Portable Ham Antenna Uses SMD Capacitors

[K6ARK] likes to operate portable, so he puts together very lightweight antennas. One of his latest uses tiny toroids and SMD capacitors to form trap elements. You can see  the construction of it in the video below.

You usually think of toroid winding as something you do when building transmitters or receivers, especially small ones like these. We presume the antenna is best for QRP (low power) operation since the tiny core would saturate pretty quickly at higher power. Exactly how much power you should pass through an FT50-43 core depends on the exact application, but we’ve seen numbers around 5 watts.

 

The SMD capacitors mount right inside a hacked up BNC connector. That makes for a very compact construction at the expense of a little fine work with a soldering iron while building. There is more construction detail on similar traps in a second video that you can see below.

The availability of antenna analyzer equipment makes projects like this easier. The concept of end-fed halfwave has its detractors and proponents. [AA5TB] has a page that explains a bit about the theories surrounding the antenna. Regardless, [K6ARK] says he’s worked the world on this type of antenna and many people swear by them.

Not a ham yet? [Dan Malone] wants you to invest $50 and change that. We suspect, though, you’ll be happier with more wire in the air.

Product Review: The TinySA, A Shirt-Pocket Sized Spectrum Analyzer

I suppose most of us have had the experience of going to the mailbox and seeing that telltale package in the white plastic bag, the sign that something has just arrived from China. This happened to me the other day, and like many of you it was one of those times when I puzzled to myself: “I wonder what I bought this time?”

With so many weeks or months between the time of your impulsive click on the “Buy Now” button on AliExpress or eBay and the slow boat from China actually getting the package to your door, it’s easy enough to forget what exactly each package contains. And with the price of goods so low, the tendency to click and forget is all the easier. That’s not necessarily a good thing, but I like surprises as much as the next person, so I was happy to learn that I was now the owner of a tinySA spectrum analyzer. Time for a look at what this little thing can do.

 

First Impressions

A caveat: I’m by no means an expert on spectrum analyzers. In fact, this is the first time I’ve ever handled one, unless you count using the FFT functions in my digital oscilloscope, which you probably shouldn’t. So there’s probably plenty of room for operator error and misconceptions about what a spectrum analyzer can do in the tests that I ran, but I still think this is valuable as an example of what a tool like this can do in the hands of an enthusiastic newbie.

Anyone familiar with the NanoVNA, a small but full-featured vector network analyzer that we’ve featured a few times on these pages, will see a strong family resemblance between it and the tinySA, both in the hardware and the software. That’s for good reason — the code behind tinySA is a fork off the NanoVNA codebase, and the main developer of NanoVNA, edy555, is a contributor to the tinySA project, which is owned by Erik Kaashoek.

The tinySA arrived in a surprisingly nice “presentation quality” box with a gold-stamped logo on the top. Erik takes pains to note that this is one way to tell you’re getting an original tinySA as opposed to one of the inevitable knock-offs that’ll flood the market soon enough. I’m not sure that alone would keep the pirates at bay, but it’s at least an attempt and it’s a nice touch to boot.

Along with the tinySA, which is about the size of a deck of playing cards, the box contains a pair of SMA jumper cables, a small telescoping whip antenna, a female-to-female SMA adapter, a wrist strap, and a USB-C cable. The case of the tinySA is injection molded ABS, and a nice upgrade in look and feel from the open board design of the NanoVNA. The front of the tinySA has no controls, just the 2.8″ 320×240 resistive touch-screen display. The top has a power switch and a jog control. The left side has two SMA jacks, labeled HIGH and LOW. It’s very lightweight but feels solid in the hand.

A look inside the tinySA, with the RF shields removed.

Of course the first thing I did was pop the case open and take a look inside. There’s not a lot to see at first — most of the interesting RF stuff is safely tucked under shielding. I figured I’d have to bust out the Hakko to take the tins off, but luckily they’re all spring-clipped to the ground plane, so removing them just took a small screwdriver. Underneath lay the expected RF wizardry, including the expected Silicon Labs chips. I found two Si4432 ISM transceiver chips, presumably one each for the high and low range of the tinySA. There’s also what appears to be a Peregrine Semiconductor PE4302 RF digital attenuator, and a bunch of other goodies. The layout is nice with plenty of via stitching, and the assembly quality is really good.

Satisfied with the insides, I moved on to the “First Steps” as listed in the video below, to get acquainted with the device. Erik has chosen to rely on the tinySA wiki and some how-to videos for most of the documentation, and while that’s understandable it also leaves a few holes that are up to the user to fill in. For those of us who prefer a real manual, Kurt Poulsen, a ham from Denmark, has written up a comprehensive how-to document that might be of help.

Anyone who has used a NanoVNA will feel at home in the tinySA interface. Calibration of the tinySA is done via the built-in signal generator, more on that below. Calibration itself is simple: hook the jumper coax between the two SMA jacks and select LEVEL CAL from the configuration menu. The calibration then proceeds automatically. The same menu offers a self-test function too, which cycles through a series of ten tests that take about 15 seconds to complete.

The Good Stuff

As for its primary purpose, the tinySA performed admirably in my limited tests. I took a look at the spectrum of signals generated by my scope’s built-in waveform generator and everything looked good — a 10-MHz sine wave appears as a single strong fundamental spike and one harmonic about 50 dBm lower. Switching the waveform to a square wave at the same frequency did what I thought it would — a big peak at the fundamental and a bunch of spurs at the odd fundamentals.

Output from the tinySA on my scope – solid, clean 10-MHz sine signal.

