Johnson's Techworld

 An ideal long wire antenna is one which is several wavelengths long. But that is not practical for most amateur radio operators. Sometimes it is also called as a random wire antenna because of the random length which is involved, though strictly not correct. In any case, a long wire antenna has to be at least quarter wavelength or better one full wavelength of the operating frequency. But wires at even multiples of quarter wavelengths will have very high feedpoint impedance which cannot be matched with an antenna tuner. Hence it is important to avoid even multiples of operating wavelengths. Long wire antenna is in fact an end fed wire antenna, typically matched with a tuner. Mounting should be as high as possible, for better performance. This method is often used during portable operations where the antenna can be mounted between branches of tall trees in the wild. Long wire antennas can be mounted horizontally, vertically or in a slope, depending on the local situation. The l...

  IC 2730 is a full duplex radio with two VFOs. You can tune to either VHF or UHF on either of the two VFOs. Transmit mode is available in the VFO selected as the Main band. The other VFO will continue to receive signals while transmitting using the main VFO. That is why it is called full duplex radio. There are two speakers with separate volume controls connected to the VFOs on corresponding side. If the speaker volume is kept too high during transmit mode, feedback howling can occur.

 We have discussed tuned radio frequency receivers and superheterodyne receivers . Among superheterodyne receivers we have seen both upconverting superhets and the conventional downconverting superhets. Another type of radio receiver is the direct conversion radio receiver, which though invented in 1930s, was impractical with the technology available then. With advent of modern integrated circuits and software defined radios, it became possible to implement direct conversion receivers, which find application in mobile phones, televisions and medical imaging as well as in software defined radios . Direct conversion receivers are also known as homodyne, synchrodyne or zero-IF receivers. They demodulate the incoming radio signal by using synchronous detection and hence the name synchrodyne. Direct conversion receivers use a local oscillator frequency which is identical to or very close to the carrier frequency of the received signal so that no intermediate frequency or IF is generat...

 I used to work on 80m in late 1980s when the solar cycle started going down and propagation on 40m started deteriorating. I made necessary changes in my homebrew 3 x 807 TX and used my Philips Prestige BC radio as RX. I could tie an 80m dipole on top of tall coconut trees at my parents' QTH then. I could work local stations on CW and AM and used to check in to the EC (East Coast) Net at 10 pm regularly controlled by VU2TTC (SK) and others. Currently I am told that EC Net is no longer there. Only net on 80m currently is the morning net on 3.6 MHz at 7.15am. Today I was having a QSO with VU3WEW on 7.1 MHz when he told me that 80m net is due and moved to that frequency. I listened to 3.6 MHz with my 40-10m combination inverted V dipole antenna and could hear VU3WEW, VU2MIE and later VU2OJ. Tried the autotuner of my FT-710, it would not tune to that frequency. Later I tried with my shortened EFHW for 20-10m, which also did not tune, as it had only 10m of wire up. On coming back to...

 Yesterday evening I tuned to 20m with my shortened end fed half wave antenna mounted using 3m PVC/CPVC pipes on my first floor terrace. To my surprise several stations were coming in unusually strong. I could hear VU3RAZ and VU2YK along with S79VU having a technical discussion. Tried to get in as VU3RAZ usually hears my break-in calls very well. But it was S79VU who picked my call first this time! As the discussions were continuing in full swing, suddenly V85NPV started calling S79VU. After exchanging reports with him, S79VU asked me to try calling V85NPV. I was quite happy as I have never worked Brunei Island. I had a quick QSO with V85NPV and he signed off after exchanging reports with all in the group. Interestingly, S79VU is also a new station in my log, though I have heard others work him earlier. Propagation was not good for me to work him then. I still remember hearing the broadcast station FEBA, Seychelles on shortwave while I was at school. Yet this is the first time I am...

 Stability of an oscillator is the degree of uniformity of frequency of the oscillator when measured over time. Frequency can change with change in conditions like temperature, load and supply voltage. For better stability of oscillators, temperature, load and supply voltage should be stabilized. Load can be stabilized by using buffer amplifiers between the oscillator and power amplifiers. In my early era of homebrewing in amateur radio, drift in frequency of the variable frequency oscillator was a tough problem to handle. Drift in frequency of the oscillator would cause difficulty to other stations listening to us as they had to continuously track our transmit frequency by manual tuning of the radio. When there were multiple stations on a round table, if the frequencies of each station drifted, that would be a real mess and could cause interference to stations working on adjacent channels. Drift in frequency could be due to change in inductance and capacitance in response to envir...

