There used to be a time when amateur radio was a fairly
static pursuit. There was a lot of fascination to be had with building
radios, but what you did with them remained constant year on year. Morse
code was sent by hand with a key, voice was on FM or SSB with a few
old-timers using AM, and you’d hear the warbling tones of RTTY traffic
generated by mechanical teletypes.
By contrast the radio amateur of today lives in a fast-paced world of
ever-evolving digital modes, in which much of the excitement comes in
pushing the boundaries of what is possible when a radio is connected to a
computer. A new contender in one part of the hobby has come our way
from [Guillaume, F4HDK], in the form of his NPR, or New Packet Radio mode.
NPR is intended to bring high bandwidth IP networking to radio
amateurs in the 70 cm band, and it does this rather cleverly with a
modem that contains a single-chip FSK transceiver intended for use in
licence-free ISM band applications. There is an Ethernet module and an
Mbed microcontroller board on a custom PCB, which when assembled
produces a few hundred milliwatts of RF that can be fed to an
off-the-shelf DMR power amplifier.
Each network is configured around a master node intended to use an
omnidirectional antenna, to which individual nodes connect.
Time-division multiplexing is enforced by the master so there should be
no collisions, and this coupled with the relatively wide radio bandwidth
of the ISM transceiver gives the system a high usable data bandwidth.
Whether or not the mode is taken up and becomes a success depends
upon the will of individual radio amateurs. But it does hold the
interesting feature of relying upon relatively inexpensive parts, so the
barrier to entry is lower than it might be otherwise. If you are
wondering where you might have seen [F4HDK] before, we’ve previously
brought you his FPGA computer.
There are a few options if you want to network computers on
amateur radio. There are WiFi hacks of sort, and of course there’s
always packet radio. New Packet Radio,
a project from [f4hdk] that’s now on hackaday.io, is unlike anything
we’ve seen before. It’s a modem that’s ready to go, uses standard 433
ISM band chips, should only cost $80 to build, and it supports
bidirectional IP traffic.
The introductory documentation for this project
(PDF) lays out the use case, protocol, and hardware for NPR. It’s based
on chips designed for the 433MHz ISM band, specifically the SI4463 ISM
band radio from Silicon Labs. Off the shelf amplifiers are used, and the
rest of the modem consists of an Mbed Nucleo and a Wiznet W5500
Ethernet module. There is one single modem type for masters and clients.
The network is designed so that a master serves as a bridge between Hamnet,
a high-speed mesh network that can connect to the wider Internet. This
master connects to up to seven clients simultaneously. Alternatively,
there is a point-to-point configuration that allows two clients to
connect to each other at about 200 kbps.
Being a 434 MHz device, this just isn’t going to fly in the US, but
the relevant chip will work with the 915 MHz ISM band. This is a great
solution to IP over radio, and like a number of popular amateur radio
projects, it started with the hardware hackers first.
In the radio business, getting the high ground is key to
covering as much territory from as few installations as possible.
Anything that has a high profile, from a big municipal water tank to a
roadside billboard to a remote hilltop, will likely be bristling with
antennas, and different services compete for the best spots to locate
their antennas. Amateur radio clubs will be there too, looking for space
to locate their repeaters, which allow hams to use low-power mobile and
handheld radios to make contact over a vastly greater range than they
could otherwise.
Now some hams have claimed the highest of high ground for their
repeater: space. For the first time, an amateur radio repeater has gone
to space aboard a geosynchronous satellite, giving hams the ability to
link up over a third of the globe. It’s a huge development, and while it
takes some effort to use this new space-based radio, it’s a game
changer in the amateur radio community.
Friends in High Places
The new satellite, Es’hail-2,
was built for Es’hailSat, a Qatari telecommunications concern. As
satellites go, it’s a pretty standard machine, built primarily to
provide direct digital TV service to the Middle East and Africa. But
interestingly, it was designed from the start to carry an amateur radio
payload. The request for proposals
(RFP) that Es’hailSat sent to potential vendors in early 2014
specifically called for the inclusion of an amateur repeater, to be
developed jointly by AMSAT, the Radio Amateur Satellite Corporation.