With the basics out of the way, I took a look at the tinySA’s built-in signal generator. As mentioned above, the signal generator is used for calibration, but it’s a pretty capable tool all on its own. It’s actually more of a function generator, since it can not only output a nice clean sine wave on the low output between 100 kHz and 350 MHz, but it can also modulate the signal (AM, narrow FM, and wide FM) and do sweeps both across a frequency range and over amplitude. On the high output, the signal generator does a square wave output from 240 MHz to 960 MHz with a configurable, non-sweepable amplitude, narrow FM or wide FM modulation, and a frequency sweep.

I gave the signal generator a go and took a look at its output with my Keysight DSOX1102G. The sine wave generated on the low output looked clean across the specified bandwidth, and the frequency was spot on. I tried playing with the modulation function, and it worked pretty much as I expected. It’ll be nice to have another signal generator around the shop.

My janky test setup: UV-5RA, homebrew 40 dB attenuator, and the tinySA.

With all the pleasantries dispensed, I turned to the one task pretty much every ham will want to turn a spectrum analyzer on: finding out just how bad the signal from a cheap handy talkie is. I talked about this a bit in one of my $50 Ham articles, and we’ve seen comprehensive analyses of spurious emissions from these radios that are far more in-depth than anything I could come up with using the tinySA. But still, I thought I’d give it a whirl. I grabbed my Baofeng UV-5RA, a homebrew 40 dB attenuator I built a while back, and an unwieldy collection of adapters to connect everything together.

Being under the impression that the spurious emissions on Baofeng tend to be worse on the UHF band, I tried 420 MHz first. The first thing I noticed was that the fundamenal was off a bit from the where it should be. I also noticed a small forest of spurs starting at 500 MHz and extending all the way up past 800 MHz. The strongest spur was about 43 dBm down from the fundamental. The FCC rules on spurious emissions don’t seem to cover this band, but they do say that between 30 and 225 MHz, spurs need to be at least 40 dBm below the fundamental. So within the limits of my test setup, the Baofeng seems to just barely comply.

Spurious emissions from a Baofeng UV-5RA at 420 MHz. The big spur at about 825 MHz is the only one that comes close to exceeding the limits.

Just for completeness, I repeated the same test on the 2-m band. The signal was much cleaner here, with only a few spurs, the big one being at around 270 MHz. Again, this was about 43 dBm down from the fundamental, meaning it was probably in compliance. Again, this was only a rough test, with a test setup leaving much to be desired. But still, the tinySA is a nice way to take a look at what you’re actually putting out into the ether, and to at least get a rough idea how clean you’re operating.

A much cleaner signal from the same radio on the 2-m band.

The Not-So-Good Stuff

Like the NanoVNA before it, the tinySA has the capability of PC control. The Python program, TinySASaver, is geared mostly toward saving scans from the tinySA, but also provides additional capability, like doing frequency sweeps in segments and exporting data for further analysis. It also implements time-domain reflectometry (TDR) to measure cable lengths and find faults. Sadly, try as I might I was unable to get TinySASaver running on my Ubuntu machine. Erik is pretty clear that the code is still rough, and I’m far from a Python guru so I might be having library problems that would be easy to fix for someone with more experience. Luckily, I was able to scrounge up a decrepit Windows laptop and get a compiled version of another program running, so I didn’t have to resort to cell phone pictures for my screenshots.

I have noticed a couple of other annoying issues. The biggest is that the tinySA appears to crash when you click the screen off of one of the menus. This is annoying, as I often found myself stuck in a menu with no obvious “Back” button, and clicking on the background seemed like an intuitive way to work back to another menu. But this just throws a dump of all the registers up on the screen and locks the thing up. It’s not a huge deal to recover — toggle the power and it’ll boot right back up — but it can be annoying.This bug has been removed recently so this is working as it should by now.

I also found the touchscreen a bit finicky, which was a common complaint with the NanoVNA. The screen is far too small for my meathooks, but without a proper stylus, I resorted to a plastic spudger that worked only most of the time. Of course it was only then that I looked in the box and noticed the wrist strap with the attached guitar pick-like stylus — a thoughtful accessory indeed.

Verdict

I’m not entirely sure what I paid for the tinySA — like I said, I tend to order these things and then just forget about them. But I think it was around $60, and at that price I’d say adding a tinySA to your toolkit is a no-brainer. It’ll never substitute for a larger, full-featured instrument, but if your only need for a spectrum analyzer is to design the occasional filter or check signal quality, the tinySA is a pretty good deal.

QO-100 / Es’hail 2 thuis ontvangen

Op 15 november 2018 werd vanaf Kennedy Spacecenter de Es’hail 2 gelanceerd richting een geostationaire baan om de aarde en sinds enige tijd is de satelliet te gebruiken door radiozendamateurs.

Met een downlink op 10 GHz en een uplink op 2,4 GHz is de satelliet door amateurs betrekkelijk eenvoudig te gebruiken. Het blijkt dat het ontvangen van de satelliet eenvoudiger is dan gedacht. Thijs, PE1RLN neemt je graag mee in zijn ervaringen bij het ontvangen van de smalband communicatie.

10GHz omzetten

Het ontvangen van een 10 GHz signaal lijkt heel moeilijk maar is met behulp van wat hulpmiddelen erg eenvoudig. Elke satellietschotel heeft een LNB (low noise blockconverter) die het 10GHz signaal van bijvoorbeeld de Astra satelliet omlaag brengt naar circa 900 MHz, een frequentie die al beter te behappen is. Maar voor ons radiozendamateurs geen gangbare frequentie natuurlijk.

