PI4ZLB

You used to be able to tell a die-hard ham radio operator on the road by the number and length of antennas protruding porcupine-like from their vehicle. There are still some mobile high frequency operators that have respectable car-mounted antenna farms, but they have nothing on Alfred H. Grebe. In 1919, he fitted a medium wave transmitter in his car that operated around 2 MHz. Since it needed a very large antenna, Grebe rigged a wire antenna that looked like a clothesline between the two bumpers. Obviously, you had to stop, set up your antenna, and then operate — you couldn’t talk and drive. But this may have been the world’s first automotive radio setup for voice communication.

The car had a separate battery for the radio and a dynamotor to generate high voltage for the tubes. Although many radio enthusiasts found ways to add receivers to their cars in the 1920s, it would be 1930 before Motorola made radios especially for cars in production quantities.

That wasn’t what Grebe was most famous for, though. He worked as a ship’s operator After making a few receivers for friends, he decided to open up a business. Grebe radio, though, is hardly a household name today. But he was best known for setting up radio stations, including founding the station that would eventually become WCBS, often called the father of news radio.

We always enjoy learning about radio pioneers including Edwin Armstrong and Reginald Fessenden. This is certainly a far cry even from the old mobile telephones.

A dipole antenna is easy, right? Two wires, each a quarter wavelength long, emanate from a coax or other feedline. Unless it is an off-center dipole. The length is still the same, but you move the feed point to a different part. [KB9VBR] explains how this changes the antenna’s impedance from the nominal 70 ohms of a standard dipole.

Why would you want to do that? The trick is to find a feed point that has acceptable impedance on multiple ham radio bands. Most automatic tuners can handle a certain range of mismatch so using an antenna like this with a tuner can allow one antenna to serve multiple bands with no traps or switches.

[KB9VBR] uses a 4:1 balun to convert the relatively high impedance to something close enough for a tuner to work with. A cordless soldering iron comes in handy for antenna work and in the video you can see a gas-powered iron making short work of the connections to the 14 gauge wire.

The impedance also depends on height and he suggests 30 feet, at least. Does it work? If you watch the end of the video, it apparently does. If you are in the mood for technical talk about ham antennas, you could do worse than watch this MIT video. If you want a novel take on why antennas work, you might want to read about the kink.

We often think of ham radio operators talking to exotic faraway lands, and that’s true for hams using the HF bands (below 30 MHz), especially if they have nice antennas. Modern living has made it much harder to have those big antenna farms, and today’s ham is more likely talking on VHF or UHF frequencies with very limited range under normal circumstances. Sure, you can use a repeater or bounce your signal from a satellite or the moon, but normal direct communication is normally going to be less than a typical commercial FM radio station. But on April 7th, two hams communicated across the Atlantic on 432 MHz — a UHF frequency. The distance was almost 4,000 km.

Notice we didn’t say they talked, but they communicated. The contact was via a somewhat controversial mode called FT8 which uses weak signal techniques to allow two computers to send limited amounts of information to each other. However, on April 10, the two stations reported a single sideband voice contact after they noticed the band conditions improving on the FT8 signal.

The two stations had good equipment, but nothing out of the ordinary. FG8OJ in Guadeloupe used a 100W transmitter and an 18 element yagi which is not terribly large at that frequency. D4VHF was on the Cape Verde Islands at the time of the contact. FG4ST also made a connection with D4VHF using only a vertical antenna.

Propagation was, obviously, very good to allow this to happen (the image above is from F5LEN’s prediction for that day). The theory is that the signals rode close to the ocean waves in a mode known as ducting. There were other reception reports, so the incident wasn’t isolated.

Normally this kind of thing requires active or passive bouncing of a signal. Repeaters have a limited range. The moon and satellites can take you further but require some work. Hams have even used reflections from airplanes as an in-between solution.

The Silicon Labs Si4735 is a single-chip solution for receiving AM, FM, and shortwave radio. With a bit of hacking, it even supports single sideband (SSB). All you’ve got to do is provide it with a suitable control interface, which [Ricardo Lima Caratti] has done with his recent project.

Using an Arduino Pro Mini, a handful of buttons, and a standard TFT display, [Ricardo] has put together a serviceable little receiver with a fairly impressive user interface. We especially like the horizontal bars indicating the signal to noise ratio and received signal strength. The next evolution would be to put this whole rig into some kind of enclosure, but for now he seems content to control the action with a handful of unlabeled buttons on a piece of perfboard.

Of course, the presentation of this receiver isn’t really the point; it’s more of a proof of concept. You see, [Ricardo] is the person who’s actually developed the library that allows you to control the Si4735 from your microcontroller of choice over I2C. He’s currently tested it with several members of the official (and not so official) Arduino family, as well as the ESP32.

The documentation [Ricardo] has put together for his MIT licensed Arduino Si4735 library is nothing short of phenomenal. Seriously, if all open source projects were documented even half as well as this one is, we’d all be a few notches closer to world peace. Even if you aren’t terribly interested in adding shortwave radio reception to your next project, you’ve got to browse his documentation just to see where the high water mark is.

We actually first heard about this library a few days ago when we covered another receiver using the Si4735 and [Ricardo] popped into the comments to share some of the work he’d been doing to push the state-of-the-art forward for this promising chip.

Dealing with an antenna is one of those topics we never feel like we know enough about. MIT had a live stream of [Dr. Kiersten Kerby-Patel] discussing antennas in a talk, sponsored by the ham radio club on campus. You can see the recording below.

The main assertion of the presentation is that everything is a dipole unless it is a loop. Although the professor probably deals with antennas at an extremely high theoretical level, she did a great job of keeping it aimed at ham radio operators.

The talk is about an hour long, so it isn’t optimized for the YouTube generation. There’s some introductory material that looks as though it would have been in one of our old physics classes. However, the talk gets more practical towards the end.

There’s the obligatory mention of Yagis and loops. There’s even a Smith chart. If you don’t know what the Chu limit is, you should definitely be watching this video. The end of the talk covers some very small antennas using active devices or even moving parts.

If you want more discussions on the why behind antennas, we really liked this video. This two-parter is worth your time, too.