Category Archives: Amateur Radio

Ham Radio Podcasts

I’ve been meaning to do a quick post about podcasts that I listen to that are related to ham radio, just in case there are some among you who may not have heard about them, or who may have heard about them but haven’t given them a try. Here’s a list of what I listen to, along with what I like about them:

  • Soldersmoke: This podcast was recommended to me a couple of years ago by the staff at Ham Radio Outlet, and I’ve been an avid listener ever since. It’s the work of Bill Meara, N2CQR, who works for the State Department and enjoys radio as he moves around the globe. I’ve followed the podcast from London, to Italy, and now back to the States. Bill is interested in homebrew and QRP operation, and the topics generally reflect that. It’s mostly a one person affair, but Bill is a good speaker and engaging. He’s also written a book which you can get on Lulu and Kindle, detailing his adventures in radio. Despite the focus on homebrew and QRP, sometimes it drifts a bit into debugging computer equipment, travel and a fair amount of promoting his book, which may or may not bug you: check it out for yourself. I still eagerly await each episode.
  • The ICQ Podcast: This is a great ham radio podcast, produced by Martin Butler, M1MRB and his son Colin, M6BOY. The format is usually a brief introduction, followed by news stories read by Colin and Martin, and then usually followed by a feature topic which Martin presents, sometimes with guests. Recently they have begun to add new content, including guest reporting and propagation reports. If you are just interested in ham radio news, this is a good podcast. What I really enjoy about the podcast is the honest enthusiasm they have for simply playing around with radios. While they are living in the UK, their news segments cover stories from Europe, the U.S. and Australia pretty regularly. The technical content isn’t super high, but I enjoy it.
  • Ham Nation: A brand new podcast, as of this writing only two episodes exist, and I’ve only listened to one. Legendary ham and manufacturer of microphones Bob Heil is the host of this hour long program. In the first show, Bob was joined by musician Joe Walsh, WB6ACU and Dave Jennings WJ6W, and talked (for my tastes, somewhat vaguely) about the nominal topic of “The History of Ham Radio”, but really just talked about the history of Heil, Walsh and Jennings. It is being produced by Leo Laport’s TWiT network, and promises to be an interesting show with lots of good guests. On my commute today, I’ll listen to episode 2 on emergency communications, which has Gordon West as a guest. Keep an eye on this one.

Are there any others that people enjoy? Feel free to add them in comments below.

Dino Segovis builds a copy of Bell’s Photophone

Maker Dino Segovis has a website called hackaweek.com where he tries to do a hack a week, streaming his construction via uStream, and then posting youtube video and details on his blog. This week, he decided to build a copy of Alexander Graham Bell’s PhotoPhone in celebration of the 131st anniversary of its unveiling to the public.

I must admit though: I am not quite certain how it achieves modulation. Here’s my boggle: the solar cell produces a changing voltage in response to changes in the total number of photons which hit the cell. In Dino’s video, the solar cell is much smaller than the sun’s reflection (the reflection is five or six diameters). If the amplitude of the movement of the reflected disk is just a diameter or two (as it appears to be in the video) the solar cell would appear to be constantly illuminated, and there should be no change in the voltage produced.

But it obviously works, so there must be something else going on.

If there was a variation the brightness of the overall pattern from center to edge, then its movement would cause an amplitude variation. But what is the source of this variation? Defects in the mirror? Mirror curvature? Changes in the brightness of the sun disk from center to edge? Those variations all seem to be pretty small.

I’ve seen music transferred by the bouncing of a laser beam onto a solar cell, and that confused me as well.

Something to think about (and maybe build) once I get my laser diode modules from Deal Extreme.

FUNcube Dongle on order!

Huzzah! I’ve been wanting to get a Funcube Dongle Pro for some time, but they have been in short supply. Today, a fresh batch went on order, and this time: success!!

The Funcube Dongle Pro is a cool little software defined radio that plugs a USB port, and receives from 64Mhz to 1700Mhz. I am most interested in using it as a proper NOAA satellite receiver, but I have other applications in mind as well. Stay tuned for a review in the future when I get it in my hot grubby hands.

FUNcube Dongle | A radio that’s out of this world!.

More light transmitter experimentation…

Today, I had to do some yardwork, so I dusted off the weed whacker, and climbed the back of the hill to chop down some high grass. At the end of an hour, I was about 40% done (I’ll do the rest next weekend) but sneezing and coughing from the liberated pollen and dust. So, I called it a day, made a mental note to get a dust mask for next week, and showered.

But while I was chopping grass, I located an old solar powered LED light that had been lost among the tall grass. It was probably three or four years old, and covered in dirt and dust. The solar cell in particular looked like some water had gotten in it.

The perfect organ donor for an improved receiver for my LED transmitter, thought I.

And it is. I disassembled the light, snipped the LED panel out, and soldered it in place of the LED that I was using in place of my receiver previously. And, not surprisingly, it works better. A lot better! A lot louder. Over a greater distance. There is no real contest.