De LNB links op de foto kun je vinden bij Passion Radio en deze transformeert het 10 GHz signaal van de Es’hail naar 432 MHz ! Kijk, dan wordt het interessant.

De LNB is voorzien van een 0,5ppm TCXO voor goede stabiliteit en je krijgt er een bias-tee bij om de LNB te voorzien van spanning. Deze werkt namelijk op 12V via de coax. Bij 12V werkt de LNB op vertikale polarisatie, prima voor de smalband transponder. Bij 14-18V werkt hij horizontaal voor de breedband transponder. Voor € 80 heb je ‘m thuisbezorgd binnen een paar dagen.

De IC-9700 transceiver van Icom kan op de antenne-aansluiting ook 12V tijdens RX afgeven, dan heb je de bias-tee niet nodig.

De lokale oscillator in de LNB werkt op 10.057 MHz dus bijvoorbeeld het PSK baken op 10.489,750 MHz ontvang je straks op 432,750 MHz.

Schotel

Schotels zijn voor shoarma én om satellieten te ontvangen. Thijs had nog een 35cm campingschotel liggen en die bleek prima te functioneren voor ontvangst! Dus investeer niet in grote radiotelescopen, 35cm volstaat. Zorg dat je een stevig statief hebt want het uitrichten komt een beetje precies.

De LNB wordt voorop gemonteerd en wel zodanig dat deze een “skew” heeft van -15,9 graden. Dat betekent dat de LNB gekanteld wordt met de wijzers van de klok mee als je over de LNB heen naar de schotel kijkt. Dat heeft te maken met de kanteling (skew) van de polarisatie van de satelliet zelf. Hoe beter de skew is afgeregeld, hoe sterker het signaal.

Aansluiten

De LNB en de bias-tee zijn voorzien van F-connectoren, zeer gebruikelijk bij satelliet-TV. Thijs heeft achter op de schotel een BNC aansluiting gemaakt en heeft de bias-tee in een kastje ingebouwd met BNC-connectoren. De impedantie klopt niet helemaal en dat levert verlies op maar de LNB geeft zo’n keihard signaal af dat je dat prima kunt permitteren. Op de bias-tee zit zelfs een attenuator die het signaal dempt en die heb je zeker nodig.

De bias-tee komt dus tussen LNB en ontvanger (tenzij je ontvanger al 12V op de coax heeft) en dan stem je af op 432,750 MHz.

Met het stelknopje in de deksel kun je de attenuation instellen. Aangezien de coax kort is en de LNB een hard signaal geeft, kun je deze best zo instellen dat bij een normale RF gain je waterfall weinig ruis laat zien zodat signalen goed zichtbaar zijn. Dit is handig bij het uitrichten.

Uitrichten van de schotel

Stel de schotel bijna vertikaal en richt de arm van de LNB richting het zuiden. Draai vervolgens 26 graden naar het oosten (tegen wijzers van de klok in dus).

Kijk voor de duidelijkheid op www.dishpointer.com voor precieze uitrichting van je schoteltje. Een schotel met elevatie-gradenboog op de achterkant is ook gemakkelijk om de beginpositie te vinden.

Als je de ontvanger aanzet met een waterfall display dan zie je bij een juiste uitrichting allemaal signalen opdoemen rond 432,750 MHz. Je zult merken dat de afstelling van de schotel niet ultra-precies is maar als je de RF gain terugdraait dan kun je aan de hand van de S-meter de maximale uitslag zoeken met de schotel.

De signalen zijn zeer goed te nemen, alsof het lokale SSB signalen zijn. En dat op een afstand van 35.786 km !!! Had je niet gedacht he?

Je ziet dat de signalen niet heel ver boven de ruis uit komen maar de S/R ratio is prima. De LNB versterkt ook ruis en alleen een grotere schotel maakt het signaal nog schoner. Maar dat levert geen beter signaal op, dit is namelijk al prima.

Luisteren!

Nu kun je met de ontvanger over de hele band draaien, van 432,500 MHz tot 433,000 MHz. Je hoort onderin CW en in het midden de SSB signalen volgens onderstaand bandplan:

Onderstaand een plot van de dekking van de satelliet:

 

 

 

 

Welcome To Solar Cycle 25; Our Sun Enters A New 11-Year Period

Most of us perceive time as an arrow, a one-way trip into the future. And while that’s true, nature has a way of interpolating circular patterns onto that linear model — day follows night, the seasons progress through the year, and generations are born, live, and die after creating the next generation to do experience the same cycles in the future.

Our star, too, follows this cyclical model, and goes through observable, periodic changes that are of keen interest to solar scientists. So it was with some fanfare that they recently announced that the sun had transitioned into Solar Cycle 25. But what exactly does that mean? Does the Sun’s changing face make much difference to the average person’s daily life? History shows that it can, so it pays to know what we’re in store for over the next couple of decades. Welcome to your primer on Solar Cycle 25.

 

It Goes to Eleven

For as long as scientists have had the ability to (safely) observe the Sun, they’ve noticed that our star is not the perfect glowing orb it at first appears to be. Galileo was among the first to observe that the Sun was marked by small dark imperfections. Observers began to keep track of these sunspots, noting not only their variable number but the fact that they migrate across the Sun’s surface with time.

It would take almost two and a half centuries for anyone to notice that the periodic nature of the patterns of sunspots. German scientist Samuel Heinrich Schwabe is credited with the discovery of the solar cycle in 1843 after 17 years of observations of the average number of sunspots. Swiss scientists Rudolf Wolf used the observations of Schwabe and others to backtrack through the data back to 1755. For solar science purposes, this was designated the year that Solar Cycle 1 started.