The repeater aboard Es’hail-2 was developed as a joint effort between the Qatar Amateur Radio Society (QARS), Es’HailSat, and AMSAT-DL,
the AMSAT group in Germany. The willingness of Es’HailSat to include an
amateur radio payload on a commercial bird might be partially explained
by the fact that the QARS chairman is His Excellency Abdullah bin Hamad
Al Attiyah (A71AU), former Deputy Prime Minister of Qatar.
The repeater was engineered with two main services in mind. The first
is a narrowband transponder intended for phone (voice) contacts,
continuous wave (CW) for Morse contacts, and some of the narrow
bandwidth digital modes, like PSK-31. The other transponder is for
wideband use, intended to test Digital Amateur Television (DATV). The
wideband transponder can carry two simultaneous HD signals and a beacon
broadcasting video content from QARS. Both transponders uplink on the
portion of the 2.4-GHz reserved for hams, while downlinking on the
10.4-GHz band.
Es’hail-2 was launched aboard a SpaceX Falcon 9 from Cape
Canaveral on November 15, 2018. The satellite was boosted to a
geosynchronous orbit in the crowded slot located at 26.5° East
longitude, parking it directly above the Democratic Republic of Congo.
After tests were completed, a ceremony inaugurating the satellite as
“Qatar OSCAR-100”, or QO-100, was held on February 14, 2019, making it
the 100th OSCAR satellite launched by amateurs.
Listening In
Sadly for hams in the Americas and most of eastern Asia, QO-100 is
out of range. But for hams anywhere from coastal Brazil to Thailand, the
satellite is visible 24 hours a day. The equipment to use it can be a
bit daunting, if the experience of this amateur radio club in Norway
is any indication. They used a 3-meter dish for the 2.4-GHz uplink,
along with a string of homebrew hardware and a lot of determination to
pull off their one contact so far, and this from a team used to bouncing
signals off the Moon.
Receiving signals from QO-100 is considerably easier. A dish in the
60-cm to 1-meter range will suffice, depending on location, with a
decent LNB downconverter. Pretty much any SDR will do for a receiver. An
alternative to assembling the hardware yourself — and the only way to
get in on the fun for the two-thirds of the planet not covered by the
satellite — would be to tune into one of the WebSDR ground stations that
have been set up. The British Amateur Television Club and AMSAT-UK,
located at the Goonhilly Earth Station, have set up an SDR for the narrowband transponder that you can control over the web. I used it to listen in on a number of contacts between hams the other night.
It’s hard to overstate the importance of QO-100. It’s the first ham
repeater in geosynchronous orbit, as well as the first DATV transponder
in space. It’s quite an achievement, and the skills it will allow hams
to develop as they work this bird will inform the design of the next
generation of ham satellites. Hats off to everyone who was involved in
getting QO-100 flying!
Today we start a new series dedicated to amateur radio for
cheapskates. Ham radio has a reputation as a “rich old guy” hobby, a
reputation that it probably deserves to some degree. Pick up a glossy
catalog from DX Engineering or cruise their website, and you’ll see that
getting into the latest and greatest gear is not an exercise for the
financially challenged. And thus the image persists of the recent
retiree, long past the expense and time required to raise a family and
suddenly with time on his hands, gleefully adding just one more piece of
expensive gear to an already well-appointed ham shack to “chew the rag”
with his “OMs”.
As I pointed out a few years back in “My Beef With Ham Radio”,
I’m an inactive ham. My main reason for not practicing is that I’m not a
fan of talking to strangers, but there’s a financial component to my
reticence as well – it’s hard to spend a lot of money on gear when you
don’t have a lot to talk about. I suspect that there are a lot of
would-be hams out there who are turned off from the hobby by its
perceived expense, and perhaps a few like me who are on the mic-shy
side.
This series is aimed at dispelling the myth that one needs buckets of
money to be a ham, and that jawboning is the only thing one does on the
air. Each installment will feature a project that will move you further
along your ham journey that can be completed for no more than $50 or
so. Wherever possible, I’ll be building the project or testing the
activity myself so I can pursue my own goal of actually using my license
for a change.