 Just tuned in to HF bands on my FT-710. Nothing heard on lower bands or WARC bands. 21 MHz was the most active band with plenty of CW signals on the waterfall, some very strong as well. But none of them are within my reach, too fast for me to even attempt decoding. Quite a few signals are also there on 28 MHz which has been a 'dead band' for me for the past few months. Both the ' Winter anomaly ' and the 'Contest anomaly' seems to have boosted the 10m band at my end. Enjoying the display on the waterfall, though I have not been able to get any one of them in the log so far.

 Lamakaan Amateur Radio Club at Hyderabad, India, which I would call the birthplace of popular BITX QRP SSB radio, is hosting the most anticipated event Lamakaan Annual Radio Convention or LARC-7 , on 14th and 15th December 2024. LARC is an annual event usually held on the 2nd Saturday and Sunday of December every year. It is a great opportunity for radio amateurs to showcase there experimentation with newer radio techniques, building radios and antennas as well as interacting with fellow hams across the region and the globe. There are plenty of workshops, talks, forums and contests planned for LARC-7. You can assemble the sBITX version 3, an upconverting superhet with multi-band TX at LARC-7 and the workshop is being conducted by VU2BVB. You have to provide your own monitor, keyboard and mouse while the basic kit for sBITX can be bought at the convention. Another workshop by VU3DX is for you to build a two line LCD display for uBITX v3. Next one is assembling uBITX 6, a...

  There was a pass of Space Station from North to South along the Eastern side today evening at around 6.45 pm IST. So I kept my Moxon Yagi in a North East direction, hoping to pick up some station from that direction, even though it was only a pass of about 18 degree maximum elevation, which is not that good for my suboptimal setup. Moreover, I was pointing my antenna almost at my water tank which was higher than the antenna and made of solid concrete. Still I could hear VU2TUM fairly well at the beginning of the pass and VU2YE later. As the satellite reached the Eastern side, I heard a YD station and wanted to 'catch' that station. As the satellite direction was already away from the antenna, I quickly went outside and rotated my Moxon Yagi to the Eastern direction, taking about 30 seconds to do so. When I came back, I could hear VU2YE much more clearly and DX station could be heard partly once again. I could also hear VU3BGK. Here is the curated audio recording of the pass:

 PIN diode is a diode with an additional undoped region of intrinsic semiconductor. Usual diodes have P and N types of semiconductors meeting at a junction. For PIN diode, the I or intrinsic region is between the P and N type regions. The P and N type regions may be heavily doped and used for ohmic contacts. The intrinsic region makes a PIN diode inferior as a rectifier compared to PN diodes. But PIN diodes are suitable for attenuators, fast switches, photodetectors and high voltage power electronics applications. Intrinsic region is flooded with charge carriers from P and N regions in what is known as high level injection. PIN diodes will conduct current once the flooded electrons and holes reach an equilibrium point with equal number of electrons and holes in the intrinsic region. While the PIN diodes functions like a standard diode at low frequencies, it works almost like a perfect resistor at high frequencies even for large signals. The high frequency resistance is inversely pr...

 I have noted that most of the new hams getting licensed in this region are VU3 rather than VU2. You are aware that VU2 has much more exciting operating privileges than VU3. As of now, most of you with VU3 have been finding it difficult to crack the Morse Code test. Shall we start practise sessions on air? My simple suggestion is that we can use local repeaters which are idle most of the time for live Morse Code receiving sessions. Being FM repeaters, we can start the call on voice and send recorded CW messages as audio, just like the repeater beacon, at slow speed so that those listening can copy them and call back on voice, confirming the reception. I have noted that most VU3s are able to send CW well while they have difficulty in receiving. It is this aspect which we plan to help out by these sessions. Currently I can access only VU2CSR and VU2MJJ repeaters. Others with access to other repeaters could try it out in their regions so that more and more VU3s can upgrade to VU2 and ...