Cycles of sunspots for the last 400 years. The earliest data is estimated from geological and tree-ring records. By Robert A. Rohde, CC BY-SA 3.0

The cycle these pioneering solar scientists had discovered has a remarkably regular eleven-year period. The range of variation is very tight, from the nine-year period of Solar Cycle 2 (1766 to 1775) to almost fourteen years for Solar Cycle 4 (1784 to 1798). Each solar cycle is reckoned from a solar minimum, essentially when the sunspot number reaches its local low. The number of sunspots increases over the first half of the cycle, peaking at the solar maximum point before turning down again to head for the next solar minimum.

The raw number of sunspots is not the only interesting cycle the Sun displays. The distribution of sunspots across the Sun’s surface also changes periodically with the solar cycle. At the beginning of each solar cycle, what few sunspots there are tend to cluster at the Sun’s equator. As the cycle progresses and the Sun becomes more active, the sunspots tend to pop up further away from the equator, generally clustering around the mid-latitudes around 30° north and south. As solar maximum passes, sunspots again migrate back to the equator to start the cycle again.

Flipping Magnetic Poles

The periodic changes in the number and distribution of sunspots may be an interesting observation, but what does it mean here on Earth? To help understand that, it pays to recall that despite their dark appearance, sunspots are only marginally cooler than the surrounding solar material. Sunspots are still extremely energetic areas, and as the number of sunspots increases, the output of the Sun (in terms of luminosity) increases.

Sunspots represent places where concentrated lines of magnetic force emerge from deep within the Sun’s interior. Thus a change in the number and location of sunspots reveals changes in the magnetic field of the Sun. It turns out that what’s behind the solar cycle is these periodic changes in the Sun’s magnetic field. (It’s important to note here that the eleven-year cycle is technically the “sunspot cycle,” and the 22-year pole-flipping cycle is the true “solar cycle,” but it’s common practice to use “Solar Cycle” for both.)

The magnetic poles of the Sun are constantly in motion, with the north and south poles flipping every eleven years. At solar minimum, the magnetic poles are roughly aligned with the Sun’s orbital axis, and magnetic lines of force tend to penetrate the photosphere near the equator. As the poles rotate towards the equator, magnetic activity picks up, magnetic lines of force move to high latitudes, increasing the number of sunspots there. The process continues for the back half of the solar cycle as the poles complete their reversal.

So, as each solar cycle progresses due to the migration of the Sun’s magnetic field, solar output increases. Fractional though these changes are, they have obvious implications for life on Earth. But the increasing brightness of our Sun is far from the only impact felt here. The changing magnetic field of the Sun can also have a huge impact on our planet.

What Happens Next?

It’s well known that increased sunspots are associated with stronger and more frequent coronal mass ejections, or CMEs. These events, sometimes energetic in the extreme, occur when magnetic domains in the Sun become so twisted and contorted that they erupt outward, picking up gigatons of highly excited plasma from the Sun’s corona. If the CME occurs in just the right spot on the Sun’s surface, the violently ejected tangle of magnetic flux and plasma can strike the Earth, causing anything from an increase in auroral displays to the catastrophic destruction of infrastructure.

While destructive CMEs are more likely to occur during solar maxima — the 1859 Carrington Event occured near the peak of Solar Cycle 10, and the 1989 Hydro-Québec disaster was about seven months before the peak of Solar Cycle 22 — it’s far from a rule that they only occur then. Plenty of damaging or potentially dangerous CMEs have occurred during solar minima. But the number of CMEs goes up dramatically with the sunspot number, so that the Sun launches a few large outbursts each day during a solar maximum. Simply increasing the number of shots increases the chances of a devasting strike.

While the increased risk of Earth-striking CMEs during solar maximum is a concern, it’s important to keep in mind a few things. First, solar maximum is still about five years away; NASA says that Solar Cycle 25 officially began in December of 2019, meaning we’re still very much in solar minimum conditions. Second, not all solar cycles are created equal. Layered on top of the eleven-year solar cycle are other periodic cycles that we’re only beginning to understand. One is the Gleissberg Cycle, an 87-ish-year cycle where the solar maxima of the eleven-year cycle tend to increase and decrease. We’re currently in the decreasing phase of the Gleissberg Cycle, meaning that the just-completed Solar Cycle 24 had a much lower solar maximum than the previous cycle. The current prediction is that Solar Cycle 25 will be about the same intensity as the previous cycle at solar maximum, and will reach solar maximum around July of 2025.

Source: Space Weather Prediction Center-NOAA

The potential for a sleepy sun for the next eleven years is a “good news, bad news” thing. On the plus side, there’s a greatly reduced — but far from zero — risk of experiencing a catastrophic Earth-striking CME. That means less risk to our vulnerable infrastructure, both terrestrial in terms of the millions of miles of power and communications wires we’ve stitched together, and space-based, since satellites can be greatly impacted by space weather. On the other hand, amateur radio operators and others who depend on ionospheric skip for long-range radio communications, like marine operators, airlines, and the military, always get grumpy when the sun is less active, since fewer sunspots mean decreased ionization of Earth’s atmosphere.

In the end, the Sun is going to do what it does, regardless of how it impacts life here on Earth. All we can do is learn everything possible about the star at the center of our solar system, build good models to predict its behavior over time, and build systems that can withstand our star’s mood swings.

