well as the ARISS beacon announcing NA1SS. Though I did try calling back a few times, presumably my calls did not reach him. The satellite was far away by that time for my limited setup of fixed Moxon Yagi with a single Moxon on VHF to reach up to the Space Station! Here is the curated recording of the pass, after removing the silent periods.

 Yesterday, when I read about NPN transistor BC547B and the corresponding PNP transistor BC557B, I noted that the former had a typical transition frequency ( f T ) of 300 MHz and the latter had a typical transition frequency of 150 MHz. Now what is this transition frequency? In simple terms, it can be considered as the frequency at which the amplifier gain becomes unity. That is the highest frequency below which the transistor can function as an amplifier. It indirectly reflects the total time current carriers (electrons or holes) take to travel from the emitter to the collector. In actual circuits, the effective higher end operating frequency will be only a fraction of the transition frequency as parasitic capacitances lower the maximum frequency at which it can operate.  Radio amateurs planning to design radio frequency circuits will be interested in transistors with higher transition frequency which we often call as RF transistors, in comparison to AF transistors for audio ...

 An important parameter in a transistor is hFE, which represents the current gain of a bipolar junction transistor. Bipolar junction transistors have a collector, base and emitter. hFE is also known as the β of the transistor. hFE stands for H ybrid parameter F orward current gain, common E mitter. It is measured by dividing the collector current by the base current in a common emitter configuration and measures the amplification of the transistor. When a diode is forward biased, meaning that the positive pole of the battery is connected to the anode of the diode, there is a small drop in the potential across the diode, typically 0.7 V in a silicon diode. In rectifier diodes, cathode is marked as a ring or stripe on the body near the cathode pin or lead. When the diode is reverse biased, no current flows across it, as when the anode is connected to the negative terminal of the battery.

 I was quite happy to read the email from Félix EA4GQS, AMSAT EA, on the AMSAT bulletin board just now. He has mentioned that new HADES-R and HADES-ICM satellites will be available to amateur radio satellite operators in early 2025! After the decay of TEVEL series and expected decay of SO-121, we are facing an acute shortage of FM amateur radio satellites. Though I have not been able to have a QSO on SO-121 yet, these new satellites are expected to have a higher power transponder of 250 mW compared to 40 mW of SO-121. So I am quite hopeful of working at least high elevation passes of the new satellites. Both new satellites are 1.5p PocketQubes. As I had mentioned earlier, one PocketQube unit is 5 x 5 x 5 cm, compared to the 10 x 10 x 10 cm of a CubeSat unit. The satellites are expected to be launched on SpaceX Transporter-12 and 13 missions respectively. In addition to the FM repeater, they will have digital communication modes and telemetry. FM repeater will be available...

 Secure Argentinian Amsat Satellite Pass Prediction Page informed by Pedro  LU7ABF is: https://mail.amsat.org.ar/pass.htm

In the remote past I have had several instances of antennas coming down in the rainy season, which is also the windy season. Though the first part of the raining season here is almost going away, the next set is due soon. My nylon ties would have borne the brunt of solar ultraviolet rays in the summer and are likely to break off in the winds. So I thought of giving extra reinforcement with 2.5 sq mm insulated copper wire, which I had in surplus after my HF antenna projects. The masts are all made of non-conducting material, some of CPVC, others of PVC and fibreglass. Hope I will not have any fallen antennas in this season, though it will be an ongoing process of regular inspection and fortification.

 I connected a step down transformer to the input of an amplispeaker with a 50K cermet preset potentiometer to listen to the 50 Hz hum of alternating current. The intensity of hum increased gradually when the resistance value of the preset was reduced to half gradually. Of course, I did not attempt reducing it fully for fear of blowing out the input circuit of the amplifier with over 10 V in the output of the step down transformer. I used the same method to check for any hum in the filtered output of the bridge rectifier which I made the other day. I could not hear only a minimal hum. It was a crude method of checking the output waveform short of an oscilloscope!

