It stands to reason, that should you wish to communicate with a satellite, whatever antenna you use should point at that satellite. Some of us have done this by hand, following the bright dot of the space station in the night sky. Still, for anything more serious than trying to catch a fleeting SSTV image, a more robust solution is called for. In other words, a motorized antenna rotator, and AntRunner from [Wuxx] is just the ticket. Better still, it’s portable for those /p operating sessions off the beaten track.
The rotator itself is an az-el design with a couple of geared stepper motors. The full mechanism design has been published, but it shouldn’t be too difficult to copy. The interesting part is the controller and software, which can work with Gpredict, Hamlib, and SDR for automated satellite tracking. The controller is as straightforward as an ESP32 running the ESP port of GRBL.
In the “old” days, people were used to the idea that radio communication isn’t always perfect. AM radio had cracks and pops and if you had to make a call with a radiophone, you expected it to be unreliable and maybe even impossible at a given time. Modern technology, satellites, and a host of other things have changed and now radio is usually super reliable and high-fidelity. Usually. However, a magnitude 7.9 solar flare this week reminded radio users in Africa and the Middle East that radio isn’t always going to get through. At least for about an hour.
It happened at around 10 AM GMT when that part of the world was facing the sun. Apparently, a coronal mass ejection accompanied the flare, so more electromagnetic disruption may be on its way.
The culprit seems to be an unusually active sunspot which is expected to die down soon. Interestingly, there is also a coronal hole in the sun where the solar wind blows at a higher than usual rate. Want to keep abreast of the solar weather? There’s a website for that.
Amateur radio operators have played a longstanding game of “Will It Antenna?” If there’s something even marginally conductive and remotely resonant, a ham has probably tried to make an antenna out of it. Some of these expedient antennas actually turn out to be surprisingly effective, but as we can see from this in-depth analysis of the characteristics of tape measure antennas, a lot of that is probably down to luck.
At first glance, tape measure antennas seem to have a lot going for them (just for clarification, most tape measure antennas use only the spring steel blade of a tape measure, not the case or retraction mechanism — although we have seen that done.) Tape measures can be rolled up or folded down for storage, and they’ll spring back out when released to form a stiff, mostly self-supporting structure.
But [fvfilippetti] suspected that tape measures might have some electrical drawbacks, thanks to the skin effect. That’s the tendency for current to flow on the outside of a conductor, which at lower frequencies on conductors with a round cross-section turns out to be not a huge problem. But in a thin, rectangular conductor, a little finite element method magnetics (FEMM) analysis revealed that most of the current is carried in very small areas, resulting in high electrical resistance — an order of magnitude greater than a round conductor. Add in the high permittivity of the carbon steel material of the blade, and you end up something more like what [fvfilippetti] calls “a tape measure dummy load.
One possible solution: stripping the paint off the blade and copper plating it. It’s not clear if this was tried; we’d think it would be difficult to accomplish, but not impossible — and surely worth a try.
The average person’s perception of a ham radio operator, assuming they even know what that means, is more than likely some graybeard huddled over the knobs of a war-surplus transmitter in the wee small hours of the morning. It’s a mental image that, admittedly, isn’t entirely off the mark in some cases. But it’s also a gross over-simplification, and a generalization that isn’t doing the hobby any favors when it comes to bringing in new blood.
In reality, a modern ham’s toolkit includes a wide array of technologies that are about as far away from your grandfather’s kit-built rig as could be — and there’s exciting new protocols and tools on the horizon. To ensure a bright future for amateur radio, these technologies need to be nurtured the word needs to be spread about what they can do. Along the way, we’ll also need to push back against stereotypes that can hinder younger operators from signing on.
On the forefront of these efforts is Amateur Radio Digital Communications (ARDC), a private foundation dedicated to supporting amateur radio and digital communication by providing grants to scholarships, educational programs, and promising open source technical projects. For this week’s Hack Chat, ARDC Executive Director Rosy Schechter (KJ7RYV) and Staff Lead John Hays (K7VE) dropped by to talk about the future of radio and digital communications.
Rosy kicked things off with a brief overview of ARDC’s fascinating history. The story starts in 1981, when Hank Magnuski had the incredible foresight to realize that amateur radio packet networks could benefit from having a dedicated block of IP addresses. In those early days, running out of addresses was all but unimaginable, so he had no trouble securing 16.7 million IPs for use by licensed amateur radio operators. This block of addresses, known as AMPRNet and then later 44Net, was administered by volunteers until ARDC was formed in 2011 and took over ownership. In 2019, the decision was made to sell off about four million of the remaining IP addresses — the proceeds of which went into an endowment that now funds the foundation’s grant programs.
