Categorie: Hackaday

Anybody who has set up a satellite TV antenna will tell you that alignment is critical when picking up a signal from space. With a satellite dish it’s a straightforward task to tweak the position, but what happens if the dish in question is out beyond the edge of the Solar System?

We told you a few days ago about this exact issue currently facing Voyager 2, but we’re guessing Hackaday readers will want to know a little bit more about how a 50+ year old spacecraft so far from home can still sort out its antenna. The answer lies in NASA Technical Report 32-1559, Digital Canopus Tracker from 1972, which describes the instrument that notes the position of the star Canopus, which along with that of the Sun it can use to calculate the antenna bearing to reach Earth. The report makes for fascinating reading, as it describes how early-1970s technology was used to spot the star by its specific intensity and then keep it in its sights. It’s an extremely accessible design, as even the part numbers are an older version of the familiar 74 logic.

So somewhere out there in interstellar space beyond the boundary of the Solar System is a card frame full of 74 logic that’s been quietly keeping an eye on a star since the early 1970s, and the engineers from those far-off days at JPL are about to save the bacon of the current generation at NASA with their work. We hope that there are some old guys in Pasadena right now with a spring in their step.

Read our coverage of the story here.

Here in 2023 the field of electronics covers a breathtaking variety of devices and applications, but if we were to go back in time far enough we’d enter an age in which computers were few and far between, and any automated control systems would have been electromechanical at best. Back in the 1950s the semiconductor industry was in relative infancy, and at the consumer end electronics were largely synonymous with radio. [Shango066] brings us a transistor radio from that era, a Jewel TR1 from about 1958, that despite its four-transistor simplicity to our eyes would have been a rare and expensive device when new.

As you’d expect, a transistor radio heading toward its 70th birthday requires a little care to return to its former glory, and while this one is very quiet it does at least work after a fashion. The video below the break is a long one that you might wish to watch at double speed, but it takes us through the now-rare skill of fault-finding and aligning an AM radio receiver. First up are a set of very tired electrolytic capacitors whose replacement restores the volume, and then it’s clear from the lack of stations that the set has a problem at the RF end. We’re treated to the full process of aligning a superhet receiver through the relatively forgiving low-frequency medium of a medium-wave radio. Along the way, he damages one of the IF transformers and has to replace it with a modern equivalent, which we would have concealed under the can from the original.

The video may be long, but it’s worth a look for the vintage parts if not for the quality of radio stations on the air today in California. For many readers, AM broadcast is becoming a thing of the past, so we’re not sure we’ll see this very often.

A word of advice: If you see an old direct satellite TV dish put out to the curb, grab it before the trash collector does. Like microwave ovens, satellite dishes are an e-waste wonderland, and just throwing them away before taking out the good stuff would be a shame. And with dishes, the good stuff basically amounts to the bit at the end of the arm that contains the feedhorn and low-noise block downconverter (LNB).

But what does one do with such a thing once it’s harvested? Lots of stuff, including modifying it for use with the QO-100 geosynchronous satellite. That’s what [Sebastian Westerhold] and [Celin Matlinski] did with a commodity LNB, although it seems more like something scored on the cheap from one of the usual sources rather than picking through trash. Either way, these LNBs are highly integrated devices that at built specifically for satellite TV use, but with just a little persuasion can be nudged into the K-band to receive the downlink signals from hams using QO-100 as a repeater.

The mods are simple — snipping out the 25 MHz reference crystal on the LNB board and replacing it with a simple LC bandpass filter. This allows the local oscillator on the LNB to be referenced to an external signal generator; when fed with a 25.78 MHz signal, it’s enough to goose the LNB up to 10,490 MHz — right about the downlink frequency. [Sebastian] and [Celin] tested the mods and found that it was easily able to detect the third harmonics of a 3.5-ish GHz signal.

As for testing on actual downlink signals from the satellite, that’ll have to wait. For now, if you’re interested in satellite comms, and you live on the third of the planet covered by QO-100, keep an eye out for those e-waste LNBs and get to work.