 Three pins of the cermet 50K preset potentiometer were placed on three rows on a solderless breadboard. Jumper wires were used to connect the terminals to a digital multimeter. 200K range of resistance was selected in the multimeter. To start with, total resistance across the two terminals on one side of the cermet potentiometer was measured and found to be 50.7K. Then the resistance between one of those terminals and the central terminal was measured. Change in resistance as the central screw of the preset potentiometer was rotated to either side was recorded.

 Preset potentiometers are are variable resistors. The resistance value can be varied using a screwdriver to turn the screw mechanism on the device. Cermet is a combination of ceramic and metal used in several applications including the manufacture of resistors, especially potentiometers. Metal provides ability to undergo plastic deformation while ceramic provides hardness and high temperature resistance. Metallic elements usually used in cermet are nickel, molybdenum, and cobalt. Marking 50 3 indicates a resistance value of 50 Kilo Ohms. Number three meaning 10 to the power of 3.

 Today I checked the input to the bridge rectifier from the step down transformer and the output of the bridge rectifier. As expected, there was a significant difference between the two. AC input to the bridge rectifier is measured as RMS voltage and the rectified DC voltage output is expected to be be 1.414 times the AC input (root 2 times). The measurement was conducted at no load condition. When a load draws current from the bridge rectifier, there will be some fall in the voltage as no voltage rectifier circuit has been included in the demo bridge rectifier circuit. Even otherwise there will be voltage fluctuation according to fluctuation in line voltage.

 Speaker driver is what you see inside a loudspeaker enclosure as the active part which produces the sound according to the signals from the audio output of the amplifier. Tweeters cater to high frequency while woofers and subwoofers cater to lower frequency. Mid-range drivers reproduce the frequencies in between. A loudspeaker enclosure usually has all the three types inside. Below a woofer there will be a port known as bass reflex port, for enhancing the performance of the woofer.  Outer part of the electrodynamic speaker driver is the chassis or frame, also known as the basket. Paper like cone fixed to it produces sound by its vibration. Voice coil inside a cylindrical permanent magnet, suspended on a 'spider' produces the linear movements of the cone for producing the sound according to the signal received from the amplifier. A dust cap prevents entry of dust, specifically ferromagnetic material, into the voice coil assembly inside the cylindrical magnet. Each driver unit ...

 Displaying the different selections of measurements available on a digital multimeter. A couple of screws on the reverse side can be removed to see the inner structure as well as to replace the 9V battery when needed. For alternating current there are only two ranges of measurement, 750V and 200V. Several ranges are there for DC voltage and current as well as resistance. 10A range needs a switch of the leads to a different port. Separate port is available for testing NPN and PNP transistors.

 There are several types of audio connectors. Most commonly used one these days is the 3.5 mm TRS connectors (Tip, Ring, Sleeve), which are stereo pins. Corresponding mono pin will be called as TS pin as it has only tip and sleeve connections and no ring. RCA connector was from Radio Corporation of America. 6.35 mm pins are used in microphones with cords. Base of the microphone has an XLR pin, which is connected to an XLR socket on the cable. Other end of the cable has a 6.35 mm TS pin. Adaptors are there for converting 3.5 mm to 6.35 mm and vice versa, depending on the need.

 Checking SWR using a patch cable to connect the SWR meter between the radio and the antenna was discussed earlier. Most of the modern SWR meters are cross needle SWR meters which will show both forward and reflected power with two movements simultaneously along with SWR on another scale. In the SWR meter illustrated here forward power is indicated by the black scale and reflected power by the blue scale. Multiplier for the power can be x1, x10 or x100 depending on the position of the selector which is not shown here. SWR is indicated by the crossing point of the two movements by the red scale.

