am radio

33 Articles

1940s Portable Radio Is A Suitcase

August 13, 2019 by 12 Comments

The meaning of the word portable has changed a bit over the years. These days something has to be pretty tiny to be considered truly portable, but in the 1940s, anything with a handle on it that you could lift with one hand might be counted as portable electronics. Zenith made a line of portable radios that were similar to their famous Transoceanic line but smaller, lighter, and only receiving AM to reduce their size and weight compared to their big brothers. If you want to see what passed for portable in those days, have a look at [Jeff Tranter’s] video (below) of a 6G601 — or maybe it is a GG601 as it says on the video page. But we think it is really a 6G601 which is a proper Zenith model number.

According to [Jeff], 225,350 of these radios were made, and you can see that it closes up like a suitcase. The initial 6 in the model number indicates there are 6 tubes and the G tells you that it can run with AC or batteries.

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The Power Of Directional Antennas

July 3, 2019 by 32 Comments

AM broadcasting had a big problem, but usually only at night. During the day the AM signals had limited range, but at night they could travel across the country. With simple wire antennas, any two stations on the same frequency would interfere with each other. Because of this, the FCC required most radio stations to shut down or reduce power at night leaving just a handful of “clear channel” stations for nighttime programming. However, creating directional antennas allowed more stations to share channels and that’s the subject of a recent post by [John Schneider].

When it comes to antennas, ham radio operators often think bigger is better. After all, hams typically want to work stations far away, not some specific location. That’s not true in the commercial world, though. The big breakthrough that led to, for example, cell phones was the realization that making smaller antennas with lower power at higher frequencies would allow for reuse of channels. In those areas the focus is on making cells smaller and smaller to accommodate more people. You can think of AM broadcasting as using the same idea, except with relatively large cells.

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A Modern Take On The Crystal Radio

January 19, 2018 by 20 Comments

We’ll admit that [3DSage] has a pretty standard design for a crystal radio. What we liked, though, was the 3D printed chassis with solderless connections. Of course, the working pieces aren’t 3D printed — you need an earphone, a diode, and some wire too. You can see the build and the finished product in the video below.

Winding the coil is going to take awhile, and the tuning is done with the coil and capacitance built into the tuning arrangement so you won’t have to find a variable capacitor for this build. There is a picture of the radio using a razor blade point contact with a pencil lead, so if you want to really scrimp on the diode, that works too, and you can see how at the end of the video.

We did like the use of cord ends from a sewing and craft supply store to serve as solderless springs. This would be a great item to print off a few dozen copies and use it for a school or youth group activity. You might want to pair it with an AM transmitter, though so the kids won’t be dismayed at what is playing on AM in most markets. [3DSage] uses a sink for ground — literally a kitchen sink. However, if you try this, make sure all the pipes are metal or you won’t get a good ground and you probably won’t pick up any stations.

We’d like to get some of those springs and make some other kind of starter projects with them like the kits many of us had as kids. This reminded us of the old foxhole radios, found during World War II.

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Dust Off Those AM Radios, There’s Something Good On!

January 12, 2018 by 53 Comments

If you are into vintage electronics or restoring antique radio equipment you may be very disappointed with the content offerings on AM broadcast radio these days. Fortunately there is a way to get around this: build your own short-range AM broadcast station and transmit curated content to your radios (and possibly your neighbors). There are several options for creating your own short-range AM broadcast station, and this gives you something fun to tune into with your vintage radio gear.

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Data Exfiltration With Broadcast Radio And CD-ROM Drives

July 5, 2016 by 78 Comments

The first music played on personal computers didn’t come out of fancy audio cards, or even a DAC. the first audio system in a personal computer was simply holding an AM radio up to the case and blinking address pins furiously. This worked wonderfully for homebrew computers where EMC compliance hadn’t even become an afterthought, but the technique still works today. [Chris] is playing music on the radio by sending bits over the system bus without using any wires at all.

[Chris]’ code is based on the earlier work of [fulldecent], and works pretty much the same. To play a sound over the radio, the code simply writes to a location in memory when the waveform should be high, and doesn’t when the waveform is low.

Of course the ability to exfiltrate information over an airgap has a few more nefarious purposes, but [Chris] also has another way of doing just that which is undefeatable by a TEMPEST shielded computer. He can send one bit at a time by opening and closing a CD-ROM drive, capturing these bits with a webcam. Is it useful? It’s hard to imagine how this setup could ever capture any valuable data, but it is a proof of concept.

AM, The Original Speech Transmission Mode

June 7, 2016 by 58 Comments

Here’s a question: when did you last listen to an AM radio station? If your answer is “recently”, chances are you are in the minority.

You might ask: why should you listen to AM? And you’d have a point, after all FM, digital, online, and satellite stations offer much higher quality audio, stereo, and meta information, and can now be received almost anywhere. Even digital receivers are pretty cheap now, and it’s by no means uncommon for them to not even feature the AM broadcast band at all. Certainly this has driven an exodus of listeners to the extent that AM radio has been in slow decline for decades, indeed it’s disappearing completely in some European countries.

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Heathkit’s Triumphant Return?

December 17, 2015 by 46 Comments

Heathkit, the storied purveyor of high-quality DIY electronics kits that inspired a generation of enthusiasts and launched the careers of many engineers, has returned from the dead. We think. At least it seems that way from this build log by [Spritle], an early adopter of the rebooted company’s first offering. But if [Spritle]’s experience is any indication, Heathkit has a long way to go to recreating its glory days. Continue reading “Heathkit’s Triumphant Return?” →