Ask Hackaday: Has anyone built a radio telescope?

[Michael] sent in a question regarding the latest advances in software defined radios available for $20 on eBay:

I’ve been looking in to SDR lately, mainly for the possibility of using it for incredibly cheap radio astronomy. So far all I’ve found are whispers. I’m 18 and have very little experience, but I figured you might be able to help me find a little more info.

This really brings me back, [Michael]. I saw Contact in the theater (surprisingly, a rare case when the book and movie are equals), and in my childish exuberance went out and listened to lightning on Jupiter. The financial difficulties of expanding my setup meant the experiments stopped there, but at least I knew amateur radio telescopy was possible.

The latest and greatest advance in software defined radio – namely, a $20 TV tuner dongle – brings something new to the table. Instead of the thousands of dollars in gear that was required in 1997 when I last looked into this, it’s possible to set up a  passable radio telescope for under $100.

I’ll leave it to the Hackaday commentors to fill [Michael] in on the details, but here’s my suggestion:

Optimize your setup for 1420 MHz. There are three reasons for this: firstly, very few things in the universe absorb radio waves at a frequency of 1420MHz; there’s a reason it’s so often used in radio astronomy. Secondly, most government agencies around the world ban (or at least don’t look too kindly upon) transmitting on 1420 MHz. This frequency has been somewhat protected for use by astronomers. Thirdly, most of the Realtek TV tuner dongles have a frequency range of 64 – 1700 MHz, so it’s possible to receive 1420 MHz with this minimal setup.

As far as antennas go, your best bet is probably going to be one of those old C-band parabolic antennas from the 80s. That will make your telescope highly directional and give it a huge amount of gain. There is the problem of having a 20-foot-wide eyesore in your back yard, however. Alternatively, you could use a smaller DirecTV satellite dish, but I’m not making any promises with that. It’ll work, but it’s too small for an optimal setup.

I’ll concede the floor to anyone who has additional information. If you’ve built a radio telescope, send it in and I’ll put it up.

Ask Hackaday: Troll Physics Super Deluxe Edition

Here’s a brain bender for you: YouTube user [Fredzislaw100] put up a video of six LEDs and six switches wired up in series. After soldering a resistor and 9V battery connector, the first switch turns on the first LED, the second switch turns on the second LED, and so on for the rest of the circuit.

We’ve seen this trick before from [Fredzislaw100], only this time he’s moved up from 3 LEDs to 6. In the reveal of the previous trick, [Fredzislaw] built two AC power supplies inside a nine volt battery connector; one high frequency and one low frequency. The low frequency AC line powers the first two LEDs with the help of diodes in the switches and LEDs. The high frequency AC line turns on the third LED with the help of an inductor inside an LED. Apparently [Fredzislaw] still has some soldering skills to show off; the circuit powering this trick is most likely the work of a soldering god.

From a close viewing, it looks like LEDs are wired up in pairs, i.e. LED 1 works the same as LED 2, LED 3 works the same as LED 4, etc. We’ll let Hackaday readers argue it out in the comments as to how this trick is possible.

Tip ‘o the hat to [Th0m4S] for sending this one in.

The pi pad

In the world of electronics we have impedance; the combination of all forces which oppose the flow of electric current. Often times we have circuits with different impedances, 50 ohms for RF, or 75 for cable TV. It’s pretty important to use the right coax in these circuits, else you’ll be wondering why your RG-58 antenna feed line doesn’t give you anything good to watch.

It’s pretty important to match impedances when connecting different circuits. Apart from the obvious flaws such as a 50 ohm load blowing up a 300 ohm amplifier, there are subtler things such as signal reflection and destructive interference which might just be enough to break whatever it is your playing with. RF mosfets are not cheap! But how could we match impedances? Well we could always use a transformer, but those are rather expensive and bulky. What if we only have a box of resistors to play with? [Read more...]

A bit about the diode

Most of you already know what a diode is, but how much do you really know about the device?

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Ask Hackaday: Building nano scale antennas

As an RF engineering student, [Camerin] is usually tasked with pointless yet educational endeavors by his advisor and professors. Most of the time (we hope) he sees the task through and ends up pulling something out of his hat, but a few days ago a professor dropped a bombshell on him. After reading this article on nano scale antenna fabrication, a professor asked [Camerin] if it was possible to build a 3D inkjet printer with a ludicrous amount of accuracy and precision.

The full article, Conformal Printing of Electrically Small Antennas on Three-Dimensional Surfaces, was recently published in Advanced Materials and is available via Google Scholar. The jist of the article is that three-dimensional antennas printed on a sphere approach the physical limits of how good an antenna can be. To test out these small, spherical antennas, the authors of the paper built an extremely high-precision 3D inkjet printer that draws antenna traces on a glass sphere with conductive ink.

The positional accuracy of this printer is 50 nanometers, or about half the size of an HIV virus. The conductive silver ink is delivered by a nozzle with a diameter of 100 to 30 µm and prints onto a glass sphere about 6 mm in diameter. This is a level of precision that companies and research institutions pay top dollar for, so we’re left wondering how the authors built this thing.

We’re turning this question over to the astute readers of Hackaday: how exactly would you build a 3D inkjet printer with this much accuracy and precision? Would it even need to be that precise? Post your answer in the comments.

Ask Hackaday: Did you catch the Grammys?

Although award shows aren’t necessarily our thing, [T. D.] sent in something that piqued our interest. His friends recently got back from the Grammy awards where they witnessed thousands of LED bracelets blinking in time to a performance by Coldplay. A little bit of YouTubing pulled up this video that demonstrates the effect (because that video will probably be taken down shortly, just pick something from this link).

[T.D.]‘s friends brought one of these bracelets back with them and like a good Hackaday reader, he cracked it open. This is the precious board pic that [T.D.] sent in. We’re pretty confident that the IC is an ATMega48PA, but beyond that we’re not quite sure how these bracelets can, “light up and flash at precisely the right time” as [T.D.] puts it.

From what we saw on the Grammy broadcast, it’s possible these bracelets merely flashed whenever the user clapped their hands. A circuit that simple doesn’t require a microcontroller, so we’re left wondering what the heck is going on here. If you’ve got an idea of how these choreographed light display bracelets work, drop a note in the comments.

EDIT: Commentors have pointed out these wristbands are called ‘Xylobands.’ There’s a great video of these wristbands in action at the 2011 X Factor finale.

Ask Hackaday: Troll physics edition

[Martin] sent in two videos he found while cruising the tubes. The first video is a simple circuit with a resistor, three switches, and three LEDs. All the components are soldered together right in front of the camera. When a battery is connected, turning the first switch on makes the first LED light up. Turning the second switch on makes the second LED light up, and the same thing goes for the third switch and LED. Obviously we’re dealing with powers that are incomprehensible with even several cups of coffee.

The second video features the same resistor/switches/LEDs, this time in a parallel circuit. Turning on the first switch makes the first LED light up, and the second switch makes the second LED light up. Truly we are dealing with an expert in troll physics.

This is probably something really benign and uninteresting, but it sure is enough to wake up enough brain cells on a Monday morning. We’re not going to hypothesize, so check out the comments where we expect the correct answer to be.

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