 I used four rectifier diodes and a 1000 MFD filter capacitor to assemble a simple bridge rectifier on a breadboard. Used jumper wires of red and black colour to take the output of the power supply. As the step down transformer from 230V to 12V was a bit heavy, it was kept separately. This will constitute a linear power supply in which the mains voltage is directly stepped down to the output level. In SMPS or Switch Mode Power Supply, a radiofrequency waveform is generated first so that step down transformer can be much smaller at higher frequency. Switch Mode Power Supplies will be much lighter as the RF transformer size is small. But SMPS may have radio frequency interference when used near to amateur radio receivers. RFI suppression circuits will have to be included for this. In case of linear power supply, the transformer uses a laminated core to reduce eddy currents and power loss as heat. Eddy currents will reduce the already lower efficiency of linear power supplies.

 If you look at satellite information page at N2YO.COM, there are a couple of lines named as Two Line Element Set (TLE) near the bottom of the page. These are also known as Keplerian elements or Keps in short. They can be used in satellite tracking softwares like Gpredict . Once TLE is added to the software, it gives information on possible passes in your region as well as Doppler correction needed during the pass. After the line number in each row, there is the NORAD ID of the satellite, which is 25544 for International Space Station.  NORAD stands for North American Aerospace Defense Command. Orbital positions of satellite can be calculated from TLE using mathematical models which predict the effect of perturbations caused by Earth's shape, atmospheric drag, radiation and gravitation effects from other heavenly bodies like the Sun and Moon. The mathematical model for near Earth objects with an orbital period of less than 225 minutes is known as Simplified General P...

 Solderless breadboard is a convenient way of testing out prototype electronic circuits. It is also a good educational tool. There are sets of 5 clips within the holes on either side of the central notch. They are the active terminals used for mounting electronic components. Each set in a row are connected to each other. The columns on the left side of the notch are named A, B, C, D, E and those to the right side are named F, G, H, I, J. These are the terminal strips. The notch provides for air circulation and cooling when Dual-in-line pin Package Integrated Circuits (DIP IC) are inserted in such a way that one set of pins go into column E and the other set goes into column F. In a full sized breadboard, the rows are numbered 1 to 65. Breadboards can be connected to each other to form a larger breadboard using the dovetail connectors on the side. The columns on either side of the named ones are the bus strips to provide power supply. One of these can serve as the ground terminal. T...

 Listened to a pass of International Space Station at 0730z in my region. It was a low elevation pass with only 16 degrees maximum elevation. I could work VU3YFD with my limited setup and hear VU2AAP. Though I gave a few calls to VU2AAP, I could not hear any reply. Meanwhile in my commentary, I had mentioned that an https site for Argentinian Amsat Satellite Pass Prediction page is available at https://mail.amsat.org.ar/pass.htm , Courtesy: Pedro LU7ABF. Antivirus software and Windows 11 usually prevents access to the old http site at: http://amsat.org.ar/pass.htm. So this new site will be useful for those who shy away from using this very useful webpage because of security warnings. 

 GreenCube also known as Italy Oscar 117 (IO-117) was very popular among amateur radio satellite operators as it could provide much longer distance communications than the Low Earth Orbit satellites. That was because GreenCube was a MEO or Medium Earth Orbit satellite located at about 5000 km altitude compared to the about 400 km altitude of International Space Station. Being at a higher location, GreenCube had a higher footprint and I am aware of hams from my region contacting stations in United States of America, which is impossible with Low Earth Orbit satellites. GreenCube had a digipeater which needed specialized setup compared to the usual FM satellites which I work. Moreover, the higher altitude mandated the use of more sensitive antennas and preamplifiers. A news item posted on AMSAT bulletin board mentioned that GreenCube satellite developed by S5LAB has likely ceased functioning due to radiation damage. Of course, the GreenCube mission was highly successful as it had exce...

 Long back when I used to assemble hobby electronic projects, components were mounted on printed circuit boards through holes in the circuit board on the side opposite to which the circuit was printed. The leads of the devices would be soldered to the PCB for good electrical contact. Another method used was mounting on a breadboard, which as a temporary method used mainly for experimenting with prototypes. In surface mount technology, components are mounted directly on the printed circuit board, and not through holes on the opposite side. SMT allows for better manufacturing automation, reduces cost and improves quality. More components can be fitted into a given area. SMD have smaller leads, short pins or flat contacts. When needed, both technologies may be implemented on the same PCB when components not suitable for SMT like large transformers and power semiconductors with heat sink have to be installed.