P

Tracking Down Radio Frequency Noise Source, With Help From Mother Nature

Amateur radio operators and shortwave listeners have a common enemy: QRM, which is ham-speak for radio frequency interference caused by man-made sources. Indiscriminate, often broadband in nature, and annoying as hell, QRM spews forth from all kinds of sources, and can be difficult to locate and fix.

But [Emilio Ruiz], an operator from Mexico, got a little help from Mother Nature recently in his quest to lower his noise floor. Having suffered from a really annoying blast of RFI across wide swaths of the radio spectrum for months, a summer thunderstorm delivered a blessing in disguise: a power outage. Hooking his rig up to a battery — all good operators are ready to switch to battery power at a moment’s notice — he was greeted by blessed relief from all that noise. Whatever had caused the problem was obviously now offline.

Rather than waste the quiet time on searching down the culprit, [Emilio] worked the bands until the power returned, and with it the noise. He killed the main breaker in the house and found that the noise abated, leading him on a search of the premises with a portable shortwave receiver. The culprit? Unsurprisingly, it was a cheap laptop power supply. [Emilio] found that the switch-mode brick was spewing RFI over a 200-meter radius; a dissection revealed that the “ferrite beads” intended to suppress RFI emissions were in fact just molded plastic fakes, and that the cord they supposedly protected was completely unshielded.

We applaud [Emilio]’s sleuthing for the inspiration it gives to hunt down our own noise-floor raising sources. It kind of reminds us of a similar effort by [Josh (KI6NAZ)] a while back.

Repeater ISS actief én gewerkt!

Sinds kort is in het International Space Station een transponder actief waarmee je in FM flinke afstanden kunt overbruggen. Kijk maar eens op Amsat voor info hieromtrent.

Op maandag 21 september begon er weer een cyclus met zichtbare overkomsten van het ISS en Thijs, PE1RLN besloot om de gok te wagen om na APRS ook een gewoon QSO te voeren. En met succes! Om 22.30 uur kwam het ISS over en al snel was er communicatie te horen. Thijs gaf een CQ en een Duits tegenstation kwam retour en maakte zo het QSO compleet.

Helaas was de verbinding kort en was Thijs verrast door de snelheid dus heeft hij geen callsign genoteerd…

Op 22 september werd het experiment herhaald bij een lage overgang. Door de afstand waren andere stations sterker en was een verbinding niet mogelijk. Maar anderhalf uur later kwam het ISS recht boven Hulsberg en werd er een eerste compleet QSO gemaakt! Luister hier naar het fragment van een nagenoeg kristalheldere verbinding:

Audio

Super cool natuurlijk en nu is bij Thijs het hek van de dam…

Luister mee op 437.800 MHz +/- doppler van maximaal 15kc. Of op de ingang op 145.990 MHz.

 

 

Op de foto de QRPeater die de richtantenne bedient

Just Who Makes Tubes These Days?

For most of us, electronic technology comes in the form of solid state devices. Transistors, integrated circuits, microcontrollers. But for the first sixty years or so of the field existing, these devices either hadn’t been invented yet or were at too early a stage in their development to be either cost-effective, or of much use. Instead a very different type of electronic component ruled the roost, the vaccum tube.

A set of electrodes in an evacuated glass envelope whose electrical properties depended on the modulation of the flow of electrons through them, these were ubiquitous in consumer electronics up until the 1960s, and clung on in a few mass-market applications even as far as the mid 1970s. As cheaper and more versatile semiconductors superseded them they faded from electronic parts catalogues, and the industry that had once produced them in such numbers disappeared in favour of plants producing the new devices. Consumer products no longer contained them, and entire generations of engineers grew up never having worked with them at all. If you were building a tube amplifier in the early 1990s, you were a significant outlier.

Alive And Kicking In The 21st Century

The warm glow of a tube amplifier lends credibility to an audiophile set-up. Hannes Grobe / CC BY-SA 4.0
The warm glow of a tube amplifier lends credibility to an audiophile set-up. Hannes Grobe / CC BY-SA 4.0.

As our consumer electronics have become ever more digital in their make-up, interest has blossomed in analogue devices, or at least devices with a visibly analogue component. In particular the world of audio has begun to chase the elusive “tube sound”, whether it be in the context of intentionally overdriven amplifiers for the guitarist, or closer to perfect ones for the audiophile.

High-end hi-fi shops are full of tube-based devices, and a plethora of tube amplifier kits are available for the electronics enthusiast. Tubes can be bought under a bewildering array of brands often at eye-watering prices, something of a surprise for a technology which might be presumed to have disappeared over four decades ago. This does raise an interesting question though, with such a large number of tube brands on the market, where are they all made, and how have their manufacturers survived for so long? The answer is relatively straightforward, yet in other aspects a story of labyrinthine complexity.

High-power transmitting tubes never went away. Angeloleithold (CC BY-SA 3.0)
High-power transmitting tubes never went away. Angeloleithold (CC BY-SA 3.0)

While consumer vacuum tubes might have disappeared from mundane electronics decades ago, it’s first worth pointing out that many of the old names in the vacuum tube business didn’t stop manufacturing vacuum tubes, they simply stopped making the tubes you might be familiar with. There are industrial applications in which vacuum devices are very much still with us , even though in many cases they have semiconductors snapping at their heels.

High power RF amplifiers for UHF and higher frequencies for example still use vacuum tubes, be they specialised planar tubes or slightly more exotic fare such as klystrons. Similarly there are specialised RF applications that still use travelling wave tubes, and very high power industrial equipment that uses vacuum and gas-filled tubes for control or rectification.

