When you think of a software defined radio (SDR) setup, maybe
you imagine an IC or two, maybe feeding a computer. You probably don’t
think of a vacuum tube. [Mirko Pavleski] built a one-tube shortwave SDR
using some instructions from [Burkhard Kainka] which are in German, but Google Translate is good enough if you want to duplicate his feat. You can see a video of [Mirko’s] creation, below.
The build was an experiment to see if a tube receiver could be stable
enough to receive digital shortwave radio broadcasts. To avoid AC line
hum, the radio is battery operated and while the original uses an EL95
tube, [Mirko] used an EF80.
To get the necessary stability, it is important that everything is
secured. The original build made sure the tube would not move during
operation, although [Mirko’s] tube mounting looks more conventional but
still quite secure. Loose coupling of the antenna also contributes to
stability, and the tuning adjustments ought to have longer shafts to
minimize hand capacitance near the tuning knob. Another builder [Karl
Schwab] notes that only about 1/3 of the tuning range is usable, so a
reduction gear on the capacitor would also be welcome.
The tube acts as both an oscillator and mixer, so the receiver is a
type of direct conversion receiver. The tube’s filament draws about 200
mA, so battery operation is feasible.
According to [Burkhard] his build drifts less than 1 Hz per minute,
which isn’t bad. As you can see in the video, it works well enough. The
EF80, by the way, is essentially an EF50
with a different base — that tube helped win World War II. If you like
to build everything, maybe you could try the same feat with a homemade tube.
De bovenregionale repeater PI2NOS wordt ontmanteld. Dat meldt de Stichting Scoop Hobbyfonds op
haar website. Vorige week stopte de ontvanger in Breda. De komende
weken volgen een aantal locaties in het noorden van het land.
De stichting noemt drie redenen waarom PI2NOS in zijn huidige vorm moet stoppen.
De eerste en belangrijkste reden is dat de
inkomsten van sponsoren en donateurs teruglopen. Ten tweede heeft de
bovenregionale repeater al lange tijd te kampen met frequentiemisbruik.
Sommige mensen verstoren het verkeer op de PI2NOS zodanig dat
goedwillenden afscheid nemen van de repeater. Ondanks extra inspanningen van het Agentschap Telecom
zijn de verstoringen niet gestopt. Tot slot noemt de stichting als
reden dat de kosten van de verschillende opstellocaties voor hun
Het is jammer dat dit unieke project van gekoppelde radiosystemen in zijn huidige vorm niet kan blijven bestaan.
From today’s perspective, vacuum tubes are pretty low tech.
But for a while they were the pinnacle of high tech, and heavy research
followed the promise shown by early vacuum tubes in transmission and
computing. Indeed, as time progressed, tubes became very sophisticated
and difficult to manufacture. After all, they were as ubiquitous as ICs
are today, so it is hardly surprising that they got a lot of R&D.
Prior to 1938, for example, tubes were built as if they were light
bulbs. As the demands on them grew more sophisticated, the traditional
light bulb design wasn’t sufficient. For one, the wire leads’ parasitic
inductance and capacitance would limit the use of the tube in
high-frequency applications. Even the time it took electrons to get from
one part of the tube to another was a bottleneck.
There were several attempts to speed tubes up, including RCA’s acorn tubes, lighthouse tubes,
and Telefunken’s Stahlröhre designs. These generally tried to keep
leads short and tubes small. The Philips company started attacking the
problem in 1934 because they were anticipating demand for television
receivers that would operate at higher frequencies.
Dr. Hans Jonker was the primary developer of the proposed solution
and published his design in an internal technical note describing an
all-glass tube that was easier to manufacture than other solutions. Now
all they needed was an actual application. While they initially thought
the killer app would be television, the E50 would end up helping the
Allies win the war.
Britain, there was a single television transmitter at Alexandra Palace —
the start of what would become the BBC. This was not only the first
public television service but also the first fully electronic television
system. Pye Ltd. — a company eventually bought by Philips — made
receivers that were surprisingly successful. The sound was at 41.5 Mhz
and the visual was at 45 MHz — high frequencies for those days.