 Light Dependent Resistors (LDR) or Photoresistors are widely used in automatic street lights and garden lights. Ambient light falling on the device triggers an electronic circuit which switches off the lights. When light falls on the LDR, the resistance falls from a few mega ohms to a few hundred ohms. Lead sulphide and Indium antimonide are two important substances used in the manufacture of LDRs. LDR is a passive device and does not have a PN junction as in active devices like photodiodes and phototransistors. There is a lag between the change in illumination and change in resistance which makes LDR not suitable for fast switching purposes.

 Tropospheric Scatter Propagation is known in short as Troposcatter Propagation. Troposphere is the lowest layer of the atmosphere. Though Troposcatter is typical at microwave or super high frequency or SHF band , it can also occur at VHF and UHF bands. The height of the troposphere is about 20 km near the equator, which comes to about 9 km in polar regions in summer. Height of the troposphere is more in summer than in winter. Troposphere can refract higher end of the radio spectrum. HF is reflected typically by the ionosphere, much above the troposphere. Tropospheric scatter was used mainly by the military prior to the era of satellites. When the transmitting and receiving stations point their antennas to a common scatter volume in the troposphere as shown in the illustration, troposphere refracts the signal towards the receiving station. Troposcatter may work from frequencies as low as 144 MHz to 10 GHz and useful communication can occur from 100 km to 700 km. Typically the trans...

 Transequatorial VHF propagation was first noted by radio amateurs in August 1947 when Mexican stations could work Argentine stations regularly across the equator in the late afternoon and early evening on 50 MHz. This occurred for few more years during the maximum of Solar Cycle 18. Transequatorial Propagation came down during the period of sunspot minimum and reappeared in 1955 and continued through the maximum years of Solar Cycle 19. We can expect similar conditions as we are heading for the maximum of Solar Cycle 25 in 2025. Two types of transequatorial propagation has been described. One occurring during late afternoon and early evening with maximum distance of about 6000 km in low VHF band of 6 m. Second one was between 7 pm to 11 pm local time with contacts on 2 m and sometimes on 70 cm band. Mechanism by which transequatorial propagation occurs is the presence of equatorial anomaly, which is a high concentration of electrons on either side of the equator in the region of 1...

 Semiconductor rectifier diodes are PN junctions with P type semiconductor for anode and N type semiconductor for cathode. They are used to convert alternating current to direct current and is widely used in various electronic devices. Simplest form is a half wave rectifier which uses only a single diode and the output has only half of the alternating current as output. It is a pulsating DC at the frequency of the input AC waveform. Full wave rectifier uses a couple of diodes fed out of phase using a centre tapped transformer so that both halves of the AC waveform appears in the output as a pulsating DC with twice the frequency of the supply voltage. Bridge rectifier uses four diodes and a transformer without a central tap. The output waveform is just like that of the full wave rectifier with two diodes. As both these are DC with ripples, smoothening out of the waveform can be done by using a high value capacitor across the output. Further smoothening out can be done using an induc...

 When I started off in amateur radio in 1985, Solar Cycle 21 was nearing its end with sunspot activity going down. Solar Cycle 22 started in September 1986. So I had the opportunity to witness propagation on 40m band going down and that on 80m becoming better. In those days, I had no option for higher bands as my Philips Prestige home radio which I used for RX did not cover them. I was unaware of regional activity on 160m and I do not remember whether my radio had covered that band. I still remember the EC Net also known as East Coast Net on 80m at 10 pm, to which I used to check in, mostly on CW as my homebrew radio, 3 x 807 vacuum tube radio, was not that great on AM for 80m. Now we are in Solar Cycle 25, which started in December 2019 and we are headed for the maximum sunspot activity soon. When we pass that maximum, we will see higher bands going down and lower bands picking up. In the beginning of 2024, my favourite DX band was 10m, due to high sunspot activity. As we go ...