There was a time when buying a new radio was something many hams could never afford to do. Then came the super cheap — and super controversial — VHF and UHF radios from China. But as they say, you get what you pay for. The often oddly named handhelds like Baofeng and Wouxun are sometimes odd to work with and may have questionable RF outputs. A new radio has a less tongue-twisting English name and many improved features for about $50 — the Talkpod A36Plus and [Josh] shows us how they work in a video that you can see below.

The new features are generally good. For example, the radio can pick up AM in the aircraft band, something most of these cheap radios won’t do. It works on VHF and UHF bands but also picks up FM broadcasts. The USB-C connector is welcome, and the screen is large and colorful. It has 500 channels and IP5 water resistance.

There were a few issues, though. If you want to use it as a scanner, it’s not very fast. The radio comes with a programming cable, but apparently, it uses an odd USB chipset that may give you some driver issues. The biggest problem, though, is that it has, according to the video, excessive spurious emissions. The power isn’t that high, and the antenna probably filters off some of it, too. But creating interference across the band isn’t very polite.

How bad are the harmonics? Well, [Josh] hooks up a spectrum analyzer and also shows how a radio tuned to the second harmonic easily picks up the transmission. Of course, no radio is perfect, but it seems like it does have very strong harmonic emissions. Of course, it may or may not be any worse than similar cheap radios. They are probably all above the legal limits, and it is just a matter of degrees.

These little radios won’t directly work the world — you need an HF radio for that, generally. They will let you connect to local repeaters, though. Some of those cheap radios can lead to interesting projects, too.

Over the past decade or so, amateur radio operators have benefited from an influx of inexpensive radios based around a much simpler design than what was typically commercially available, bringing the price of handheld dual-band or GMRS radios to around $20. This makes the hobby much more accessible, but they have generated some controversy as they tend to not perform as well and can generate spurious emissions and other RF interference that a higher quality radio might not create. But one major benefit besides cost is that they’re great for tinkering around, as their simplified design is excellent for modifying. This experimental firmware upgrade changes a lot about this Quansheng model.

With the obligatory warning out of the way that modifying a radio may violate various laws or regulations of some localities, it looks like this modified firmware really expands the capabilities of the radio. The chip that is the basis of the radio, the BK4819, has a frequency range of 18-660 MHz and 840-1300 MHz but not all of these frequencies will be allowed with a standard firmware in order to comply with various regulations. However, there’s typically no technical reason that a radio can’t operate on any arbitrary frequency within this range, so opening up the firmware can add a lot of functionality to a radio that might not otherwise be capable.

Some of the other capabilities this modified firmware opens up is the ability to receive in various other modes, such as FM and AM within the range of allowable frequencies. To take a more deep dive on what this firmware allows be sure to check out the original GitHub project page as well, and if you’re curious as to why these inexpensive radios often run afoul of radio purists and regulators alike, take a look at some of the problems others have had in Europe.

Tuning into a GPS satellite is nothing new. Your phone and your car probably do that multiple times a day. But [dereksgc] has been listening to GPS voice traffic. The traffic originates from COSPAS-SARSAT, which is a decades-old international cooperative of 45 nations and agencies that operates a worldwide search and rescue program. You can watch a video about it below.

Nominally, a person in trouble activates a 406 MHz beacon, and any of the 66 satellites that host COSPAS-SARSAT receivers can pick it up and relay information to the appropriate authorities. These beacons are often attached to aircraft or ships, but there are an increasing number of personal beacons used by campers, hikers, and others who might be in danger and out of reach of a cell phone. The first rescue from this system was in 1982. By 2021, 3,632 people were rescued thanks to the system.

The satellites that listen to the beacon frequencies don’t process the signals. They use a transponder that re-transmits anything it hears on a much higher downlink frequency. These transponders are always payloads on other satellites like navigation or weather satellites. But because the transponder doesn’t care what it hears, it sometimes rebroadcasts signals from things other than beacons. We were unclear if these were rogue radios or radios with spurious emissions in the translator’s input range.