I tried to shoot some video of it, but my hands are simply too shakey (muscles twitching from operating vibrating machinery for an hour) and it’s unwatchable. But here’s a little MP3 file that will perhaps hint at some of the improvement.

Demonstration of solar cell as light receiver (MP3)

Addendum: I decided to go ahead and post some video. It’s still pretty shaky, but it’s a reasonable demonstration of what’s possible with a scavenged solar cell. Pardon for the relatively poor lighting: my office is lit by compact flourescent bulbs, and when they were all on, the 60 hz whine (which you can still hear despite lowering the light levels) was pretty irritating.

KA7OEI – LED Linear Current Modulator

My silly experiment with an LED communicator naturally led me to looking up more complex (and better engineered) versions of the same kind of circuit. There are now cheap LEDs that can emit a watt or more of energy, and produce a prodigious amount of light. It seems like an area which is ripe for amateur experimentation (and just general mucking around) and could leverage some of my optical design skills as well. KA7OEI has some really good ideas and circuits for driving these kind of LEDs with as little distortion as possible, and will be definitely worth looking at:

KA7OEI – LED Linear Current Modulator.

Update re: the HamCan.

Dave, NM0S and designer of the HamCan, a kit that I previously assembled, but had some difficulty with nicely contacted me via email today so ask if he could be of help. I’m pretty sure that whatever the issue is, it’s my own fault, but hopefully with some patient help from Dave I can figure it out over the next week or so if I can find some time to be in the workshop. It was darned nice of him to drop me an email with an offer of help.

Inductive Spikes: Simulation and Reality

Kindred spirits Atdiy and whisk0r over at the tymkrs blog were playing around with inductors:



They demonstrated that inductors can generative large inductive spikes: in spite of the fact that there coil is charged by a relatively low voltage, when you sharply disconnect a coil from a charging voltage, it generates a large voltage spike that can be measured (by a volt meter) and also generates a visible spark.

I thought it would be fun to see if I could simulate this using LTSpice. I wanted to make sure I understood what was going on, and try to see if I could get some measure of what voltages could actually be generated.

Here’s the schematic I came up with in LTSpice:

It’s a pretty simple schematic really. It’s got an inductor L1, that is about 450uH of inductance (calculated with an online calculator from rough measurements that Atdiy supplied me). The resistor in parallel is 10 megohm, which is similar to the impedance of a typical volt meter. I then have a voltage controlled switch, powered by a square wave. Whenever the input voltage goes greater than 0.5 volts, the switch connects, presenting a resistance of merely 1 ohm. When it drops below 0.5 volts, it presents a resistance of 10 megohms. The inductor is charged by a nominal 3.6 volt battery.

So, what does it look like when you simulate it?

Across the top, you can see the voltage that gets applied to the voltage controlled switch. Across the back, you see large negative spikes in voltage. Really large. We see spikes of nearly 7 megavolts. Pretty amazing, from a 3.6 volt supply! This simulation may be overly optimistic: after all, it doesn’t take into account the stray resistance and capacitance that are likely to be present. But clearly Atdiy’s real life test indicates that high voltages are being developed.

In real life applications where inductive loads might be connected and disconnected quickly to varying loads, it’s common to use diodes to protect the remaining circuit from these high voltage spikes. We can do that in our simulated circuits too. Let’s add a pair of diodes to shunt both positive and negative voltages to zero (I picked 1N4158 diodes, somewhat arbitrarily):

They do their job, check out the voltages:

Neat!

Simulating the Joule Thief with LTSpice

I always think it is good to follow up a practical build of an electronic circuit with some simulation to try to learn some of the underlying design principles. LTSpice is a great circuit capture/simulation system which runs on Windows, but also runs pretty well under Wine. I was a bit intrigued by the behavior I noticed in my video: while the LED lit quite well using a single AA battery with a nominal 1.5 volts, when I connected the circuit to an old, partially depleted lithium coin cell that I extracted from a burned out “throwie”, it did not light my LED despite being measured at a nominal 1.4v or so. I thought this was pretty interesting. I had an idea about what the problem was, so I thought I’d test it in LTSpice.

Warning: I don’t know what I’m doing. That’s why I am doing what I am doing.

Here’s the schematic that I entered:

I determined the value of the inductors (44uH) using an online toroid calculator, specifying an FT-50-43 toroid with 10 turns through it. The K1 statement creates a transformer out of L1 and L2, with a coupling coefficient of 0.99 (just a guess, they are wound on the same toroid, I expect it to work rather well). In the circuit as presented, the battery is represented by the voltage source V1 and the resistor labelled ESR. From a data sheet for EverReady AA batteries, I found that the typical series resistance is somewhere between 150 and 300 milliohms. I picked an LED out of LTSpice’s catalog: no attempt was made to ensure it was close to the random LED I grabbed from my junkbox.