 Phased array antennas are those in which the radiation pattern of the antenna can be changed without physically moving the antenna. For the ham radio operator, it would be quite interesting if you can steer the beam without the need for an antenna rotator! The same principle is used in ultrasound imaging to steer the ultrasound beam. If several antenna elements are fed from the same transmitter with a phase shift, the direction of the beam can be changed by changing the phase shift. This is possible when a computer controls the phase shift to each element. It is widely used in the field of radar imaging. In the illustration, computer controlled phase shifter changes the phase of the signal fed to each element. The progressive delay in signals would in effect change the direction of the superimposed signal wavefront to an angle depending on the phase shift given. By altering the phase shift, the angle theta at which the beam is radiated, can be changed without physically rotating t...

  VU2SV Memorial Net on 7090 kHz with VU2NSL and VU3LLL as net controls. Plenty of signals on 40m waterfall display. Excellent band condition here today morning.

 Fractal antenna was initially presented by W1YW at the ARRL convention in October 1994. Fractal antenna uses a self similar design to maximize the effective length of the material used to receive or transmit electromagnetic radiation within a given total surface area or volume. Self similar design can be better understood by having a look at the public domain image from Wikipedia by Nathan Cohen (W1YW) which is shown below: The specialty of design is that fractal antennas are very compact and capable of multiband operations. Hence fractal antennas are useful in cellular telephony and microwave communications. Another advantage is that size is smaller without the use of additional component like a loading coil, which is often used to electrically shorten antennas.  Loading coils though they make antenna size more convenient for mounting, causes loss of RF energy in the resistance of the coils which is not zero! In a way the design can be considered similar to the linear l...

Ionosphere is a layer of the atmosphere which gets ionised, mostly during day time, due to the effect of sun rays and it is situated high above the atmosphere, almost the thermosphere. It may extend into the exosphere above and mesosphere below. When radio waves reaching the ionosphere has a critical frequency, above which it will just radiate out into the space. That is why VHF and UHF radiate straight to the space. But HF, below that critical frequency, will be reflected back to the earth, and to the ground, which will skip around the earth, and produce long distance communication. These are the layers of the atmosphere. The lowermost is the troposphere. That is the place where we are all walking about, lowermost layer of the atmosphere. Then comes the stratosphere. Beyond the stratosphere, you have the mesosphere, still beyond is the thermosphere and outermost layer is the exosphere. As you go up from the earth, due to the reduced effect of gravity, the atmosphere becomes thinner. S...

 My single band VHF only CP22E antenna has a phasing coil between the upper and lower elements. CP22E is a two-element 5/8λ stacked ground plane antenna with three radials. Upper and lower sections are assembled with the phase coil in between. Coil ensures that the phase of the waveform is same all along the antenna length so that both sections work together. This increases the efficiency of the antenna. Without a phasing coil an antenna with double the length will not work on the design frequency. As a simple example, 20m long center fed dipole antenna meant for 7MHz will not work for 14MHz, being an even harmonic, though it will work for 21MHz being an odd harmonic. In the same way, my CP22E VHF antenna works fairly well on the UHF amateur radio band as it is roughly the third harmonic. Dipole antennas can be made physically shorter than the usual half-wave dipole antenna by adding loading coils. It is useful for single band operation with narrow bandwidth. Of course it is a tra...

 USB printer cable has a type B plug at one end and a type A plug at the other end. Type B plug goes into the type B socket on the printer, while type A plug goes into the type A socket on the computer. Same cable can be used for Computer Aided Transceiver control (CAT control) in amateur radios like FT-710. The type B plug goes into the type B socket on the rear side of FT-710 and the type A plug goes into the computer for connecting it with the radio. This is useful in working digital modes and for automatic logging software in amateur radio.