The video has practical tips on how to tune in several of the satellites that carry these transponders. Might be a fun weekend project with a software-defined radio.

We’ve seen homebrew satellite devices, but none for an emergency beacon — we aren’t sure what the legal aspects of that would be. There are other satellites that unknowingly host pirate radio stations, too.

Dirty little secret time: although amateur radio operators talk a good game about relishing the technical challenge of building their own radio equipment, what’s really behind all the DIY gear is the fact that the really good stuff is just too expensive to buy.

A case in point is this super-low-cost RF power sensor that [Tech Minds (M0DQW)] recently built. It’s based on a design by [DL5NEG] that uses a single Schottky diode and a handful of passive components. The design is simple, but as with all things RF, details count. Chief among these details is the physical layout of the PCB, which features a stripline of precise dimensions to keep the input impedance at the expected 50 ohms. Also important are the number and locations of the vias that stitch the ground planes together on the double-sided PCB.

While [Tech Minds]’ first pass at the sensor hewed closely to the original design and used a homebrew PCB, the sensor seemed like a great candidate for translating to a commercial PCB. This version proved to be just as effective as the original, with the voltage output lining up nicely with the original calibration curves generated by [DL5NEG]. The addition of a nice extruded aluminum case and an N-type RF input made for a very professional-looking tool, not to mention a useful one.

[Tech Minds] is lucky enough to live within view of QO-100, ham radio’s first geosynchronous satellite, so this sensor will be teamed up with an ADC and a Raspberry Pi to create a wattmeter with a graphical display for his 2.4-GHz satellite operations.

Magnetic loop antennas are great if you are limited on space since they are just a potentially small loop of wire. The problem is, they are sharply tuned. You normally have an adjustment capacitor to tune the antenna to different frequencies. [TekMakerUK] built one with a motor and an Arduino that he can tune from an Android phone. You can see more about the project in the video below.

If you want to transmit, the capacitor is often the weak part of the system. Luckily, some old gear yielded a capacitor with multiple sections and enough plate distance to handle the 5W desired. Of course, motor driving a capacitor isn’t a new idea, but this setup is nice since it uses a stepper motor and a rotary encoder.

For now, the control just moves the stepper to a particular position, but long term, there are plans to have presets for each band that the Arduino can set from a single command. You might wonder how the stepper knows where it is since there are no limit switches. It turns out he just stalls the motor and assumes it is at the far limit and then moves it to the other limit (see initMotor) in the GitHub source code.

Loops are easy to hide. This isn’t, of course, the first remote loop antenna we’ve covered.

The Buzzer, also known as UVB-76 or UZB-76, has been a constant companion to anyone with a shortwave radio tuned to 4625 kHz. However, [Ringway Manchester] notes that there is now a second buzzer operating near in frequency to the original. Of course, like all mysterious stations, people try to track their origin. [Ringway] shows some older sites for the Buzzer and the current speculation on the current transmitter locations.

Of course, the real question is why? The buzzing isn’t quite nonstop. There are occasional voice messages. There are also jamming attempts, including one, apparently, by Pac Man.

Some people think the new buzzer is an image, but it doesn’t seem to be the same signal. The theory is that the buzzing is just to keep the frequency clear in case it is needed. However, we wonder if it isn’t something else. Compressed data would sound like noise.  Other theories are that the buzzing studies the ionosphere or that it is part of a doomsday system that would launch nuclear missiles. Given that the signal has broken down numerous times, this doesn’t seem likely.

What’s even stranger is that occasional background voices are audible on the signal. That implies that buzzing noise isn’t generated directly into the transmitter but is a device in front of a microphone.

We’ve speculated on the buzzer and the jamming efforts around it before. Not exactly a numbers station, but the same sort of appeal.