(A shout-out to Robert for suggesting this series, and for graciously allowing me to run with his idea.)
Getting Your Ticket
The licensing of amateur radio stations in the United States goes all
the way back to 1912. (I’m concentrating on US laws and customs
regarding the amateur radio service simply because that’s where I live;
please feel free to chip in on the comments section about differences in
other countries.) Anyone who wants to operate on the bands reserved for
the amateur radio service has to be licensed by the Federal
Communication Commission. Unlicensed individuals are free – and
encouraged – to listen in on the bands, but if you don’t have a license,
you can’t transmit. And trust me, the local hams, with know-how,
equipment, and all the time in the world, will find you, resulting in an
unpleasant encounter with the FCC.
There’s really no reason not to get a license anyway. This will be
among the cheapest parts of a ham’s journey, and perhaps even free. To
earn a license you’ll need to pass a written exam, but before taking the
plunge you’ll need to know a little about the classes of amateur radio
licenses, and the privileges they bestow.
The current entry-level license class in the US is called Technician
class; the old Novice class was eliminated in 2000, along with the Morse
code requirement for all classes. Technicians have privileges to
operate mainly on the upper frequencies, primarily on the 2-meter (144
MHz) and 70-cm (420 MHz) bands in phone mode, which means voice
transmissions. Technicians also have access to small slices of the
10-meter band using data modes, and small sections of 15-, 40-, and
80-meters if they learn Morse or use a computer to send and receive it.
This limits the Technician to mainly local communications, but there’s
plenty to do and loads to learn on these bands.
The
band plan for US hams. Note that Technicians only have phone (voice)
privileges on 10 meters and below; the long haul bands are off limits
unless you use Morse. Source: ARRL.org
Practice, Practice, Practice
Even with all the limitations, a Technician license still offers
access to a lot of spectrum and serves as the gateway to the next two
classes, General and Extra. Everyone has to start with a Technician
license, which requires passing a 35-question multiple choice
examination. The exam is standardized with questions selected from a fixed pool, with topics ranging from knowing FCC Part 97 rules
to basic electronics and RF theory. The exam is pretty easy, especially
for anyone with a background in electronics. In fact, many complete
newbies come to exam sessions after having run through enough online
practice tests to see every possible pool question and pass the exam
without understanding a thing about radios or electronics. There are
lively debates over whether that’s a good thing or not – personally, I’m
not a fan of it – but it is what it is; the Technician exam is dead
easy.
Your investment in a Technician license will be minimal, and mostly
consists of the time it takes to study. Online practice tests – I
recommend the tests on QRZ.com
– are free to take as many times as you need to. Some ham clubs offer
local classes aimed at helping you to prepare, and those generally
charge only a nominal fee. There are even one-day intensive “ham cram” sessions where you’re guided through all the material and take the exam at the end of the day.
Exam sessions are run by Volunteer Exam Coordinators (VECs)
Volunteer Examiners (VEs), hams who have special training in
administering and grading exams. They too charge only a nominal fee – I
think I paid $15 – and may even waive the fee under certain
circumstances. There are also occasional special events like the annual Field Day, where hams set up tents and booths in public places as an outreach to the public, where exams are often administered for free.
Honestly, getting your Technician license is about as low impact as
the amateur radio hobby gets. Once you can consistently pass practice
tests online, the actual exam is a breeze. Exams are graded on the spot
so you’ll know instantly how you did, and you can even take the next
exam for no extra charge if you’re ready. Give it a shot even if you
haven’t studied – I nearly passed my Extra exam going in cold after I
aced my General.
Next Time
In the next installment I’ll start discussing what the newly minted
Technician can do with his or her license. It may seem like a pipe dream
to get on the air for less than $50, but it’s surprising what’s
available these days, and you’ll find that fifty dollars can go a long
way toward making your first contact.
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.
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.
Television
In
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
(TRF) design.
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.
Construction
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
V.
This
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.
Nuvistors
This
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
operation.
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.
We’ve seen old satellite LNAs repurposed to radio telescopes. If you think you don’t have room for a radio telescope, think again.
