Ham Radio Public Service Activities – Rewarding And Useful

January 15, 2016 by Rud Merriam 19 Comments

“Hi! I’m Rud, Kilo Five Romeo Uniform Delta.” That’s me introducing myself at a ham meeting. Ham radio operators kid that we don’t have last names, we have call signs.

Becoming an Amateur Radio Operator (ARO), our more formal name, is not difficult and opens a world of interesting activities, including hacking. As with anything new, becoming actively involved with an existing club can be daunting. The other hams at a meeting are catching up with their buddies and often seem uninterested in the new guy standing nearby. Some groups will invite new members to stand and introduce themselves early in the meeting, which helps break the ice.

Regardless of how anyone else acts at the meeting there is one ham who is always looking for someone new – the ham who manages public service events, where amateur radio operators help establish communications for large public gatherings. These can be local bike rides, walks, or runs; I’ve even seen hams working an art show. In the nomenclature adopted since 9/11, these are “planned incidents” in contrast to “unplanned incidents” like hurricanes, tornadoes, forest fires, snow storms, and other natural or man made disasters. Working planned incidents is training for unplanned incidents when that need arises. The basic activities for AROs are the same.

Here in the Houston there are two very big events that enlist hundreds of hams. The big one in January is the Houston Marathon. The other large event is the Houston to Austin Multiple Sclerosis 150 (MS 150) mile bike ride in April. That event starts on Saturday morning, takes a break mid-way on Saturday evening, and finally wraps up late on Sunday evening. Starting in the fall there are warm-up events for the Marathon and in the late winter bike rides to prepare riders for the MS-150. There are also other marathons, Iron Man races, walks, runs, and races throughout the year. Wherever your are, there are probably events nearby and they can always make use of your radio capability.

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Decoding Data Hiding In Star Trek IV

January 13, 2016 by Adam Fabio 40 Comments

1986: The US and Russia signed arms agreements, Argentina won the world cup, and Star Trek IV: The Voyage Home hit the theaters. Trekkies and the general public alike enjoyed the film. Some astute hams though, noticed a strange phenomenon about halfway through the film. During a pivotal scene, Scotty attempts to beam Chekov and Uhura off the Enterprise, but has trouble with interference. The interference can be heard over the ubiquitous Star Trek comm link. To many it may sound like random radio noise. To the trained ear of a [Harold Price, NK6K] though, it sounded a heck of a lot like packet radio transmissions.

By 1989, the film was out on VHS and laser disc. With high quality audio available, [Harold] challenged his friend [Bob McGwier, N4HY] to decode the signal. [Bob] used the best computer he had available: His brain. He also had a bit of help from a Cray 2 supercomputer.

[Bob] didn’t own his own Cray 2 of course, this particular computer was property of the National Security Agency (NSA). He received permission to test Frequency Shift Keyed (FSK) decoder algorithms. Can you guess what his test dataset was?

The signal required a lot of cleanup: The original receiver was tuned 900 Hz below the transmission frequency. There also was a ton of noise. To make matters worse, Scotty kept speaking over the audio. Thankfully, AX.25 is a forgiving protocol. [Bob] persevered and was able to obtain some usable data. The signal turned out to be [Bill Harrigill, WA8ZCN] sending a Receive Ready (RR) packet to N6AEZ on 20 meters. An RR packet indicates that [Bill’s] station had received all previous packets and was ready for more. [Bob] called to [Bill], who was able to verify that it was probably him transmitting in the 1985 or 1986, around the time the sound editors would have been looking for effects.

That’s a pretty amazing accomplishment, especially considering it was 1989. Today, we carry supercomputers around in our pockets. The Cray 2 is roughly equivalent to an iPhone 4 in processing power. Modern laptop and desktop machines easily out class Seymour Cray’s machine. We also have software like GNU Radio, which is designed to decode data. Our challenge to you, the best readers in the world, is to replicate [Bob McGwier’s] work, and share your results.

FM 101 And Transmitter Build With Afroman

January 9, 2016 by Kristina Panos 18 Comments

One of our favorite purveyors of electronics knowledge is at it again. This time, [Afroman] explains how frequency modulation works while building up a short-range FM transmitter on a board he has available at OSH Park.

The design is based on a MAX2606 voltage-controlled oscillator (VCO) chip that can do 70-150MHz. [Afroman] sets it up to oscillate at about 100MHz using a 390nH inductor. He also put a potentiometer voltage divider on the 2606’s tuning pin. Voltage changes issued through the pot alter the transmitting frequency in small increments, making it easy to dial in a suitable channel for your broadcast. Add an electret mic and about a meter’s worth of solid-core wire and you have yourself an FM transmitter that is good for around 20 meters.

There are plenty of ways to build a small FM transmitter that allow for some experimentation and don’t involve placing SMD components. We covered a build last summer that uses a couple of 3904s and rides a 9V connector salvaged from a dead battery. The downside is that transistor-based transmitters tend to be less frequency-stable than a VCO chip.

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Free Cell Data Transfer With Slowest Morse Code Ever

January 6, 2016 by Mike Szczys 41 Comments

Readers of a certain age will remember the payphone trick of letting the phone ring once and then hanging up to get your quarter back. This technique was used with a pre-planned call time to let someone know you made it or you were okay without accruing the cost of a telephone call. As long as nobody answered you didn’t have to pay for the call, and that continues to be the case with some pay-per-minute cellphone plans.