But who is making the “normal” tubes — the smaller glass-envelope tubes, small triodes and pentodes such as you’d find in that guitar amplifier? We recognize some names from times past such as Telefunken or Mullard, others are modern brands such as JJ or Fender’s Groove Tubes brand, and others are clearly Russian or Chinese names such as Svetlana, SovTek, “Winged C“, or Shuguang. Clearly there are not as many tube factories left in the world as there are logos stamped on the glass of imported tubes, so what on earth is going on?

A Technology For The Few, Not The Many Any More

The answer is that the consumer tube business in 2020 is no longer a commodity component market producing the lifeblood of a million televisions and radios, instead it’s a boutique operation serving a niche market. Looking at the tubes available, it’s clear that if you are searching for an obscure 1050s small-signal RF tube you’ll be out of luck; these are mostly audio amplifier parts, double triodes, output pentodes, even the occasional power rectifier, and at costs that would raise an eyebrow or two for buyers of their originals.

A current-manufacture Mullard-branded ECC83 (12AX7) general purpose small signal double triode for example costs $43.20 (£35.09) in 2020, while browsing a 1957 copy of Wireless World we find the same part number advertised for 8 shillings and thruppence, which is £0.41 ($0.51) in post-decimalisation British money. Using the Bank of England’s inflation calculator that comes out at about £9.96 ($12.27) today, so the modern re-issue is more than three times as expensive as was the genuine article in its heyday. This is evidently a business with a significant mark-up, and the world’s remaining tube factories are cashing in.

A selection of Mullard ECC83s from back in the day.
A selection of Mullard ECC83s from back in the day.

Investigating further, we find that tube manufacture of this type appears to be entirely absent from the Americas and Western Europe. It survived the decline of the 1970s in Russia, China, and the formerly Communist states of eastern Europe, and as Soviet communism fell and the Chinese economy grew in the 1990s it emerged from the shadows to supply the audio market. These count among them factories that have been in the tube business for a very long time indeed, and their products have many proven decades of reliable service.

So if you buy a tube with a Western sounding brand name today it will have been made in the same Eastern factories as those with an obviously Communist heritage, and thus given that the same part numbers are available from the same sources under those cheaper brands it’s difficult not to wonder whether or not they are in fact exactly the same tubes but with an inflated price.

Communism, Folks, The Secret To High-End Audio

JJ’s take on the KT88 power beam pentode.

In the Slovak Republic are JJ, a very long-established tube manufacturer who were previously the consumer end of the Tesla vacuum device range. They don’t admit to branding their tubes for anyone else on their website, but they are reputed to be the source of those Telefunken-branded parts. Moving eastwards to Russia we then find SED-SPb in St. Petersburg, for whom consumer tubes are listed on the website as a small part of their range alongside industrial and high-power RF vacuum devices. They were previously the producers of the Svetlana range of tubes through the Soviet era, and though they no longer have that brand name they retain the winged C logo from that era. It’s unclear whether they are still involved in the production of branded tubes as their website is not very informative, but the “Winged C” tubes manufactured by them are still on sale.

Further across Russia in the southern Russian city of Saratov is the Expo-PUL factory, and here is where the story becomes interesting. It’s owned by the American Electro-Harmonix company, who in turn hold the rights for a host of older brands including Svetlana, Sovtec, Mullard, and Tung-Sol. It’s here that reissued Mullard ECC83 is made, and it has made the news in the past as Russian mobsters reportedly tried to seize it.

PSVane are definitely marketing their tubes such as this 300B as desirable high-end products.
PSVane are definitely marketing their tubes such as this 300B as desirable high-end products.

Into China, and the situation becomes rather opaque. China has a selection of larger manufacturers who produce tubes to a very high quality for the high-end export trade, but there are also inexpensive tubes on the market with scant manufacturer logos and little else in the way of traceability. If you pay $20 for an AliExpress tube headphone amplifier kit then it’s likely you’ll receive one of this latter variety, but its origins will be unclear.

The largest Chinese manufacturer is ShuGuang, based in Changsha, in Hunan province. They manufacture a large range as well as producing components for other brands. Their upstart competitor PSVane is also based in Changsha, and concentrates specifically on the high-end audio market. It’s unlikely for example that a 45 cent 6j1 small-signal pentode will have come from either of these two manufacturers or their smaller high-end competitors though, so it’s clear that there are more Chinese tube manufacturers at all levels of the market than can easily be found from the other side of the world.

Is It Really Worth It Though?

As someone who has been a vacuum technology enthusiast for four decades now it makes me happy to find that tubes are still in production and their industry appears healthy for now. But my tour through the world of 21st century tube manufacture leaves me slightly disappointed that so much of their marketing is still clouded by mythology.

As someone who was building tube amplifiers with Yugoslavian TV tubes back when it was extremely unfashionable, I understand the allure of that elusive “tube sound”, but experience has taught me that it’s not as great a thing as its proponents would have you believe. Even the distortion characteristics sought by musicians can more easily  be created through DSP in 2020, so I can’t help the feeling that people are being led astray as I see essentially the same tube being sold at a range of different prices based solely on its brand. Enjoy working with tubes, and enjoy listening to a tube amplifier. But don’t make the mistake of falling into the trap of falling for the hype, and never lose sight of the engineering.

Modern Radio Receiver Architecture: From Regenerative To Direct Conversion

Modern radio receivers have a distinct advantage over the common early designs which I covered in my previous article. Most of the receivers you will have worked with over the past couple decades are designs by Edwin Armstrong; regenerative, superregenerative, or most commonly superheterodyne. These are distinguished by a few fascinating key traits that bring both benefits and drawbacks.