Of all the recipients of ARDC grants, the M17 project garnered the most interest during the Chat. This community of open source developers and radio enthusiasts is developing a next-generation digital radio protocol for data and voice that’s unencumbered by patents and royalties. In their own words, M17 is focused on “radio hardware designs that can be copied and built by anyone, software that anyone has the freedom to modify and share to suit their own needs, and other open systems that respect your freedom to tinker.” They’re definitely our kind of folks — we first covered the project in 2020, and are keen to see it develop further.
John says the foundation has approximately $6 million each year they can dole out, and that while there’s certainly no shortage of worthwhile projects to support as it is, they’re always looking for new applicants. The instructions and guides for grant applications are still being refined, but there’s at least one hard requirement for any project that wants to be funded by the ARDC: it must be open source and available to the general amateur population.
Of course, all this new technology is moot if there’s nobody to use it. It’s no secret that getting young people interested in amateur radio has been a challenge, and frankly, it’s little surprise. When a teenager can already contact anyone on the planet using the smartphone in their pocket, getting a ham license doesn’t hold quite the same allure as it did to earlier generations.
The end result is that awareness among youth is low. During the Chat, one participant recounted how he had to put Netflix’s Stranger Things on pause so he could explain to his teenage son how the characters in the 1980s set show were able to communicate across long distances using a homemade radio. Think about that for a minute — in a show about nightmarish creatures invading our world from an alternate dimension, the hardest thing for this young man to wrap his head around was the fact a group of teenagers would be able to keep in touch with each other without the Internet or phone lines to connect them.
So its no surprise that John says the ARDC is actively looking for programs which can help improve the demographics of amateur radio. The foundation is looking to not only bring younger people onboard, but also reach out to groups that have been traditionally underrepresented in the hobby. As an example, he points to a grant awarded to the Bridgerland Amateur Radio Club (BARC) last year to bolster their youth engagement program. Funds went towards putting together a portable rig that would allow students to communicate with the International Space Station, and the development of hands-on workshops where teens will be able to launch, track, and recover payloads on a high altitude balloon. Let’s see them do that on their fancy new smartphone.
We want to not only thank Rosy Schechter and John Hays for taking part in this week’s Hack Chat, but everyone else at Amateur Radio Digital Communications for their efforts to support the present and future of amateur radio and digital communication.
The Hack Chat is a weekly online chat session hosted by leading experts from all corners of the hardware hacking universe. It’s a great way for hackers connect in a fun and informal way, but if you can’t make it live, these overview posts as well as the transcripts posted to Hackaday.io make sure you don’t miss out.
[David], DL1DN, is an Amateur Radio enthusiast with a penchant for low-power (QRP) portable operations. Recently he was out and about, and found that 10 m propagation was wide open. Not discouraged by having forgotten his antenna, he kludges up a makeshift one using a 20 cm length of aluminum foil (see video demonstration below the break). [David] wasn’t completely unprepared, as he did have the loading coil for his portable 20 m antenna, but was missing the telescoping whip. He calculated the whip length should be around 20 cm for 10 m operation, and crinkles up a sheet of foil the approximate length. He tunes it to length by rolling the tip to shorten the “whip” until he gets an SWR minimum.
With music consumption having long ago moved to a streaming model in many parts of the world, it sometimes feels as though, just like the rotary telephone dial, kids might not even know what a radio was, let alone own one. But there was a time when broadcasting pop music over the airwaves was a deeply subversive activity for Europeans at least, as the lumbering state monopoly broadcasters were challenged by illegal pirate stations carrying the cutting edge music they had failed to provide. [Ringway Manchester] has the story of one such pirate station which broadcast across the city for a few years in the 1970s, and it’s a fascinating tale indeed.
It takes the form of a series of six videos, the first of which we’ve embedded below the break. The next installment is placed as an embedded link at the end of each video, and it’s worth sitting down for the full set.
The action starts in early 1973 when a group of young radio enthusiast friends, left without access to a station of their taste by Government crackdowns on ship-based pirate stations, decided to try their hand with a land-based alternative. Called Radio Aquarius, it would broadcast on and off both the medium wave (or AM) and the FM broadcast bands over the next couple of years. Its story is one of improvised transmitters powered by car batteries broadcasting from hilltops, woodland, derelict houses, and even a Cold War nuclear bunker, and develops into a cat-and-mouse game between the youths and the local post office agency tasked with policing the spectrum. Finally having been caught once too many times, they disband Radio Aquarius and go on to careers in the radio business.
