Turn Your Old-school CRT Into A YouTube Media Player

October 20, 2019 by Sharon Lin 40 Comments

Ever wish you could enjoy modern conveniences like YouTube in a retro world of CRTs and late 20th century graphics?

[Johannes Spreitzer] happened to find an old VIENNASTAR CRT (cathode-ray tube television) made by the Austrian brand Kapsh at a flea market. The CRT dates back to 1977 and uses just RF input, making it useless as a modern television set since most TV stations nowadays broadcast primarily in digital.

However, HDMI-to-RF transmitters do exist, making it possible to convert HDMI signals to RF or coaxial cable output to replace an antenna signal. What [Spreitzer] did next was to plug in a Chromcast and essentially convert the CRT into an old-school monitor. You can see some of the trippy graphics in the video below – the video samples shown fit the retro aesthetic, but I’m sure there’s video combinations that would seem pretty out of place.

HDMI-to-RF adapters are pretty easy to pick up at a hardware store, and they allow you to project videos onto specific channels on a CRT. Needless to say, they don’t work the other way around, although since there are still televisions that only pick up RF broadcasts, coaxial to HDMI adapters do exist.

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Fast Video Covers Coax Velocity Factor

October 11, 2019 by Al Williams 14 Comments

We once saw an interview test for C programmers that showed a structure with a few integer, floating point, and pointer fields. The question: How big is this structure? The correct answer was either “It depends,” or “sizeof(struct x).” The same could be said of the question “What is the speed of light?” The flip answer is 186,282 miles per second, or 299,792,458 metres per second. However, a better answer is “It depends on what it is traveling in.” [KB9VBR] discusses how different transmission lines have different velocity factors and what that means when making RF measurements. A cable with a 0.6 velocity factor sees radio signals move at 60% of that 186,282 number.

This might seem like pedantry, but the velocity factor makes a difference because it changes the actual measurements of such things as dipole legs and coax stubs. The guys make a makeshift time domain reflectometer using a signal generator and an oscilloscope.

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Raspberry Pi Ham Radio Remote Reviewed

October 7, 2019 by Al Williams 18 Comments

One problem with ham radio these days is that most hams live where you can’t put a big old antenna up due to city laws and homeowner covenants. If you’re just working local stations on VHF or UHF, that might not be a big problem. But for HF usage, using a low profile antenna is a big deal. However, most modern radios can operate remotely. Well-known ham radio company MFJ now has the RigPi Station Server and [Ham Radio DX] has an early version and did a review.

As the name implies, the box contains a Raspberry Pi. There’s also an audio interface. The idea is to consolidate rig control along with other station control (such as rotators) along with feeding audio back and forth to the radio. It also sends Morse code keying to the radio. The idea is that this box will put your radio on the network so that you operate it using a web browser on a PC or a mobile device.

According to MFJ, you can operate voice, Morse code, or digital modes easily and remotely. The box uses open source software that can control over 200 different radios and 30 rotors. Of course, you could build all this yourself and use the same open source software, but it is nicely packaged. [Ham Radio DX] says you don’t need to know much about the Pi or Linux to use the box, although clearly you can get into Linux and use the normal applications if you’re so inclined.

Even if you don’t want to transmit, we could see a set up like this being used for remote monitoring. We’d like to see a companion box for the remote end that had the audio hardware, a keyer, and perhaps a knob to act as a remote control of sorts. Of course, you could probably figure out how to do that yourself. We wonder if some ham clubs might start offering a remote radio via an interface like this — we’ve seen it done before, but not well.

Your $50 radio probably isn’t going to work with this, and if you use FT8, you could argue you don’t need to be there anyway.

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Bent Electric Field Explains Antenna Radiation

October 2, 2019 by Al Williams 15 Comments

We all use antennas for radios, cell phones, and WiFi. Understanding how they work, though, can take a lifetime of study. If you are rusty on the basic physics of why an antenna radiates, have a look at the very nice animations from [Learn Engineering] below.

The video starts with a little history. Then it talks about charges and the field around them. If the charge moves at a constant speed, it also has a constant electric field around it. However, if the charge accelerates or decelerates, the field has to change. But the field doesn’t change everywhere simultaneously.

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Bouncing Signals Off The Moon

October 1, 2019 by Al Williams 28 Comments

One of the great things about ham radio is that isn’t just one hobby. Some people like to chit chat, some like to work foreign countries, some prepare for emergencies, and there are several space-related activities. There are hundreds of different kinds of activities to choose from. Just one is moonbounce, and [Ham Radio DX] decided to replicate a feat many hams have done over the years: communicate with someone far away by bouncing signals from the moon.

The set up is pretty sophisticated but not as bad as you might imagine. You can see that they spend a lot of time getting the equipment aligned. A known reference point helps them set the position of the antenna. A GPS keeps both stations in sync for frequency and time.

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Take A Break From Arduinos, And Build A Radio Transmitter

September 30, 2019 by Al Williams 12 Comments

When you start watching [learnelectronic’s] two-part series about making a radio transmitter, you might not agree with some of his history lessons. After all, the origin of radio is a pretty controversial topic. Luckily, you don’t need to know who invented radio to enjoy it.

The first transmitter uses a canned oscillator, to which it applies AM modulation. Of course, those oscillators are usually not optimized for that service, but it sort of works. In part two he reduces the frequency to 1 MHz at which point it can be listened to on a standard AM radio, before adding an amplifier so any audio source can modulate the oscillator. There’s a lot of noise, but the audio is clearly there.

This is far from practical of course, but combined with a crystal radio it could make an awesome weekend project for a kid you want to hook on electronics. The idea that a few simple parts could send and receive audio is a pretty powerful thing. If you get ready to graduate to a better design, we have our collection.

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Probe The Galaxy On A Shoestring With This DIY Hydrogen-Line Telescope

September 29, 2019 by Dan Maloney 6 Comments

Foil-lined foam insulation board, scraps of lumber, and a paint-thinner can hardly sound like the tools of a radio astronomer. But when coupled with an SDR, a couple of amplifiers, and a fair amount of trial-and-error tweaking, it’s possible to build your own hydrogen-line radio telescope and use it to image the galaxy.

As the wonderfully named [ArtichokeHeartAttack] explains in the remarkably thorough project documentation, the characteristic 1420.4-MHz signal emitted when the spins of a hydrogen atom’s proton and electron flip relative to each other is a vital tool for exploring the universe. It lets you see not only where the hydrogen is, but which way it’s moving if you analyze the Doppler shift of the signal.

But to do any of this, you need a receiver, and that starts with a horn antenna to collect the weak signal. In collaboration with a former student, high school teacher [ArtichokeHeartAttack] built a pyramidal horn antenna of insulation board and foil tape. This collects RF signals and directs them to the waveguide, built from a rectangular paint thinner can with a quarter-wavelength stub antenna protruding into it. The signal from the antenna is then piped into an inexpensive low-noise amplifier (LNA) specifically designed for the hydrogen line, some preamps, a bandpass filter, and finally into an AirSpy SDR. GNURadio was used to build the spectrometer needed to determine the galactic rotation curve, or the speed of rotation of the Milky Way galaxy relative to distance from its center.

We’ve seen other budget H-line SDR receiver builds before, but this one sets itself apart by the quality of the documentation alone, not to mention the infectious spirit that it captures. Here’s hoping that it finds its way into a STEM lesson plan and shows some students what’s possible on a limited budget.