Today let’s dive into Mr. Armstrong’s receivers. I’ll also talk about DC receivers which, despite the name, are not made to listen to batteries. These are receivers you are much more likely to encounter in modern equipment.

Regenerative and Superregenerative

The regenerative receiver is all about doing more with less. You still see some of these in simple applications like RF remote controls. The idea derives from how an oscillator works. In a simple way of thinking, an oscillator is an amplifier with enough positive feedback that any tiny signal at the right frequency will amplify and then, through feedback, continue to output over and over. If everything were perfect, then, an oscillator would have infinite gain at a given frequency.

Of course, things aren’t perfect, but they are close enough. You have to set the feedback network up just right to get the frequency you want. Also, things in nature tend to be linear, so it isn’t like the amplifier has no gain at the given frequency and then suddenly has infinite gain. The gain increases until it meets the Barkhausen criteria and achieves stable oscillation.

In fact, sometimes we want to build an amplifier and find that it oscillates for some reason. Maybe that’s what made Edwin Armstrong think about the regenerative receiver. In it, an amplifier is pushed almost to the point of oscillation at the frequency of interest. This can result in a huge gain for a single tube or transistor. This was especially important when using low-quality active devices. For example, a tube capable of a gain of 10 without regeneration might amplify between 5,000 and 10,000 times when it was right on the edge of oscillation.

That’s a big improvement and meant that a very simple device could pick up very distant radio signals. There are many ways you could arrange positive feedback. However, the most common way (as in the accompanying schematic) was to have a pickup coil called a tickler around the primary tuned circuit coil. If that coil was out of phase, you’d get negative feedback, so common advice on this kind of radio was that if it didn’t work after you built it, try reversing the leads of the tickler.

The superregenerative was another design by Armstrong. It is essentially the same circuit, but after a certain frequency higher than the bandwidth of interest, the design stops the oscillation action allowing it to build again. Armstrong called this quenching. This could improve gains into the neighborhood of a million times. Armstrong’s original demonstration of the concept showed a three-tube receiver that was as sensitive as a nine-tube conventional design.

There are some downsides to both of these designs, though. You usually have to adjust the regeneration and the circuit can easily go into oscillation, producing a squeal. It also radiates signal back out the antenna, so it is a sort of transmitter. This is bad for interference or — for military applications — where you wish not to be found. If you want to build your own, we’ve had some advice for you in the past, including some on a breadboard. If you prefer, you can just simulate one that [Qrp Gaijin] demonstrates in the video below.

Superheterodyne

Armstrong was also behind the most successful architecture of all, the superheterodyne. If you have a non-software defined radio, it probably uses this technique. The idea is simple and has to do with selectivity. Consider the TRF radio. You can get better performance by putting more stages ahead of the detector. But each stage has to cover the entire range of the radio and requires tuning when you change frequency.

Armstrong’s idea was to limit that. You may or may not have one relatively broad filter in front of a mixer that adds (and subtracts) two RF signals. Then a local oscillator provides another signal to the mixer. Suppose you want to receive a signal at 1 MHz and you set the local oscillator to 9 MHz. You’ll get a signal at 10 MHz (and 8 MHz). You can now filter that 10 Mhz signal and amplify it using filters and amplifiers that you don’t have to tune (at least, not more than once). This makes their design simple and is also less hassle for the operator.

Now, if you want to receive a signal at 1.1 MHz, you change the local oscillator to 8.9 MHz. You still get a 10 MHz signal. If there is a station at 1.2 MHz, you’ll also get a signal at 10.1 MHz, but since you have the 10 MHz filters and amplifiers, you can get rid of that easily. That 10 MHz, in this example, is the IF or intermediate frequency.

This is a great way to build a radio. You can pile on gain and selectivity by adding more IF stages. The only real downside, as I mentioned in the last article is the possibility of images. Because the mixer both adds and subtracts, you can hear a station at the wrong frequency. Consider our 1 MHz signal with a local oscillator frequency of 9 MHz. A 19 MHz signal at the antenna will also show up at the 10 MHz output of the mixer since 19-9=10, just like 1+9=10.

There are several ways to get over that. First, you can filter before the mixer. That’s why a lot of radios have a band switch — well, it is at least one of the reasons. You select a filter that roughly cuts out the interference from images. High-quality receivers will use dual conversion where one mixer produces one IF signal that is later mixed again to form a second one. Some will even use more conversions to optimize filtering.

There are several ways this can help. Image frequencies are always at twice the local oscillator frequency. Going back to the 1 MHz signal example, the image is at 2×9+1=19 MHz. So the higher the IF, the easier it is to filter off images. As a silly example consider if the 1 MHz receiver used an IF of 61 MHz. Now the local oscillator will run at 60 MHz and the image frequency will be at 121 MHz. It is trivial to filter 1 MHz from 121 MHz.

The problem is that using a higher IF makes it more difficult to reject stations adjacent in frequency. In our extreme example, filters to select between 61 MHz and 61.02 MHz are going to be more complex and costly than ones that select between 10 MHz and 10.02 MHz. Granted, there are surface acoustic wave filters and other devices that can do the job, but typically the best performance for a given cost is going to go to the lower frequency filters and amplifiers.

If you want a nice overview of the superheterodyne that isn’t too technical, check out the video below.

Direct Conversion

The direct conversion (DC) receiver has seen a resurgence in use since many software defined radios use this as a front end before digitizing the signal. You can think of a DC receiver as superheterodyne where the local oscillator doesn’t produce an IF, but instead is set to the frequency you want to receive. That means the output is the detected radio signal.