 An ESD (electrostatic discharge) protection diode is a type of Zener diode optimized for ESD protection applications. They are a simple and low cost way to protect electronic circuits from release of stored static electricity on common touchpoints like USB ports and buttons. There are diodes for a wide range of signal voltages with protection up to 30 Kilovolts! A slightly different device is a TVS or transient voltage suppressor diode which can protect from lightning surges, switching surges and signal ripples. ESD protection diodes remain silent in the absence of electrostatic discharge. They protect integrated circuits in the event of an excessive electrostatic discharge. An ESD diode is a type of PN semiconductor junction designed to be used in reverse bias. Beyond the avalanche breakdown voltage, avalanche breakdown as discussed in the case of TVS diodes occur and that voltage can be called Zener voltage. Zener voltage can be optimized by the dopant densities in the N and P...

 Well, I had not heard till I read the program schedule of LARC-7 today. Most of you would be familiar with uBITX which has gone up to version 6. Some of you would be aware of sBITX, which is quite an advance over uBITX. Almost daily I am meeting a new uBITX user on the band, most of them using additional linear amplifiers. That made me join the BITX group on groups.io , where I am getting messages from uBITX and sBITX users from all sides of the globe. Still I was not aware of zBITX and that made me look around and came across two references. One was the video of a talk by VU2ESE at QRP ARCI . Another was an email in the BITX groups.io which was citing the former. zBITX is a new transceiver from VU2ESE based on Raspberry Pi Zero for 20W, having CW skimmer and FT8 modes in addition to the regular SSB mode and waterfall display which the sBITX also has. zBITX is quite small, just 3" x 3" x 1.5" in size. It is a Raspberry Pi Zero based 20 W software defined radio which h...

 Slim Jim antenna, as the name implies, has a very slim design and hence very little wind loading. JIM stands for "J Integrated Matching" as it uses a J type matching stub. Slim Jim antenna was described by Fred Judd, G2BCX in 1978. The antenna has a lower takeoff angle and hence reported to have better performance than 5/8 wavelength ground plane antenna. People have made it using half inch copper pipe, ladder line and many other options! Approximate gain in the horizontal plane has been mentioned as around 2  dBi. Slim Jim antenna should be insulated from the antenna mast with a 'free space' of at least quarter wavelength. Antenna itself can be supported on a PVC pipe. Though it can be made for any band, it is quite popular as a 2m VHF antenna which can be made easily with good performance. It is almost like a vertical asymmetric folded dipole with a gap between the half wave and quarter wave regions. The exact feed points on the long and short parts of the antenna ...

  Inverted V antenna was the first ever antenna I built nearly four decades back, with a two copper wires and a wooden pole. It was fed by just 75 ohms television cable, as that was only what I had then. Inverted V is the most popular HF antenna among new hams because it is easy to build and needs only a single high support in the middle. Both ends need to be taller than human beings to avoid accidental contacts and possibility of difficult to heal RF burns. In this review I will go through theoretical aspects as well as how I built an inverted V antenna recently. A combination inverted V dipole for 40 and 10m can work on 40, 10 and even 15m band as the third harmonic of 40m band. As a tailpiece, I have added a rare instance of working the cross-band repeater on International Space Station using it, though it is not the ideal method of working amateur radio satellites.

 Covering almost everything an amateur radio operator should know about SWR or standing wave ratio. Takes you through the basic concepts about SWR, how to connect the SWR meter to your radio and measure SWR, modern radios with built-in SWR meters and automatic antenna tuner, and finally, whether you should worry be too much about the SWR with modern radios.

 My quarter century old TH-22 AT hand held radio had been in shelf for quite long. Battery pack was misplaced and I had a battery box supplied by the manufacturer. Stock rubber duck antenna was also misplaced. When I tried with four dry cells in the battery box, it would not get switched on. On opening up the radio, I found that the battery contact for the battery box had broken and one piece was missing. The connectors were also corroded. Now I have tested by connecting an external battery box and an external power jack and to my surprise, the handheld transceiver got switched on! Next step is to find out an antenna and test the radio in full.

 My amplispeaker cum FM radio does not have a volume control. So receiving FM stations can be a distraction to others at home. As I want to experiment further with FM radio antennas, I thought of fixing a volume control. When I opened up the amplispeaker I found that it is all surface mount technology and I was not confident of meddling with it. Decided to fix a potentiometer for volume control to the speaker directly. But I did not have a low value potentiometer to directly control the speaker which would be only about 8 ohms. That is how I decided to use the 'Pencil Potentiometer' which I had improvised a few days back!