 Wireless router range extender can be used at home when there is no good connectivity from the home internet wireless router to all the rooms. This router has 2.4 and 5 GHz WiFi channels. There are a couple of antennas, the polarization of which can be changed from vertical to horizontal and anything in between. Signal LED lights up in blue colour when good signal is being received from the router. If not, it becomes red. There is also an RJ 45 LAN port on the lower side of the range extender, which can be used to connect to the internet router through a local area network cable. Then the range extender can be programmed as a WiFi hotspot from which other devices can connect to the internet provided by the internet router. This is useful if you can wire a LAN cable from ground floor where the router is kept and the first floor or higher floors where the range extender is to be used. Mode change can be done using a linked app installed in a mobile phone.

 Light emitting diodes or LEDs produce light when electrons combine with holes in the semiconductor, releasing energy as photon. First ones to be produced were infrared and red LEDs. Other colour and white LEDs were invented later. Initial LEDs were of low power and later high power ones were invented. 7 segment LED displays will be familiar to most of you. Now there are LED TVs and large displays. OLED has an organic compound which produces light and is used in televisions. Three colour LEDs are RGB LEDs which have four leads instead of the two in usual LEDs. The longest of the leads is the common one. In usual LEDs, longer lead is positive. There are also blinking LEDs. Surface mount type of LEDs are used in LED lights which are fast replacing incandescent lights and fluorescent lights. LEDs work on low voltage DC and need a driver unit in LED bulbs, which are usually a small switch mode power supply, which can cause radio frequency interference in amateur radio bands, especially...

 Many of you would have noticed that some of the modern cars have a 'shark fin' antenna, quite different from the whip antenna seen on older cars for radio reception. They are quite sleek and have a better visual appeal than the older whip antennas. Aerodynamic design reduces atmospheric drag and makes it more durable and resistant to weather conditions. Accidental damage as when the car is quickly pulled into an automatic car wash is also unlikely. Beyond the usual function of radio reception, shark fin antennas can have other functions like navigation and tracking using global positioning system (GPS), WiFi data transfer, receiving cell phone and satellite radio signals and even internet signals, depending on the hardware connected to it. Some models have an option to connect an external whip antenna with an SMA connector .

 Capacitors were also called as condensers earlier. Even now, capacitor mics are known as condenser mics! The ones which I am showing are electrolytic capacitors with a polarity. Other varieties likes paper, ceramic and air capacitors have no polarity. Air capacitors are used as tuning capacitors. Tuning capacitors for higher voltage needs more spacing between the metal elements to prevent arcing.

  Happy to work 9W8ZZK from Borneo Island (3964.8 km) on 21.285 MHz SSB. He was coming here quite strong and I wondered why - He is on 50 W only, but with 7 element full size tribander Yagi! So that is the power of the antenna! I was on 100W, but my antenna was just an inverted V dipole for 40m, working on 15m as third harmonic.

  HCF 4017 is a 16-lead dual in-line package monolithic integrated circuit. It is a decadic counter with ten outputs. It can be used in circuits like LED chaser and frequency divider.

 First Contact on the 'Rare Bird' UVSQ-SAT, with VU2TEK! The satellite was at 600 km distance and elevation was 30 degrees, when I heard VU2TEK during the pass starting from 10:17 pm IST (UTC+5.30) on 14 September 2024. I had not luck during the contact on the morning of 14 September 2024, though VU2TEK could hear some station partly. That was a pass with maximum elevation 23 degrees here while the successful pass had 45 degrees maximum elevation. I continued hearing VU2TEK for a few minutes after our contact as well. As the satellite has been activated for 48 hours from 0000z on 14 September 2024, there will be two more passes in this region on 15 September 2024. But they are of lower elevation, 15 degrees and 13 degrees. 