This is the concept behind [Antonio Ospite’s] ringtone data transfer project called SaveMySugar. Don’t judge him, this work has been ongoing for around ten years and started back when cellphone minutes were a concern. We’re just excited to see that he got the excruciatingly slow thing to work.

Those wanting to dig down to the nitty-gritty of the protocol (and you should be one of them) will want to read through the main project page. The system works by dialing the cellphone, letting it ring once, then hanging up. The time between redials determines a Morse code dot, dash, or separation between characters. Because you can’t precisely determine how long it will take each connection to read, [Antonio] built ‘noise’ measurement into the system to normalize variations. The resulting data transfer works quite well. He was able to transfer the word “CODEX” in just six minutes and thirty seconds. But it is automatic, so what do you care? See the edge-of-your-seat-action play out in the video below.

If you can’t stomach that baud, here’s a faster Morse code data transmitter but it doesn’t use the phone.

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Get Your Amateur Radio License Already!

January 5, 2016 by Elliot Williams 81 Comments

We run a lot of posts on amateur radio here at Hackaday, and a majority of our writers and editors* are licensed hams. Why? Because playing around with radio electronics is fun, and because having a license makes a lot more experimentation legal. (*We’re sure you have good reasons for slacking, Szczys.)

So let’s say that you want to get your “ticket” (and you live in the USA). It’s easy: just study for an exam or two, and take them. How to study? We’re glad you asked, because we just found this incredibly long video that’ll prep you for the exam.

At six and a half hours, we’ll admit that we haven’t watched the whole thing, but what we did see looks great. Admittedly, we were a little bit unnerved by [John (KD65CY)]’s overdone enthusiasm. But the content is fundamental, broad-ranging, and relevant. Heck, even a bit entertaining.

Even if you’re not interested in taking the exam, but are just interested in some radio basics, it’s worth looking. If you give it a shot, and like what you see, let us know in the comments what times stamps you found interesting.

The other “secret” about the amateur radio exams is that all of the questions and their answers are drawn from a publicly available pool of questions. This means that you can just cram the right answers, pass the exam, and you’ll have your grey cells back good as new in no time. To help you along your path, here are all the current Technician questions with only the correct answer for each. (And here is the Python script that generated them.) Read through this, take a couple of practice exams, and you’ll be ready to go.

In our experience, the Technician exam is easy enough that it’s probably worth your while to study up for the General exam as well. You have to take the former before the latter, but there’s nothing stopping you from taking them all in one sitting. (General gets you a lot more international shortwave frequencies, so it’s at least worth a shot.)

But don’t let that slow you down. Just getting the Tech license is easily worth studying up for a couple of hours or so. You have no excuses now. Go do it!

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Art For Planespotters

December 31, 2015 by Elliot Williams 6 Comments

We don’t know art, but we know what we like. And this gizmo by [Johan Kanflo] is right up our alley.

First, [Johan] gutted an old Macintosh Classic computer and stuffed a Raspberry Pi inside. Now this is not really a new idea, but [Johan] did a very nice job with the monitor and his attention to detail shows in the rebuilt floppy-drive eject mechanism. He gives it back that characteristic “schlurp” noise.

Then he outfitted the Raspberry Pi with an RTL dongle running dump1090 software to listen to the ADS-B radio signals. The data extracted from the SDR is piped off to an MQTT server with all sorts of data about the airplanes overhead. Another script subscribes to the MQTT topic and figures out which is the closest and runs an image search for the plane type in question, publishing the results back to another MQTT topic. One final script subscribes to this last topic and displays the relevant images on the screen. Pshwew!

The end result is a Macintosh Classic that’s continually updated with whatever planes are closest to being overhead. We’re not at all sure if this is fine art, or part of the useful arts, or maybe even none of the above. But we really like the nice case job and think that using MQTT as a back-end for coordinating multiple concurrent Python scripts (on the same computer) is pretty cool.

You Can Learn A Lot From A Dummy (Load)

December 24, 2015 by Al Williams 53 Comments

If you work on RF circuits–even if you aren’t a ham radio operator–you ought to have a dummy load. A dummy load is a non-radiative “antenna” with known impedance that you can use to test your RF circuit without radiating. For radio work, you usually just need a 50-ohm resistor that is non-inductive (at least at the frequencies you are interested in) and that can dissipate the amount of power you’ll expect it to handle (at least for a short time). [VO1PWF] wanted a dummy load and built his own.
The Cantenna (not the Pringle’s kind; see right) was a famous dummy load design when Heathkit was in business. It was a single carbon rod immersed in a paint can full transformer oil (which we now know was full of dangerous PCBs; and we don’t mean printed circuit boards). [VO1PWF’s] design is a little more practical, using some resistors in parallel (20 1K resistors), a plastic pipe housing, and mineral oil to keep it all cool.

The reason for the parallel resistors is to maximize the power handling capability. The resistors are 3W units, so the dummy load–in theory–can handle 60 watts. Often, high power resistors are wire wound and thus have a good bit of parasitic inductance that makes the dummy load reactive (not a good thing since that makes the load impedance vary by frequency). They do make non-inductive wire wound resistors, but these aren’t truly non-inductive. The wire winds in two different directions, so the inductance tends to cancel out. We wouldn’t trust them to be a pure resistance in a high-power dummy load design.

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