Spurred by the demand, Pye decided that a set with more range would
create a broader market for receivers. The problem was finding a tube
that could handle the 45 MHz frequency in their tuned radio frequency
Pye wrote out the specifications for what they needed, but couldn’t
get them made reliably and cheaply. They turned to Philips who took
Jonker’s ideas and added some items needed for this application,
producing the EF50 — a pentode. The resulting TV set (see page 199) had a range of about five times the older sets.
Old tubes used a difficult process called pinching to seal the end of
a glass tube with the leads running through it. The pinch formed an
inverted V shape where the bakelite base of the tube fit the wide part
of the V and the wires within entered the tube through the point of the
had several problems. As more wires had to pass through the pinch, they
had to get closer together. That increased stray capacitance. Worse,
the distance from the bottom of the V to the top of the V meant wires
had to be relatively long which added inductance. Finally, the size of
the V — often half the total length of the tube — was preventing tubes
from getting smaller, hindering the development of portable equipment.
One way to solve this was to build the tubes from metal instead of
glass, with some connections going through the top of the tube. However,
these tubes were expensive to manufacture in quantity and designers did
not like having to wire to the top of the tube. The Stahlröhre bucked
the trend, putting the tube components in horizontally to decrease
wiring to the base and using no top connections. However, again, the
cost to manufacture was high. The 1934 acorn tube was all glass and used
two parts sealed together with short leads but were also known to be
expensive to produce.
Philips, Pye, and the War
When the Dutch military first asked Philips for tubes around 1918,
they declined; Gerard Philips though radio had little practical value.
It would be 1923 before Philips decided to use its expertise in light
bulbs to produce radio tubes. By 1938, Jonker’s work was circulating and
in 1939 there was even an article about it in Wireless Engineer.
By the time Pye came looking for high-frequency tubes, Philips was
ready due to the earlier work. The Pye receiver used six tubes and
required some tweaking, including the addition of a metal shield.
Meanwhile, there was war. The Battle of Britain was in 1940 and the
military was busy in 1939 working on RADAR that also operated at high
frequencies. This RADAR — and the command and control strategies used
with it — would be key to winning the upcoming battle. The team working
on airborne RADAR apparently only had one receiver good enough to get
results. Then they received a tip that Pye had an excellent receiver
that worked in the same frequency range. This became the basis for
Britain’s RADAR sets through the war. About 60% of all Pye TV IF strips
wound up in British RADAR sets.
The big problem was that by 1940 the Netherlands was in German hands.
The production line needed to be moved to Britain, and when the HMS
Windsor took the escaping Dutch government to England, the Philips
family was also onboard with the diamond dies needed to produce the fine
tungsten wires used in the EF50 tube.
After the war, the EF50 would find a home in many oscilloscopes and
radio receivers. This was both because of its superior frequency ability
and the availability of war surplus. Others would also produce the tube
including Marconi-Osram (as the Z90) and Cossor (63SPT). Mullard
produced the tube using the original Phillips equipment and both Rogers
and Sylvania also produced a version.
type of tube would be the king of the hill for RF work until 1959.
That’s the year RCA introduced the nuvistor — a metal and ceramic tube
assembled in a vacuum chamber. These were nearly as tiny as a
transistor, low noise, and had excellent performance at radio
frequencies. These were found in a lot of gear all the way until the
early 1970s including TV tuners, oscilloscopes, and tape recorders.
If you like the sound of an old tube radio, the medium wave receiver
in the video below uses some EF50s and it sounds great. Want more tube history? Or perhaps you’d rather make your own. Or you can watch how they made similar tubes back in the day.
Using the DMYCO V8 Finder, [Corrosive] demonstrates how to set up the
device to pick up terrestrial amateur streams. Satellite reception
typically involves the use of a low-noise block downconverter, which
downconverts the high frequency satellite signal into a lower
intermediate frequency. Operating at the 1.2GHz amateur band, this isn’t
necessary, so the device is configured to use an LNB frequency of
10000, and the channel frequency entered as a multiple of ten higher. In
this case, [Corrosive] is tuning in an amateur channel on 1254 MHz,
which is entered as 11254 MHz to account for the absent LNB.