 Today evening by about 5.30 pm local time, I could see several signals on the waterfall on 40m, which was quite unusual. In the morning hours 40m band is busy with several local nets and ragchews. But we have only one net in the evening, the Silicon City Net, that too will be over before 5.30 pm. Hardly one or two signals may be seen on the waterfall by that time on 40m. Today most of the stations on 40m were DX, possibly from Indonesia. There should have been some contest out there. I could hear several YL operators as well.  Checked 20m, which is usually active at that time with several long distance VU stations. It was the same today also, with dense signals on the waterfall on 20m, some even 5,9+20 dB. Moved on to 15m, which also showed a few signals on the waterfall. Seemed like Indonesian stations operating contests. There were YL operators there as well. With all the lower bands wide open, I was hopeful that 10m also will be open and give me a few DX contacts. But cont...

 UVSQ-SAT is activated only rarely. That is why I have called it as a 'Rare Bird'! Now it has been activated for 48 hours starting from 0000z on 14 September 2024. AMSAT Live OSCAR Satellite Status Page has shown a few reports of the satellite being heard. The satellite is at a low elevation of 365 km, below the orbit of International Space Station. There are four passes in this region during the 48 hours of activation. Now one in this region seemed to have heard it yet.

 UVSQ-SAT is a CubeSat which was launched on 24th January 2021. Though it was initially mentioned that UVSQ-SAT team will provide an availability of the transponder up to 20% of time for Ham Radio operations, that never happened and activations for Ham Radio were quite rare and unpredictable. Now the UVSQ-SAT team has announced on X that the transponder will be activated for 48 hours from Saturday September 14 (UTC 00h00). Uplink is on 145.905 MHz and Downlink on 437.020 MHz. No tone is needed for access. That is a welcome event when we are facing scarcity of FM satellites after the TEVEL series re-entered the Earth's atmosphere. Let us see if we can have a few contacts through the transponder. There seems to be couple of passes tomorrow and the day after in my region.

 HRC fuses are High Rupturing Capacity fuses. Older types of fuses used a simple wire which would melt and even burn off when a certain level of current is exceeded. That is how we used to have blown fuses in the yester years. The body catridge of HRC fuse is made of heat resistant material like ceramic and there are two metallic end caps which connect to the circuit in the fuse holder. The current carrying element within the fuse is made of silver and the internal space of the fuse body is filled with a powder which prevents overheating and allows the fuse to carry normal rated current. Beyond the rated current, the silver element vaporizes and breaks the circuit. Chemical reaction between silver and the filling powder produces a high-resistance substance which helps to quench the arc in the fuse.   

 This CW paddle was bought from a local ham. It works fine, but I have been a bit lazy to try it out! In this video clip I am demonstrating how to use it for practising Morse Code using the built-in keyer in my FT-710 radio. The same procedure can be used to send CW on air if you enable break-in using the function menu of the radio. While using the keyer for Morse Code practice, break-in should be switched OFF to prevent signals being transmitted.

 Many amateur radio satellite operators are also keen observers of weather satellite data. They regularly post images captured from weather satellite downlinks on various social media. Being in the tropics and going through rainy season currently, I thought of looking at the definitions of some tropical weather events. It may be noted that tropical weather events can occur even beyond the tropics as they spread to higher latitudes before they make landfall. Now what is a landfall? Most of the weather events originate in the sea and the intersection of the centre of a tropical cyclone with a coastline is known as landfall. But the strongest winds may not be exactly at the center. So it is possible get strong winds even before landfall. On the other hand, strongest winds can also be over the water at landfall. Tropical cyclones originate over tropical or subtropical waters with organized deep convection and a closed surface wind circulation about a well-defined center. Once formed, t...