 TVS diodes or transient voltage suppression diodes are electronic components used to protect electronic devices from voltage spikes induced on connected wires. TVS diodes acts by shunting excess current when the induced voltage exceeds the avalanche breakdown potential. It can be considered as a clamping device suppressing all overvoltages above its breakdown voltage. Electron avalanche occurs when electrons are accelerated by electric energies and collide with atoms to create more mobile electrons and ions which can lead to high currents beyond the breakdown voltage. Incidentally, I came across the use of TVS diodes in a discussion on BITX forum, where it was mentioned that TVS diodes are used for gate protection of final MOSFETs! TVS diodes can be unidirectional or bidirectional. The first device seen in the image is a unidirectional TVS diode and can be recognized by the band in the region of the cathode, while other devices are bidirectional and do not have the band. Schematic...

 Last year I had posted that AMSAT-OSCAR 7 (AO 7) was nearing its Golden Jubilee. AO-7 has completed 50 years of operation as an amateur radio satellite on 15th November 2024, having been launched in 1974, three years earlier than Voyager spacecrafts which are now travelling in interstellar space. Initially it was expected to function for just three years! In fact I read that battery failure had caused it to become non-functional in 1981. But luckily, the shorted batteries became open circuit in 2002 so that it could work on solar panels. It had two transponders, A and B, of which transponder A had uplink on VHF and downlink on 10m. It was a non-inverting linear transponder. A few reports of telemetry being still active on transponder A are there on AMSAT Live OSCAR Satellite Status Page . At the same time, there are plenty of reports of both uplink and downlink being active for transponder B. Transponder B is a U/V transponder with uplink on 432.125 - 432.175 MHz SSB/CW and is an...

 Folded dipole can be considered as a  dipole antenna  on top of which a loop of conductor is added so that it will be short circuiting any direct current fed to the antenna, though antennas are typically fed with alternating currents. Folded dipole is a balanced antenna and has to be fed by  balanced feeder  like a twin lead ladder line. If a coaxial cable is used to feed the folded dipole antenna, a  balun or balanced to unbalanced transformer  has to be used. While the usual half-wave dipole antenna has an impedance of about 70 Ohms, folded dipole antenna has an impedance of around 280 Ohms. So it matches well with a ladder line of 300 Ohms impedance. Earlier twin lead ribbon tapes were used to connect the folded dipole television antenna to the television receiver. Folded dipole antenna has a higher bandwidth than the usual half-wave dipole antenna. Coax balun is a simple way for eliminating feedline radiation which would occur if dipole is fed by ...

Circuitry inside TH 22AT I had posted about my quarter century old TH 22AT radio a few days back. Now I am trying to figure out how to open it up and look inside to see if I can do anything about or at least find out what is wrong inside. You can go through my efforts at opening it up gradually and then assembling it back again.

 Well, I had not heard of an upconverting superhet till I read about sBitx transceiver from VU2ESE . Usual superhets which I have heard of were downconverting superhets which downconvert the received frequency using a local oscillator and mixer to a lower frequency known as intermediate frequency or IF. There are single conversion, double conversion and triple conversion superhets depending on the level of sophistication of the superheterodyne receivers. Multiple conversions give better selectivity and image frequency rejection. Single conversion is often a compromise between selectivity and image frequency rejection, as discussed earlier. Interestingly, sBitx is an upconverting superhet with IF at 40 MHz, much above the 455 kHz of single conversion superhets and higher frequencies of superhets with multiple levels of conversion. The advantage mentioned is that upconversion and use of higher IF eliminates the need for multiple filters, one for each band of operation. As HF operato...

 Many of you would have heard of Arduino, the popular microcontroller, especially those interested in hobby projects and those who are using the Arduino based µBITX QRP transceiver. Some of you would also have used Raduino in your µBITX QRP transceivers. Raduino is a free platform for creating wireless sensor networks, including hardware, firmware and software based on the Arduino platform. This may allow even people without much programming experience to build their own sensor network. Raduino project originated in Brazil in 2010 and is an extension of the Arduino project which started in 2005. Hardware part is an Arduino integrated with a CC1101 transceiver and controlled by an ATMEGA328 microcontroller. CC1101 is a low cost sub 1GHz transceiver for very low power wireless applications. Versions for 433 MHz and 868 MHz could be seen as available online in this region. ATMEGA328 is a microcontroller commonly implemented in the Arduino platform. Raduino circuit board supplied with ...