[Corrosive] points out that, when using an F-connector to BNC adapter
with this setup, it’s important to choose one that does not short the
center pin to the shield, as this will damage the unit. This is due to
it being designed to power LNBs through the F-connector for satellite
By simply reconfiguring a satellite finder with a basic scanner
antenna, it’s possible to create a useful amateur television receiver.
If you’re wondering how to transmit, [Corrosive] has that covered, too. Video after the break.
There was a time — not long ago — when radio and even wired
communications depended solely upon Morse code with OOK (on off keying).
Modulating RF signals led to practical commercial radio stations and
even modern cell phones. Although there are many ways to modulate an RF
carrier with voice AM or amplitude modulation is the oldest method. A recent video
from [W2AEW] shows how this works and also how AM can be made more
efficient by stripping the carrier and one sideband using SSB or single
sideband modulation. You can see the video, below.
As is typical of a [W2AEW] video, there’s more than just theory. An
Icom transmitter provides signals in the 40 meter band to demonstrate
the real world case. There’s discussion about how to measure peak
envelope power (PEP) and comparison to average power and other
measurements, as well.
Although the examples use a ham radio band, the concepts will apply
to any radio frequency from DC to light. If you want to do similar
measurements, you’d need a scope, a peak-reading watt meter, and a dummy
load along with the transmitter.
We enjoyed that he uses a scope probe as a pointer, but we can’t really explain why. If you are ambitious, you can build your own SSB transceiver. Another common way to modulate RF is FM and we’ve talked about it before, too.
Who doesn’t like to look up at the night sky? But if you are
into radio, there’s a whole different way to look using radio
telescopes. [John Makous] spoke at the GNU Radio Conference about how
he’s worked to make a radio telescope that is practical for even younger students to build and operate.
The only real high tech part of this build is the low noise amplifier
(LNA) and the project is in reach of a typical teacher who might not be
an expert on electronics. It uses things like paint thinner cans and
lumber. [John] also built some blocks in GNU Radio that made it easy for
other teachers to process the data from a telescope. As he put it,
“This is the kind of nerdy stuff I like to do.” We can relate.
The telescope is made to pick up the 21 cm band to detect neutral
hydrogen from the Milky Way. It can map the hydrogen in the galaxy and
also measure the rotational speed of the galaxy using Doppler shift. Not
bad for an upcycled paint thinner can. These are cheap enough, you can
even build a fleet of them.
This would be a great project for anyone interested in radio
telescopes or space. However, it is particularly set up for classroom
use. Students can flex their skills in math, engineering, programming,
and — of course — astronomy and physics.
The general public thinks there is one thing called a radio.
Sure, they know there are radios that pick up different channels, but
other than that, one radio is pretty much like the other. But if you are
involved in electronics, you probably know there are lots of ways a
radio can work internally. A crystal set is very different from an FM
stereo, and that’s different still from a communications receiver. We’d
say there are several common architectures for receivers and one of the
most common is the superheterodyne. But what does that mean exactly?
[Technology Connection] has a casual explanation video that discusses how a superhet works and why it is important. You can see the video, below.
Engineering has always been about building on abstractions. This is
especially true now when you can get an IC or module that does most of
what you want it to do. But even without those, you would hardly start
an electronics project by mining copper wire, refining it, and drawing
your own wire. You probably don’t make many of your own resistors and
capacitors, neither do you start your design at the fundamental
electronic equations. But there’s one abstraction we often forget about:
architecture. If you are designing a receiver, you probably don’t try
to solve the problem of radio reception; instead you pick an
architecture that is proven and design to that.
There are other examples. Do you really work out a binary counter
every time? Or how to make an op-amp amplify? You start with those
building blocks. Of course, true innovation means you have to stop doing
that and actually think of new and different (and possibly better) ways
to do the same task. But most of the time you aren’t trying to
innovate, you are trying to get the job done.
The video is pretty straightforward and doesn’t assume you have much
radio background. However, it does manage to do some real demonstrations
and it is worth a watch. There are many other receiver architectures,
of course. Regenerative,
superregenerative, homodyne (direct conversion), Hilbert, and Weaver
are all types of receivers and there are doubtless more. The funny part
is that many of the ideas we still use today came from one man: Edwin Armstrong.