Comparing Shortwave Antennas With RTL-SDR And Python

September 5, 2020 by Danie Conradie 7 Comments

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” →

SDR Transmitting Gets The Power

August 29, 2020 by Al Williams 28 Comments

Most hobby-grade software defined radio setups don’t transmit. Of the few that do, most of them put out anemic levels around one milliwatt or so. If you want to do something outside of the lab, you’ll need an amplifier and that’s what [Tech Minds] shows how to do in a recent video. (Embedded below.)

The video covers LimeSDR, HackRF, and the Pluto SDR, although the amplifiers should work with any transmitter. The SPF5189Z module is quite cheap and covers 50 MHz to 4 GHz, amplifying everything you throw at it. The downside is that it will amplify everything you throw at it, even parts of the signal you don’t want, such as spurs and harmonics.

Continue reading “SDR Transmitting Gets The Power” →

Auxiliary Display Makes Ham Radio Field Operations Easier

August 29, 2020 by Dan Maloney 14 Comments

As popular as the venerable Yaesu FT-817 transceiver might be with amateur radio operators, it’s not without its flaws, particularly in the user interface department. [Andy (G7UHN)] is painfully familiar with these flaws, so he designed this auxiliary display and control panel for the FT-817 to make operating it a little easier.

There are a ton of ways to enjoy ham radio, but one of the more popular ways is to bust out of the shack and operate in the great outdoors. From the seashore to mountain peaks, hams love giving their rigs some fresh air and sunshine. The battery-powered, multimode, all-band FT-817 is great for these jaunts, but to fit as much radio into a small package as they did, Yaesu engineers had to compromise on the controls. Rather than bristling with buttons, many of the most-used features of the radio are buried within menus that require multiple clicks and twists to access.

[Andy]’s solution is a PCB bearing an Arduino Nano, an LCD screen, and a whole bunch of actual buttons. The board sits on top of the case and talks to the radio over a 8-pin mini-DIN cable using both documented and undocumented CAT, or Computer Aided Transceiver commands. The LCD displays the current status of various features and the buttons provide easy access to changing them, essentially by sending keystrokes to the radio.

Hats off to [Andy] for tackling this project. The only other FT-817 hack we’ve seen before was useful but far simpler, and didn’t require KiCad, which [Andy] had to teach himself for this one.

Damage To Arecibo Leaves Gaping Hole In Astronomy

August 24, 2020 by Tom Nardi 69 Comments

In the early morning hours of August 10th, a support cable at the Arecibo Observatory pulled lose from its mount and crashed through the face of the primary reflector below. Images taken from below the iconic 305 meter dish, made famous by films such as Contact and GoldenEye, show an incredible amount of damage. The section of thick cable, estimated to weigh in at around 6,000 kilograms (13,000 pounds), had little difficulty tearing through the reflector’s thin mesh construction.

Worse still, the cable also struck the so-called “Gregorian dome”, the structure suspended over the dish where the sensitive instruments are mounted. At the time of this writing it’s still unclear as to whether or not any of that instrumentation has been damaged, though NASA at least has said that the equipment they operate inside the dome appears to have survived unscathed. At the very least, the damage to the dome structure itself will need to be addressed before the Observatory can resume normal operations.

The Arecibo Observatory by JidoBG [CC-BY-SA 4.0]

But how long will the repairs take, and who’s going to pay for them? It’s no secret that funding for the 60 year old telescope has been difficult to come by since at least the early 2000s. The cost of repairing the relatively minor damage to the telescope sustained during Hurricane Maria in 2017 may have been enough to shutter the installation permanently if it hadn’t been for a consortium led by the University of Central Florida. They agreed to share the burden of operating the Observatory with the National Science Foundation and put up several million dollars of additional funding.

It’s far too early to know how much time and money it will take to get Arecibo Observatory back up to operational status, but with the current world situation, it seems likely the telescope will be out of commission for at least the rest of the year. Given the fact that repairs from the 2017 damage still haven’t been completed, perhaps even longer than that. In the meantime, astronomers around the globe are left without this wholly unique resource.

Continue reading “Damage To Arecibo Leaves Gaping Hole In Astronomy” →

Mobile Transmitter Gets Internal GPS And Bluetooth

August 23, 2020 by Tom Nardi 4 Comments

While [Selim Olcer] was relatively happy with his Kenwood TM-D710a radio, he didn’t like the fact that it needed a bulky external GPS “backpack” for APRS location data. So he decided to crack open the head unit and see if he couldn’t integrate his own GPS hardware (machine translation). Not only did he succeed, but he even threw in Bluetooth compatibility for good measure.

With the repair manual circuit diagrams in hand, it was no problem to find the GPS RX and TX lines that were being broken out to the external connector. Unfortunately, the radio’s electronics are all 5 volts and the GPS module [Selim] wanted to use was only 3.3 V. So he came up with a small PCB that included not only the voltage regulator to power the GPS module, but also some voltage-dividers to level shift those signals.

Since the Kenwood TM-D710a was already designed to accept a GPS upgrade module, he just needed to change some configuration options in the radio’s menus for it to see the new hardware. Technically the project was done at this point, but since there was still room in the case and he had a GPS module spitting out NMEA sentences, [Selim] tacked on a common Bluetooth serial module so he could see the position information on his smartphone. With an application like APRSdroid, he now has a nice moving map display using the position pulled from the radio’s GPS.

With this modification done it looks like the head unit is ready to go, but that’s only the beginning for a mobile rig. Now we want to see how he integrates the whole thing into the car.

Antenna Pulls In AM Stations

August 19, 2020 by Al Williams 26 Comments

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” →

Virtual Software Defined Radio

August 7, 2020 by Al Williams 5 Comments

Software defined radio or SDR has changed the radio landscape forever. But to use one you need to buy some kind of hardware right? Maybe not. As [Tech Minds] shows in a recent video there are plenty of SDRs publically available on the Internet. We know that isn’t news, but the video does cover several different methods of finding and using SDR receivers including many that run totally in the browser.

Of course, there are a lot of reasons you might want to borrow an alien radio receiver, even if you have your own hardware. Maybe you don’t have a great antenna or maybe you want to hear a signal — maybe even your own — from a different location.

Continue reading “Virtual Software Defined Radio” →