 Today I had the opportunity to check in to a unique type of HF net, the BCDX Net on 7085 kHz. As I came a bit late to the band today, I was looking at the waterfall display for any stations to work. I saw a signal on 7085 kHz and thought that Lake City Net has been quite delayed. But the Lake City Net had been over and it was the BCDX Net. I heard VU3XIO reading out a list of broadcast stations and their signal reports. I listened because I had been a BC DXer in a small way before I came to amateur radio. I used to tune around the Phillips Prestige vacuum tube radio during free time, looking for long distance stations. BCDX net is only on Sundays, from 8.30 to 9.00 am and the net controls are from my place, VU3SIO and VU3XIO.

Inside view of amplispeaker cum FM radio  My amplispeaker cum FM radio does not have a volume control. So it is hard to use it when a strong FM station is being heard. I thought of adding a volume control and opened up the speaker box to see how I can do it. To my surprise, I found that it the dual sided printed circuit board uses surface mount technology and not through the hole technology. I have never worked on SMD and hence I dare not meddle with this one. Only way out for me will be to try and fix a low value potentiometer to the speaker to see if that helps in controlling the volume. Currently I do not have one and I plan to work on it later if I can get one!

 Here is a simple circuit with 74HC14 Hex Inverting Schmitt Trigger IC. Different values of capacitor can be tried to change the blinking rate of the LED. Though 74HC14 has six Inverting Schmitt Trigger gates (NOT gates), only one is being used in this demo circuit which functions like an oscillator. Checking of LED, resistors and capacitor have been shown during the process of assembling the circuit on a solderless breadboard.

  Simple Dipole Antenna for FM Radio As I did not have a regular FM radio, I thought of using an amplispeaker which could work as an FM radio if the mic with long cord was connected. I describing how I made a simple dipole antenna for FM reception using a 1m long speaker wire with connectors which I already had in my shelf. As part of the material was already in hand, it could me only a few minutes to shape the speaker wire with 75 cm on either side for a 100 MHz half wave dipole. The remaining 25 cm was the 'feedline' to the speaker cum FM radio which I had here. I am planning to try out with a longer cable or twisted flex to mount the dipole higher as a follow on project soon.

Every radio amateur should know about the basics of a radio transmitter, whether you are going to operate a commercial one or make one on your own, what we call by the pet name 'homebrew'. A radio transmitter is a device which generates a radiofrequency signal and sents it out as radio waves through the antenna. If only the radio frequency carrier wave is sent with breaks and makes corresponding to Morse Code formerly used in telegraphy, then it is known as a CW (Continuous Wave) transmitter, which is the simplest one. Like many other radio amateurs in the yester years, I had also homebrewed a basic CW transmitter using BD139 transistor as the final RF amplifier, running about 5W, known as QRP transmitter. Initial part of the transmitter is the radio frequency generator known as oscillator, which produces a high frequency oscillating current when you supply it with a direct current power supply. Oscillator section was called a VFO or Variable Frequency Oscillator as the freque...

 LignoSat developed by Kyoto University, Japan and the logging firm Sumitomo Forestry aimed at using wood for space exploration! Ligno stands for wood in Latin and you would certainly remember Lignite, a form of coal, from your school days. LignoSat has been made of wood from honoki, a magnolia tree native in Japan. Choice of material was determined through a 10 month long experiment onboard the International Space Station. It has been assembled through a traditional Japanese crafts technique without screws or glue. That is rather surprising, to assemble a satellite without screws or glue! Of course, it has some traditional aluminium structures and electronic components as well, without which it will not be able to function as an amateur radio satellite for communication. First in the series, LignoSat 1, is a one unit cubesat with 10 cm for each side and weighs just 900 gm. It was sent to the International Space Station onboard Dragon capsule by SpaceX's Falcon 9 Block 5 rocket. Li...

