Comparing Shortwave Antennas With RTL-SDR And Python

Measuring the performance of antennas in absolute terms that can involve a lot of expensive equipment and specialized facilities. For practical applications, especially when building antennas, comparing performance in relative terms is more practical. Using cheap RTL-SDR dongles and Python, [Eric Urban] was able to compare the performance of two shortwave/HF antennas, and documented the entire process.

The two antennas in question was a single band inverted-L and smaller broadband T3FD antenna. [Eric] first gathered performance data for each over few days, connected to separate PCs with RTL-SDRs via low-pass filters. These were set up to receive FT8 transmissions, a popular digital ham radio mode, which allowed [Eric] to automate data collection completely. GQRX, a software receiver, converted the signals to audio, which was then piped into WSJT-X for demodulation.

Data for each received FT8 transmission was recorded to a log file. [Eric] also modified GQRX and WSJT-X to give him all the remote control features he needed to automatically change frequencies. Between the two antenna setups, more than 100,000 FT8 transmissions were logged. Using the recorded data and Python he compared the number of received transmissions, the distance, and the heading to the transmitters, using the location information included in many FT8 transmissions. Where the same transmission was received by both antennas, the signal-to-noise ratios was compared.

From all this data, [Eric] was able to learn that the inverted-L antenna performed better than the T3FD antenna on three of the four frequency bands that were tested. He also discovered that the inverted-L appeared to be “deaf” in one particular direction. Although the tests weren’t perfect, it is impressive how much practical data [Eric] was able to gather with low-cost hardware. Continue reading “Comparing Shortwave Antennas With RTL-SDR And Python”

Pocket TV Now Shows The Inspection Channel 24/7

Those little pocket TVs were quite the cool gadget back in the ’80s and ’90s, but today they’re pretty much useless at least for their intended purpose of watching analog television. (If someone is out there making tiny digital-to-analog converter boxes for these things, please let us know.)

Now that analog pocket TVs are obsolete, they’re finally affordable enough for hacking into a useful tool like an inspection camera. [technichenews] found a nice Casio TV and a suitable analog pinhole camera that also does IR. Since the camera has RCA plugs and the TV’s video input is some long-gone proprietary 3.5mm cable, [technichenews] made a new video-only cable by soldering the yellow RCA wires up to the cable from an old pair of headphones. Power for the camera comes from a universal wall wart set to 12V.

Our favorite part of this project is the way that [technichenews] leveraged what is arguably the most useless part of the TV — the antenna — into the star. Their plan is to use the camera to peer into small engines, so by mounting it on the end of the antenna, it will become a telescoping, ball-jointed, all-seeing eye. You can inspect the build video after the break.

Need a faster, easier way to take a closer look without breaking the bank? We hear those slim earwax-inspection cameras are pretty good.

Continue reading “Pocket TV Now Shows The Inspection Channel 24/7”

Antenna Pulls In AM Stations

While we can’t argue that FM has superior audio quality and digital streaming allows even higher quality in addition to worldwide access, there’s still something magic about hearing a weak and fading AM signal from thousands of miles away with nothing between the broadcaster’s antenna and yours. If you can’t have a big antenna — or even if you can — a loop antenna can help your big antenna fit in less space. In the video after the break, [TheOffsetVolt] covers an AM loop and shows how it can pull in distant AM stations.

Continuing with the educational radio he’s talked about before,  he adds a loop antenna that is two feet on each side of a square, making it four square feet in area. Although he calls it an amplifier, it’s really just a passive tuned circuit that couples to the radio’s built-in antenna. There’s no actual connection between the antenna and the radio.

We aren’t sure if the reradiation explanation is really what’s happening, or if it is just transformer coupled to the main antenna. But either way, it seems to work well. You can think of this as adding a preselector to the existing radio. Loop antennas are directional, so this design could work as a direction finder.

We have seen many loop antennas, some with novel construction methods.  Some even tune themselves.

Continue reading “Antenna Pulls In AM Stations”

Son Of Rothult

We are continuously inspired by our readers which is why we share what we love, and that inspiration flows both ways. [jetpilot305] connected a Rothult unit to the Arduino IDE in response to Ripping up a Rothult. Consider us flattered. There are several factors at play here. One, the Arduino banner covers a lot of programmable hardware, and it is a powerful tool in a hardware hacker’s belt. Two, someone saw a tool they wanted to control and made it happen. Three, it’s a piece of (minimal) security hardware, but who knows where that can scale. The secure is made accessible.

The Github upload instructions are illustrated, and you know we appreciate documentation. There are a couple of tables for the controller pins and header for your convenience. You will be compiling your sketch in Arduino’s IDE, but uploading through ST-Link across some wires you will have to solder. We are in advanced territory now, but keep this inspiration train going and drop us a tip to share something you make with this miniature deadbolt.

Locks and security are our bread and butter, so enjoy some physical key appreciation and digital lock love.

Hackaday Links Column Banner

Hackaday Links: July 19, 2020

Care to flex your ethical hacker muscles? The Defense Advanced Research Projects Agency, better known as DARPA, is running its first-ever bug-bounty program. The event is called “Finding Exploits to Thwart Tampering”, or FETT — get it? Bounty hunter? Fett? — and is designed to stress-test security hardware developed through DARPA’s System Security Integration Through Hardware and Firmware, or SSITH. Tortured backronyms and pop culture references aside, FETT will start this month and go through September. This is not an open challenge per se; rather, the Red Team will be coordinated by crowdsourced security research company Synack, who has called for security researchers to sign on.