Using our 1 MHz example, to tune it in, you set the local oscillator to 1 MHz. The output is what you’d normally process with an audio amplifier (in the case of AM radio). The design has several practical problems. If the local oscillator isn’t locked to the transmitting station, the output will be incorrect. With SDR, that’s not a problem because the SDR software can track any shifts, but if you don’t have a computer handling things, it requires a lot of components to stay on frequency (essentially, a phase locked loop).

On the other hand, images are all at low frequencies and easily rejected. A lot of simple ham radio receivers use this technique because you don’t need a lot of frequency-specific amplifiers and filters that require tuning.

Getting Started Receiving

If you want to start designing receivers, the best bet is to build some and see how they work. It is hard to beat the simplicity and performance of a regenerative receiver. Sure, a crystal set is easier, but it won’t pick up like a regen. Using the NE602 or NE612 mixer is a handy way to make a direct conversion receiver with only a little more work. You can use that same mixer in a superhet design, but it is definitely more work.

Even if you are using SDR, you usually need some kind of front end. There are a few more exotic designs we didn’t talk about. If you want to read about Hartley, Barber Weaver, and other interesting topics, A Texas A&M presentation on the topic will fill you in.

Of course, the best way to learn is to go build something! There’s no shortage of design ideas for every kind of radio we’ve discussed. Once you start tweaking on real hardware, you’ll quickly find out what works and what doesn’t.

Acknowledgment: Most of the pretty pictures of block diagrams and schematics were adapted from public domain sources on Wikipedia, particularly from [Chetvorno]. What a great resource.

Dipole Antenna Is Off Balance

A dipole antenna is easy, right? Two wires, each a quarter wavelength long, emanate from a coax or other feedline. Unless it is an off-center dipole. The length is still the same, but you move the feed point to a different part. [KB9VBR] explains how this changes the antenna’s impedance from the nominal 70 ohms of a standard dipole.

Why would you want to do that? The trick is to find a feed point that has acceptable impedance on multiple ham radio bands. Most automatic tuners can handle a certain range of mismatch so using an antenna like this with a tuner can allow one antenna to serve multiple bands with no traps or switches.

[KB9VBR] uses a 4:1 balun to convert the relatively high impedance to something close enough for a tuner to work with. A cordless soldering iron comes in handy for antenna work and in the video you can see a gas-powered iron making short work of the connections to the 14 gauge wire.

The impedance also depends on height and he suggests 30 feet, at least. Does it work? If you watch the end of the video, it apparently does. If you are in the mood for technical talk about ham antennas, you could do worse than watch this MIT video. If you want a novel take on why antennas work, you might want to read about the kink.

Hemelvaart-velddag succesvol!

Op Hemelvaartsdag 21 mei hield de Velddag Crew Zuid-Limburg een kleine velddag in Epen. Het beloofde prachtig en warm weer te worden dus ideaal om te propagatie deze dagen eens onder de loep te nemen. Met ruim 1,5m onderlinge afstand en een zeer kleine bezetting werd voldaan aan de veiligheidsinstructies van de lokale overheid.

Donderdag

Het begon al snel warm te worden en rond 12u werden de eerste verbindingen binnen Europa gemaakt. In het ruisvrije buitengebied zaten de 80m, 40m en 20m banden propvol stations maar dat waren hoofdzakelijk Duitse en Italiaanse amateurs, niet spectaculair. De hele middag blijft het bij knalharde stations en werken we wat Engelsen, Schotten en Scandinavische stations.

Daar dient zich om half 6 het eerste DX station aan: W0AAE uit de VS. Het is vlak voor het avondeten en na slechts 1 keer aanroepen komt hij terug met uitstekende cijfers: 57 over bijna 7.000km. De BBQ worsten smaakten extra goed hierdoor.

PY6RT uit Brazilië meldt zich in de avond. Het koelt langzaam af en daar gaat de band fijn van open. Met ruim 8.000km en 100W in de FD-4 beslist een mooie verbinding om bijna 9 uur. Daarna wordt het rustig op de band en breken we rond 22 uur op.

Vrijdag

De tweede dag begint drukkend en bewolkt, geen goed vooruitzicht. De weersvoorspellingen zijn niet goed voor de namiddag dus er is haast geboden.

KC1KUG is er vroeg bij om 12 uur. Prima rapport en gewerkt door 3 stations op de velddag en goed voor 5.630km.

Hierna wordt het weer minder en begint het te waaien. Met onweer in het vooruitzicht wordt besloten om rond 4 uur op te breken en nog even wat te eten alvorens te gaan.

W4IPC meldt zich met 6.447km op de valreep, prima signaal 57/58. Blijkbaar is er dus toch conditie met dit weer mogelijk.

Conclusie

Jammer genoeg was overnachten geen optie, anders hadden we donderdag nacht kunnen ervaren of de temperatuur inversie voor nog betere condities zorgt. Met het signaal uit Brazilië op 14MHz waren de voortekenen goed, zeker op lagere frequenties. Helaas werd vrijdag niet zo mooi als donderdag, al begonnen de condities op vrijdag al vroeger en had het nog interessant kunnen worden…

Al met al een geslaagde tweetal dagen, dit jaar weer eens in eigen land. Noodgedwongen door de corona-maatregelen in kleine bezetting (6 OM’s) en zonder kennisgeving vooraf om bezoek te voorkomen. Laten we hopen dat we deze velddag nog eens over kunnen doen onder betere omstandigheden. Voor nu geldt: missie geslaagd, gegeven de omstandigheden.

73!

Velddag Team Zuid-Limburg