This week, every amateur radio satellite enthusiast is busy decoding and posting SSTV (Slow Scan TV) images from International Space Station. Now what is SSDV? SSDV is the abbreviation for Slow Scan Digital TV, in contrast to SSTV which is analog and has been there for a long time. It has been mentioned that SSDV is a packetised digital form of SSTV. I heard of SSDV first when I read about the recently launched ASRTU-1 amateur radio satellite, which has a UHF SSDV in addition to the V/U transponder and 10GHz high resolution image downlink onboard. UBSEDS24 Balloon with SSDV launched from Bristol, UK sometime back had recorded nice SSDV images of the clouds from above. Lunar-OSCAR-94 which went into lunar orbit had transmitted SSDV images back to radio amateurs on Earth. WSJT JT4G was used for messages and transmissions were on 435.400 and 436.400 MHz. Transmitting power was about 2W, using VHF/UHF SDR transceivers. It was the world's smallest spacecraft to enter lunar orbit indep...

  Yesterday, I had mentioned that I was quite happy when I came across a BD139 transistor in a voltage stabilizer brought back after repair. That was because I remembered my early days in amateur radio, way back in 1985, when myself, VU2VWN (SK), VU2JOS and many others in this region used to operate the then popular VU2VWN QRP. As soon as I received my amateur radio licence, it was VU2NYR (SK), who gave me the circuit diagram of VU2VWN QRP and gave me guidance to homebrew it, tie up an inverted V antenna and come up on the band on CW. My callsign in those days was VU2JFP, with a grade 1 licence. My current callsign VU2JO was obtained after upgrade to advanced grade in 1988. My first contact on 40m after homebrewing the circuit was of course VU2NYR as we fixed a sked over telephone. When I started coming on band regularly, VU2VWN and VU2JOS were there regularly on air as well, and VU2VWN used to give guidance to fine tune my setup. Later I added a modulator to the CW QRP and started...

 Yesterday I was trying to check in to AIRNET India at 7.30 pm and I could hear the net control very strong, at 5,9+20 dB. Pressed the PTT to announce my callsign when the call for any more check-ins came through. Immediately 'HI SWR' was displayed in the meter in red colour and there was no output from the radio. Tried tuning with built-in auto tuner of FT-710 and the tuner refused to tune. Switched to 21 MHz and tried auto tuning and it did tune to one frequency. I was confused and went outside to check the antenna. As it was dark, I first checked the portion of the antenna wire and mast from the front side and it seemed OK. At second thought, I went on to the first floor terrace and checked and there it was, the other limb of the 40m dipole was down! The nylon thread which had been used to tie the antenna had given way. So the lesson is, whenever you see a 'HI SWR' display on your screen with a previously functioning antenna, go out and check the antenna in full.  Wa...

  I am quite happy to receive this picture from Amateur Radio on International Space Station using my homebrew Delta Loop VHF antenna just now. One of the best pictures I have decoded ever with my setup! In case you wish to have a look at the antenna, it is here: https://youtu.be/ySYL96zvvOs . It was a 75 degree pass.

  Demo of the method to receive SSTV from Space Station on 145.800 MHz during a pass of the space station. Timing and direction of the pass can be found from https://www.n2yo.com/passes/?s=25544# . Doppler tuning needed can be found at: https://mail.amsat.org.ar/pass.htm . In good elevation passes, simpler antennas and reception without Doppler tuning might work. Decoding is by Robot 36 app in mobile phone kept near the speaker of the radio. Alternatively, recorded audio can be decoded later using the Robot 36 app. Directional Yagi antennas will decode better pictures if moved along the direction and elevation of the pass.

 An SSTV (Slow Scan Television) event from International Space Station is scheduled to start at 11:50 UTC on 11th November 2024 and will continue up to 18th November 2024. So there is plenty of opportunity to tune in to 145.800 MHz during the space station passes in our region and try to record the audio as well as decode SSTV images using Robot 36 app in our mobile phone in PD 120 format. As the transmissions are at relatively high power, most VHF reception setups will be able to get at least part of the SSTV images. Last time I could get partial copy even with a magnetic mount VHF antenna kept on my linear power supply. Ideal method of course, is to use a directional antenna pointed in the direction and elevation of the pass of space station continuously. But many of us may not have that. Doppler correction is also useful, but not mandatory to receive some images in high elevation passes. I had used my recently homebrewed VHF Delta Loop antenna for local repeater contacts and a ...

