Ripples in the Ether

NT7S CPO

Here it is, a completed version of the simple discrete component code practice oscillator that I promised. I tweaked the circuit just a little bit and made a Manhattan layout that will enable the CPO, a 9 volt battery, and all of the required controls to fit into a standard sized Altoids tin. This CPO produces a nice sine wave at about 600 Hz, unlike many of the other CPOs that output a buzzy square wave tone. There are no exotic parts used in this project, only a couple of generic NPN transistors, a handful of common resistors and capacitors, and a trim pot. The output level is sufficent for headphone use, although it will not blow your eardrums out, even at full volume. If you need to use a speaker with this oscillator, just plug it into a set of amplified speakers, like those used for a computer. This project would also make a good oscillator for CW practice on a VHF/UHF FM repeater. The volume control should allow you to adjust the output level to one that is appropriate for the microphone jack of a FM rig.

Inside view of the CPO

I’ve attached a PDF schematic and layout diagram below. I haven’t created any build instructions, but it should be an easy build for anyone who has any experience with Manhattan construction. Let me know if you plan on using this design for a group build to help people learn CW, I might be able to work with you to create such a document. Print out the layout diagram at 100% scale, and you should be able to use it to size your copper clad board and mark the locations of your pads. I hope this is helpful to you and can help you to introduce new operators to CW.

Files

• NT7S Code Practice Oscillator
• NT7S Code Practice Oscillator Layout Diagram
• NT7S Code Practice Oscillator BOM

Handmade Art Radios

You have to feast your eyes on these wonderful works of art. This gentleman makes gorgeous, functional tube and crystal radios as works of art. He apparently also sells some of the pieces, and considering how nice they are, the prices seem very reasonable. I guess you could say that this is the anti-ugly construction. Very inspiring!

Via the Make Magazine blog

Sorry for the lack of updates this week, I’ve been under the weather and haven’t accomplished anything other than dragging my sorry carcass to work. And that was a struggle. Anyway, I found something that might interest you math and computer geeks out there. This website, called Project Euler, presents a series of mathematical challenges to overcome. The unique thing about these problems is that they are geared to be solved with the aid of a computer program. You can write your program in any language of your choice. For example you could choose BASIC, C, assembler, or in my case, Python. I’ve wanted to learn Python but never really had a good excuse to try it yet. This will give me a chance to get familiar with the syntax while having a bit of fun at the same time (if your idea of fun is trying to solve math problems, that is). If you create an account on the site, you can track your progress, and as you solve each problem, a forum for that solution is unlocked. Nothing earthshattering, but a bit of a fun diversion for true geeks like me.

VK6DI spot of NT7S

Today is our housewarming party, so that means chores, chores, and more chores for me. I figured I could still have a little ham radio fun by firing up WSPR and letting it run while I took care of stuff around the house. I didn’t really expect it, but my little 1 watt signal to the random wire is managing to haul itself to nearly the other side of the globe this morning. Both VK6DI and VK2AWD have been receiving my signal fairly reliably. I was hoping that I could hear a VK station here in Beaverton, but it doesn’t appear that either of those two are set up to transmit. Regardless, it’s still really gratifying to see your modest signal make such a spectacular trip.

NT7S Spotted

Here’s a screen grab of the latest spots of me uploaded to the spotting page. I’m hoping to run my WSPR beacon a bit more over the next few months at various times of the day to try to get a better picture of what propagation is like at my QTH. I’ve been so constrained in my HF operations in the past, I’ve never really been able to count on working any DX and I have no grasp of what the propagation characteristics are like (other than the generic characteristics of each band). Neat stuff for sure, and I would like to try other bands. However, I think I’m going to stay off 40 meters until the agreed-upon frequency is changed. Right now the WSPR watering hole on 40 meters is just about smack dab on the QRP frequency, much to the chagrin of a few QRPers. I can’t say that I blame them, I don’t think that was the wisest choice. A lost of WSPR participants run 5 watts, so it’s not like these are microwatt beacons we are talking about. In the mean time, I’ll continue to have fun on the other bands.

Someone’s getting a bit greedy.

This is a reply that I wrote in response to a thread on the “old” QRP-L regarding the dying of ham radio in the US. The post that I was replying to lamented the instant gratification culture that we have developed in the country. I felt that I should stick my reply here on the blog as well.