The Linux kernel development team has decided to join the trend away from insensitive terminology like “master/slave” and “blacklist/whitelist” in coding style. A July 4 proposal by kernel maintainer Dan Williams goes into some detail on the logic of making the change, and it’s quite convincing stuff. It’s hard to argue with the fact that code reviewers can easily be distracted by coding style changes, so replacing terms that have become lightning rods only makes sense. Linus himself has signed off on the changes for all future code; the current terminology will only be allowed for purposes of maintaining older code.

Some stories just leap off the screen when you’re scanning headlines, and a story with the term “narco-antennas” practically begs further investigation. It turns out that the drug cartels in Mexico (and probably elsewhere, but the story focused on Mexico) are quite sophisticated in terms of communications technology. Eschewing cell phones for some of their communication needs for obvious reasons, they still apparently leverage the cell system by installing their own transceivers at cell sites. This can lead to some tense moments for the engineers who maintain legitimate gear at these sites; the story above recounts one hapless tech who powered down a site to make some repairs only to be confronted by armed men upset about the loss of their radios. It’s a fascinating look at the underworld and their technology, and we can’t help but feel for the men and women who have to face down these criminals just to do their jobs.

Way back in January — remember January? — we kicked off the 2020 Hack Chat series with a fellow named Alberto Caballero, principal investigator of the Habitable Exoplanet Hunting Project. At the time, I was blown away by the fact that the tiny changes in intensity caused by planets transiting across their star’s face were detectable on Earth with instruments an amateur astronomer could easily afford. And now, the project’s crowdsourced planet hunters have hit pay dirt, with the discovery of a Saturn-sized exoplanet in orbit within the habitable zone around star GJ 3470, also known as Gliese 3470, a red dwarf about 30 parsecs away in the constellation Cancer. Their paper is still in preprint and hasn’t been peer-reviewed yet, but it’s exciting to see this kind of citizen science being done, and we’d like to congratulate the team on their achievement and wish them continued luck in their search for “Earth 2.0”

And finally, if you can’t stand the idea that future archaeologists may someday pore over your code in an attempt to understand the digital lives of their long-dead forebears, then you might want to skip this story about how GitHub shipped 21 terabytes of open-source code to cold storage. The destination for the data, contained on reels of archive film and shipped on two pallets, is the world’s long-term memory: the Artic World Archive on the island of Svalbard. Perhaps better known for the Svalbard Seed Vault, where the genetic diversity of the world’s plants is stored, the Artic Code Vault is in a nearby abandoned coal mine and set deep within the permafrost. The rationale for making the effort to preserve code makes for some interesting reading, but we can’t help but feel that like the graffitists of Pompeii, if we’d known someone would be reading this stuff in a thousand years, we might have edited out a few things.

NASA Making Big Upgrades To Their Big Dish DSS43

When it comes to antenna projects, we usually cover little ones here. From copper traces on a circuit board to hand-made units for ham radio. But every once in a while it’s fun to look at the opposite end of the spectrum, and anyone who craves such change of pace should check out DSS43’s upgrade currently underway.

Part of NASA’s Deep Space Network (DSN) built to communicate with spacecraft that venture far beyond Earth, Deep Space Station 43 is a large dish antenna with a diameter of 70 meters and largest of the Canberra, Australia DSN complex. However, the raw reflective surface area is only as good as the radio equipment at its center, which are now outdated and thus focus of this round of upgrades.

The NASA page linked above offers a few pieces of fun trivia about DSS43 and its capabilities. If that whets an appetite for more, head over to Twitter for a huge treasure trove. Whoever is in charge of Canberra DSN’s Twitter account has an endless fountain of facts and very eager to share them in response to questions, usually tagged with #DSS43. Example: the weight of DSS43 is roughly 8.5 million kilograms, 4 million of which is moving structure. They also shared time lapse video clips of work in progress, one of which is embedded after the break.

Taking the uniquely capable DSS43 offline for upgrades does have some consequences, one of which is losing our ability to send commands to distant interplanetary probe Voyager 2. (Apparently smaller DSN dishes can be arrayed to receive data, but only DSS43 can send commands.) Such sacrifices are necessary as an investment for the future, with upgrade completion scheduled for January 2021. Just in time to help support Perseverance (formerly “Mars 2020”) rover‘s arrival in February and many more missions for years to come.

Continue reading “NASA Making Big Upgrades To Their Big Dish DSS43”

Life-Saving Surgery For A Telescopic Antenna

Whether it was as an impulsive youth or an impatient adult, there’s probably few among us who haven’t broken a telescopic antenna or two over the years. It doesn’t take much to put a bend in the thin walled tubing, and after that, all bets are off. So [The Amateur Engineer] couldn’t really be too upset when his son snapped the antenna off the transmitter of an old RC truck. Instead, he decided to take it apart and see how it could be repaired.

Taking a thin screwdriver to the antenna’s bottom most segment, he was able to widen up the opening enough to remove the upper sections as well as recover the broken piece and copper locking plates. He cut out the damaged area and drilled new holes for the pins on the copper plates to fit into. Inserting the repaired section back into the lowest segment was no problem, but he says it took a little trial and error before he was able to roll the edge over enough to keep the antenna from falling apart.

Buying a replacement would certainly have been easier, but as the radios in our devices have moved into the higher frequencies, these collapsible antennas have become a bit harder to come by. Modern RC vehicles operate on 2.4 GHz, so they don’t need the long antennas that the older 27 MHz systems utilized. [The Amateur Engineer] did find a few direct replacements online, but none for a price he was willing to pay.

We might have used the broken transmitter as an excuse to switch the RC vehicle over to WiFi control, but we appreciate [The Amateur Engineer] showing how this type of antenna can be disassembled and repaired if necessary.