 Some time back we have a Google Meet on Fldigi in our LEO Satellite Group, conducted by VU2TUM. Thought of brushing it up once again when VU2NXG told me yesterday that Fldigi can be used for RTTY mode, though I am yet to try it out. Fldigi known in full as Fast Light Digital, is a cross-platform modem application which supports most of the peer-to-peer digital modes used on amateur radio bands with live keyboard. Fldigi allows the sound card of a computer to be used as a simple two-way data modem. It is a free and open source program which can be downloaded from sourceforge.net . Fldigi supports CW or Morse Code operation using a computer keyboard and Radio Teletype known in short as RTTY and many other modes which I am not familiar with. The program was written by W1HKJ who has also authored several other amateur radio programs. There is a nice Beginners' Guide to Fldigi written in simple language. But to make the best use of the program, one has to read the Online Documentati...

 I had posted about LMR SDR a couple of days back. LMR SDR covers from 160m to 10m band and gives an output of up to 50 mW which has to be amplified further using a linear amplifier, if needed. It is based on Arduino Nano microprocessor and Si5351 programmable clock generator. A computer and sound card are needed for the operation of the basic version of LMR SDR and uses PowerSDR software. Yesterday VU3GEX told me about standalone versions of LMR SDR which do not need a computer. He mentioned that ESP32 and STM32 can be used in Standalone LMR SDR. STM32 is a family of 32-bit microcontroller integrated circuits by STMicroelectronics. ESP32 is a series of low-cost, low-power microcontrollers. To my great surprise, a search for ESP32 Standalone LMR SDR brought me to RDvibes , a website by VU3ZOF, whom I have been hearing and talking to on 40m for the past few days. According to the website, the standalone variant was developed by YD1GSE and uses ESP32-A1S processor. The exciter front...

  Simple way of making a variable resistor with the graphite (carbon) inside a pencil. I my childhood, pencils used be called lead pencils, though I have never seen lead inside pencils, it was all graphite. Maybe it was there earlier and that was the reason for the old name. Colour pencils seem to be made of something else. I had checked continuity of some colour pencils and found it beyond the range! Not sure whether they could be used for high value potentiometers. I have not checked.

 When there is no signal being received, a sensitive receiver can produce significant noise because automatic gain control disappears in the absence of any carrier. Receiver becomes more sensitive and amplifies any electrical noise present in the input. This especially more in FM receivers which produces a hissing noise when the squelch is kept open. The circuit used to quieten the noise while no signal is being received is known as squelch. Usually a volume control like mechanism is used to adjust the squelch level. While receiving weak signals of amateur radio satellites, squelch is intentionally kept open as the weak signals from satellites may not be enough to open the closed squelch. Powerful signals from satellites like the amateur radio on international space station may be able open squelch in high elevation passes when the satellite comes near overhead.

 Some important features to be looked at in a radio receiver are its sensitivity, selectivity, fidelity, adjacent channel and image interference, automatic volume control (AVC), squelch and signal to noise ratio. Sensitivity is the ability of the radio receiver to pick up weak signals. Lower the signal needed in the antenna circuit to have good audio output, higher the sensitivity of the radio. Sensitivity may range from microvolts to millivolts of signal in the antenna circuit and depends on the number of amplification stages in the radio and their quality. Selectivity is the ability of a radio receiver to separate the signal of the intended station from those operating on other frequencies. We need the reception bandwidth to be narrow. Yet it should not cut off the upper and lower audio frequencies modulating the received signal. Selectivity can be improved by having more tuned circuits of higher quality in the receiver. Fidelity is the quality of reproduction of the received sig...

 We have seen that usual superheterodyne radio receivers have single conversion of received frequency to the intermediate frequency using a single local oscillator and mixer. In many of the modern communications receivers, multiple successive stages of frequency conversions with multiple intermediate frequencies are used. A receiver with two frequency conversions and two intermediate frequencies is known as a double or dual conversion superheterodyne receiver. One with three levels of conversion and three intermediate frequencies is known as a triple conversion superheterodyne receiver. Use of additional conversions improve adjacent channel selectivity and image frequency rejection. First IF stage has a wide separation between the intended signal and the image frequency, enabling RF amplifier to reject the image frequency. Second IF filter has a narrow bandwidth providing good adjacent channel selectivity. Single IF stage in conventional superheterodyne receivers is a tradeoff betw...