The tale has some tech, some social history, and plenty of excitement, but the surprise is in how innocent it all seems compared to the much more aggressively commercial pirate stations that would be a feature of later decades. We’d have listened, had we been there!
The tech news channels were recently abuzz with stories about strange signals coming back from Voyager 1. While the usual suspects jumped to the usual conclusions — aliens!! — in the absence of a firm explanation for the anomaly, some of us looked at this event as an opportunity to marvel at the fact that the two Voyager spacecraft, now in excess of 40 years old, are still in constant contact with those of us back on Earth, and this despite having covered around 20 billion kilometers in one of the most hostile environments imaginable.
Like many NASA programs, Voyager has far exceeded its original design goals, and is still reporting back useful science data to this day. But how is that even possible? What 1970s-era radio technology made it onto the twin space probes that allowed it to not only fulfill their primary mission of exploring the outer planets, but also let them go into an extended mission to interstellar space, and still remain in two-way contact? As it turns out, there’s nothing magical about Voyager’s radio — just solid engineering seasoned with a healthy dash of redundancy, and a fair bit of good luck over the years.
The Big Dish
For a program that in many ways defined the post-Apollo age of planetary exploration, Voyager was conceived surprisingly early. The complex mission profile had its origins in the “Planetary Grand Tour” concept of the mid-1960s, which was planned to take advantage of an alignment of the outer planets that would occur in the late 1970s. If launched at just the right time, a probe would be able to reach Jupiter, Saturn, Uranus, and Neptune using only gravitational assists after its initial powered boost, before being flung out on a course that would eventually take it out into interstellar space.
The idea of visiting all the outer planets was too enticing to pass up, and with the success of the Pioneer missions to Jupiter serving as dress rehearsals, the Voyager program was designed. Like all NASA programs, Voyager had certain primary mission goals, a minimum set of planetary science experiments that project managers were reasonably sure they could accomplish. The Voyager spacecraft were designed to meet these core mission goals, but planners also hoped that the vehicles would survive past their final planetary encounters and provide valuable data as they crossed the void. And so the hardware, both in the spacecraft and on the ground, reflects that hope.
The most prominent physical feature of both the ground stations of the Deep Space Network (DSN), which we’ve covered in-depth already, and the Voyager spacecraft themselves are their parabolic dish antennas. While the scale may differ — the DSN sports telescopes up to 70 meters across — the Voyager twins were each launched with the largest dish that could fit into the fairing of the Titan IIIE launch vehicle.
The primary reflector of the High Gain Antenna (HGA) on each Voyager spacecraft is a parabolic dish 3.7 meters in diameter. The dish is made from honeycomb aluminum that’s covered with a graphite-impregnated epoxy laminate skin. The surface of the reflector is finished to a high degree of smoothness, with a surface precision of 250 μm, which is needed for use in both the S-band (2.3 GHz), used for uplink and downlink, and X-band (8.4 GHz), which is downlink only.
Like their Earth-bound counterparts in the DSN, the Voyager antennas are a Cassegrain reflector design, which uses a Frequency Selective Subreflector (FSS) at the focus of the primary reflector. The subreflector focuses and corrects incoming X-band waves back down toward the center of the primary dish, where the X-band feed horn is located. This arrangement provides about 48 dBi of gain and a beamwidth of 0.5° on the X-band. The S-band arrangement is a little different, with the feed horn located inside the subreflector. The frequency-selective nature of the subreflector material allows S-band signals to pass right through it and illuminate the primary reflector directly. This gives about 36 dBi of gain in the S-band, with a beamwidth of 2.3°. There’s also a low-gain S-band antenna with a more-or-less cardioid radiation pattern located on the Earth-facing side of the subreflector assembly, but that was only used for the first 80 days of the mission.
Two Is One
Three of the ten bays on each Voyager’s bus are dedicated to the transmitters, receivers, amplifiers, and modulators of the Radio Frequency Subsystem, or RFS. As with all high-risk space missions, redundancy is the name of the game — almost every potential single point of failure in the RFS has some sort of backup, an engineering design decision that has proven mission-saving in more than one instance on both spacecraft over the last 40 years.
On the uplink side, each Voyager has two S-band double-conversion superhet receivers. In April of 1978, barely a year before its scheduled encounter with Jupiter, the primary S-band receiver on Voyager 2 was shut down by fault-protection algorithms on the spacecraft that failed to pick up any commands from Earth for an extended period. The backup receiver was switched on, but that was found to have a bad capacitor in the phase-locked loop circuit intended to adjust for Doppler-shift changes in frequency due primarily to the movement of the Earth. Mission controllers commanded the spacecraft to switch back to the primary receiver, but that failed again, leaving Voyager 2 without any way to be commanded from the ground.