If you simulate it for a half a millisecond, and look at the voltage at Vout, you get the following graph:

If you change the ESR to 30 ohms, and look at the voltage

Here’s a graph comparing them:

We can see that the voltage going into the LED peaks much higher, and remains higher for a significant period longer when supplied with a battery with a lower ESR. Using the FFT function, we can determine that the fundamental frequency is around 64Kh, and we can see that the average current is around 35 ma (a bit higher than the recommended average power for the LED, but not tremendously high, given the high frequency at which it operates).

When we have a 30 ohm resistance, the average current through the LED drops to a mere 3.5ma. While the voltage does appear to peak higher than the forward voltage needed to light the LED, the current supplied is simply too short and too low to significantly light the LED.

This seems to verify my experiments to a degree. But last night, I thought of this, and thought that perhaps I could boost the ability of these coin cells by paralleling them with a capacitor. I yanked out an electrolytic of around 220uF from my junk box, and wired it in parallel with the coin cell. The LED did light, but at a very low frequency, just a couple of Hertz. If I add a similar cap to my simulation, I don’t get this behavior. Not sure what’s going on. Any real engineers in the audience care to school me onwhy what I did here is completely inaccurate/wrong/stupid?

The Joule Thief — Lighting an LED with 1.5 volts

I was bored, but not quite up to the challenge of debugging my existing radio project, or starting a new one. I idly began winding some wire onto a FT-37-43 toroid, and then remembered that I had never constructed a “Joule Thief”, a simple little circuit that allows you to light an LED using just a 1.5 volt cell.

YouTube – The Joule Thief — Lighting an LED with 1.5 volts.

Addendum: I mentioned that legendary hacker Jeri Ellsworth had mentioned this circuit in one of her videos: I dug around and found the video. Her circuit is nearly identical, but adds a few components to implement a simple charging circuit.

I also did some experimentation with LTSpice to figure out why the lithium coin cells I scrounged from our old “throwies” didn’t light the circuit, even though they still measured 1.5v. It appears that these coin cells might have significant series resistance (perhaps as much as 30 ohms) compared to the much lower value for alkaline batteries (a nominal 150 to 300 milliohms, according to one datasheet I found). This appears to keep the transistor from supplying sufficient current to switch. I experimented with placing a capacitor across the coin cell (various values, from 33uF to 220uF electrolytics) and found that this did cause the LEDs to blink, but at a very low rate (with a 220uF, about 1Hz). I’ll try to follow up this post with one showing LTSpice and its simulation.

Ugly is Better

So, over the weekend I assembled the HamCan, and got some pretty wonky performance. I’m going to go through it all again and see if I can figure out why the receive performance is so bizarre, (loose connection? poor adjustment?) but it got me thinking that part of the issue is that typical PCB construction doesn’t really offer much advantage for prototyping. The boards are small. They don’t allow much room for experimentation, substitution and even debugging. My early experiments with so-called “ugly construction” like what I used for the FM transmitter I built last month worked much better. The technique is not optimized for mass production, but for individual experimentation and easy substitution and testing. That seems to be a very good thing.

So, my intention is to start an “Ugly Weekender”: one of Wes Hayward’s classic QRP designs. I’ve got a box set aside where I can start putting out the components I need (I should have most of them already, some of the variable caps might require a bit of substitution or creativity). But rather than just diving in, I think I am going to try to plan out the layout of each of the two/three boards it will cover, and consider modeling portions of the design in LTSpice. I’ll try to cover each step of this construction with videos and additional files that might be of use for someone considering a similar homebrew project. I’m in no hurry to get this done: it’s a project which is designed to maximize my own learning and enjoyment, so be patient (and encouraging, it really does help).

In the mean time, here are a couple of YouTube videos that serve as inspiration for this project.

Addendum: The original Ugly Weekender transmitter appeared in the August 1981 issue of QST in an article by Roger Hayward and Wes Hayward. The receiver appeared in the June 1992 issue in an article by Roger Hayward. Both are available to ARRL members through their excellent online archive of QST backissues.

Today’s Project: The HamCan

I ordered a little HamCan kit about a week ago. It’s a little QRP CW transceiver produced by the Four State QRP kit. Today, I spent about an hour assembling it, and fired it up. This is just a short status report: it’s acting a bit wonky. The tone sounds pretty rough, the frequency seems off, and adjusting the regeneration doesn’t seem to change anything. I’ll be debugging it over the next week or so, but consider this a quick little intro to it.

Addendum: Here’s the radio hooked up and “working”. If anyone has any bright ideas on how to debug it, feel free to drop me an email with your suggestions.



Eldon made a very cool version of the FM micro transmitter

Eldon, WA0UWH was inspired by my recent experiment with Tatsuo Kogawa’s micro transmitter, and decided to build his own. Unlike my rather crude (but surprisingly effective) lashup on some copper clad board, Eldon designed a tiny 0.5″x0.8″ board, etched it and used surface mount components to finish it. Very nifty, and totally dwarfed by the 9v battery that powers it. Check it out!