 Well, I heard of a Quagi Antenna only yesterday, from VU2YE, a veteran LEO satellite operator in this region. He used to do even Moon Bounce with a long Quagi Antenna. Most of you would have heard of Yagi antennas or Yagi-Uda antennas and some of you would have heard of Quad or Cubical Quad antennas. Quagi antenna is one which combines the best aspects of both Quad and Yagi antennas. Typically a Quagi antenna has Quad driven element and reflector and Yagi director elements. Quad driven element is meant to take away the inherent disadvantages of a dipole. Gamma match can become less effective at VHF and UHF frequencies and I have found making and tuning a Gamma match for my VHF and UHF antennas quite cumbersome. Quagi is directly fed with 50 Ohms coaxial cable like RG-8/U as the impedance is around 60 Ohms at resonance. Quad loops can give a little extra gain than dipole driven elements as well. A two element quad may have 1.5 dB extra gain, but this does not increase much as the...

 As soon as radio amateurs establish contact over the radio, they exchange signal reports, typically in the R-S-T format. R-S-T stands for Readability, Strength and Tone, though the last one is meant only for CW signals. The system was developed by Arthur W. Braaten, W2BSR in 1934 and is continuing till date. Readability reports can spread from 1 for an unreadable signal to 5 for a perfectly readable signal. Very often radio amateurs are quite lenient and give readability 5 even if there is great difficulty in copying. Only rarely have I heard people giving a readability report of 4 and hardly do I hear anyone giving reports below that. Coming to signal strength, the range is from 1 for faint barely perceptible signal to 9 for extremely strong signal. Here also, radio amateurs tend to give liberal reports. Special situations are satellite operations and contests. In contests no one gives a report below 9! Similarly, in LEO satellite operations, every one gives a report as 5,9 rega...

 I still have the sweet memories of working a lot DX on CW in late 1980s using my homebrew 3 x 807 radio. That was a great upgrade from my 5W VU2VWN QRP which I homebrewed as soon as I got my amateur radio license in 1985. As the power supply, I was using a 600 V AC transformer made by a local ham and I had homebrewed the solid state bridge rectifier circuit with four diodes and large high voltage capacitors. In those days, I had sourced 807 valves from a local radio shop and if I remember correct, they were made by RCA. 807 is a beam tetrode vacuum tube which used to give me 40 W power each so that my TX was 120W on CW. In those days, 807 vacuum tubes were also being used in audio amplifiers, and that is how I could get them from a local radio shop. Even at that time, vacuum tubes were being phased out as solid state audio amplifiers had become commonplace. For AM, I needed a lot of audio power for modulation and I had homebrewed a solid state audio amplifier for that. But AM was ...

 Acrobatics of Working and Recording Space Station Pass!

 Some of my friends have been able to work 10m band over the past few days and I was on the lookout for stations on 10m. I heard a couple of DX stations on 28.475 MHz signing off, but I could not get their callsign. Though I tried calling QRZ, I did not get any reply. Later I heard a very strong station in foreign language on 28.506 MHz working a couple of other stations. After listening for a few minutes, they faded away before I could try a call. Then I came back to 28.475 MHz and gave an automated CQ call. Immediately I got a reply from YC2DOT from a distance of 4343.3 km, at 6.02 pm local time here. We had a quick exchange of reports and he said 73s. As I had not expected a reply as I seldom get replies for CQ calls, I could not record the QSO. After that I tried a few automated CQ calls with recording, but was not lucky to get any more contacts. Anyway I am happy that I could work one DX and hear a few DX on my erstwhile favourite DX band. Some of my DX friends had told me onl...

 Ever since I came back to HF in January 2024, my friends have been advising me to go for a linear amplifier. In VU land, the General Class licence which I have, has permission for 400 W power, though my radio can only give me 100 W. Almost every other operator who I hear on 40m has a linear amplifier. Then what is it that prevents me from going for a linear RF amplifier to boost my signals? When I came on air with my FT-710 radio with full power of 100 W, there were many on 40m who asked me whether I was using a QRP radio! The reason was simple, I was new to commercial radios and did not know how to adjust the radio. I had kept mic gain low and the processor level also low and I was scared of using the built-in automatic antenna tuner because of the rattling noise it makes! When I increased both mic gain and processor level and started using the auto-tuner, others started hearing me better. Then that was not all. My antennas were highly compromised due to space limitations. ...