Luckily, the fault-protection routines switched the backup receiver back on after a week of no communication, but this left controllers in a jam. To continue the mission, they needed to find a way to use the wonky backup receiver to command the spacecraft. They came up with a complex scheme where DSN controllers take a guess at what the uplink frequency will be based on the predicted Doppler shift. The trouble is, thanks to the bad capacitor, the signal needs to be within 100 Hz of the lock frequency of the receiver, and that frequency changes with the temperature of the receiver, by about 400 Hz per degree. This means controllers need to perform tests twice a week to determine the current lock frequency, and also let the spacecraft stabilize thermally for three days after uplinking any commands that might change the temperature on the spacecraft.
On the transmit side, both the X-band and S-band transmitters use separate exciters and amplifiers, and again, multiple of each for redundancy. Although downlink is primarily via the X-band transmitter, either of the two S-band exciters can be fed into either of two different power amplifiers. A Solid State Amplifier (SSA) provides a selectable power output of either 6 W or 15 W to the feedhorn, while a separate traveling-wave tube amplifier (TWTA) provides either 6.5 W or 19 W. The dual X-band exciters, which use the S-band exciters as their frequency reference, use one of two dedicated TWTAs, each of which can send either 12 W or 18W to the high-gain antenna.
The redundancy built into the downlink side of the radio system would play a role in saving the primary mission on both spacecraft. In October of 1987, Voyager 1 suffered a failure in one of the X-band TWTAs. A little more than a year later, Voyager 2 experienced the same issue. Both spacecraft were able to switch to the other TWTA, allowing Voyager 1 to send back the famous “Family Portrait” of the Solar system including the Pale Blue Dot picture of Earth, and for Voyager 2 to send data back from its flyby of Neptune in 1989.
Slower and Slower
The radio systems on the Voyager systems were primarily designed to support the planetary flybys, and so were optimized to stream as much science data as possible back to the DSN. The close approaches to each of the outer planets meant each spacecraft accelerated dramatically during the flybys, right at the moment of maximum data production from the ten science instruments onboard. To avoid bottlenecks, each Voyager included a Digital Tape Recorder (DTR), which was essentially a fancy 8-track tape deck, to buffer science data for later downlink.
Also, the increasing distance to each Voyager has drastically decreased the bandwidth available to downlink science data. When the spacecraft made their first flybys of Jupiter, data streamed at a relatively peppy 115,200 bits per second. Now, with the spacecraft each approaching a full light-day away, data drips in at only 160 bps. Uplinked commands are even slower, a mere 16 bps, and are blasted across space from the DSN’s 70-meter dish antennas using 18 kW of power. The uplink path loss over the current 23 billion kilometer distance to Voyager 1 exceeds 200 dB; on the downlink side, the DSN telescopes have to dig a signal that has faded to the attowatt (10-18 W) range.
That the radio systems of Voyager 1 and Voyager 2 worked at all while they were still in the main part of their planetary mission is a technical achievement worth celebrating. The fact that both spacecraft are still communicating, despite the challenges of four decades in space and multiple system failures, is nearly a miracle.
If there’s one thing that amateur radio operators are good at, it’s turning just about anything into an antenna. And hams have a long history of portable operations, too, where they drag a (sometimes) minimalist setup of gear into the woods and set up shop to bag some contacts. Getting the two together, as with this field-portable antenna made from a tape measure, is a double win in any ham’s book.
For [Paul (OM0ET)], this build seems motivated mainly by the portability aspect, and less by the “will it antenna?” challenge. In keeping with that, he chose a 50-meter steel tape measure as the basis of the build. This isn’t one of those retractable tape measures, mind you — just a long strip of flexible metal on a wind-up spool in a plastic case. His idea was to use the tape as the radiator for an end-fed halfwave, or EFHW, antenna, a multiband design that’s a popular option for hams operating from the 80-m band down to the 10-m band. EFHW antennas require an impedance-matching transformer, a miniature version of which [Paul] built and tucked within the tape measure case, along with a BNC connector to connect to the radio and a flying lead to connect to the tape.
Since a half-wave antenna is half the length of the target wavelength, [Paul] cut off the last ten meters of the tape to save a little weight. He also scratched off the coating on the tape at about the 40-meter mark, to make good contact with the alligator clip on the flying lead. The first video below details the build, while the second video shows the antenna under test in the field, where it met all of the initial criteria of portability and ease of deployment.