I believe that it’s true that the addiction to instant gratification in American culture is a huge contributor to the problems with getting younger folks interested in ham radio (the other major factor being the stinky, unkempt, loudmouth curmudgeon contingent). However, with the huge economic challenges facing the USA, I truly believe that we will have to abandon this type of lifestyle and return to some semblance of thrift, frugality, and ingenuity. Instant gratification is going to mostly die, by financial necessity. I don’t think most families will have the resources to just buy the kids a new $500 game system every two years and a new $60 game every month. Nor will many of us be able to afford a lot of the other luxuries that we are accustomed to, such as the $150/mo cable package, dining out most days of the week, and purchasing a lot of the frivolous trinkets that we think we need that actually end up gathering dust in the corner of the garage.

As QRPers, we are uniquely poised to take positive advantage of this situation. We are used to making the most out of the least. We are the weirdos who like to scrounge for junk and salvage components from the cast-off electronics that others have trashed. We can take a handful of cheap parts and turn it into hours and hours of entertainment, as well as education. We are already seeing some of this mentality take root in the “Maker” movement, so there’s potential to rekindle some of the radio magic with the younger generations. The standard ARRL path of getting a kid to take the Technician test and giving them an HT is a dead end. Not many kids are going to be interested in 2 m/70 cm repeater operations. We can’t treat young people like they are too stupid or simple-minded to do anything more than yak on a repeater. They need to be challenged, and our particular slice of the hobby can challenge them.

There’s not going to be any grand, centralized, ARRL-type movement that’s going to change things. We each have to make sure that we live up to the standards that will present the best face for ham radio and homebrewing. Do your part, whether it is through Elmering, evangelizing the hobby in a positive way, designing kits for new hams, taking part in the Maker movement, talking to the media, or anything that uses your strengths to advance the art and science of the hobby. As times get more difficult, keep a positive outlook on things. People will look for outlets from the lousy times, and we have the opportunity to offer them an outlet with a unique combination of fun and learning.

This last weekend Jennifer left town for a business trip, so Baxter and I are currently own our own as bachelors. So I got the chance to participate in the monthly SKCC Weekend Sprint without too many interruptions and “honey do” items. Last month was my first try at WES, and I pretty much just dipped my toes in the water, with a total of 6 QSOs. This time, I felt a bit more comfortable and had more time to devote to the sprint (not that WES is a stressful event, on the contrary, it is very laid back). On this attempt, I turned the IC-718 down to 5 watts and went true QRP. Overall, I had a much better showing than last time. 16 total QSOs, 9 S/P/C, but only 60 bonus points. According to the theme of this sprint, bonus points were given for DX contacts, contacts with non-Centurion and non-Tribune members, and contacts with the club call. I tried a few times to work the two DX stations that I heard on 15 meters (just barely), but they never heard me. I also struck out when trying to contact the club call. Still, I had a blast this time as I got more comfortable with the event and with my CW skills. I’m not a contester, but this is a really enjoyable event, and I would recommend it to anyone who likes to use a straight key. I also found out that 15 meters seems to be a bit more open than I even suspected right now. Next time, my goal is to break 20 QSOs and up my score a bit more. I hope to work you in the next WES!

Baxter Is Uncertain

I finally got a few days of decent sleep (decent meaning more than 4 hours), so I had a little energy to work on the simple DC transceiver. A few days ago, I got the remainder of the audio chain working. The emitter follower on one of the outputs of the differential mixer was yanked, and I connected a class-A audio amp directly to the mixer. Then I stuck the emitter follower on the output of the class-A amp to enable the receiver to drive low-impedance headphones. No, it’s not extremely efficient, but it is simple and it works. Best of all, no transformers are needed. As an afterthought, I added a simple shunt-to-ground mute circuit with a 2N7000. That might have to be tweaked a bit later

Unnamed on the Bench

The transmitter is also a simple design. The second output of the differential mixer is tapped with an emitter follower that will have its V_CC line keyed to control transmit. Directly following this is a 2N7000 class-C PA. After a bit of work tweaking the impedance matches to get the right amount of drive to the PA, I can easily get 2 watts out of the amp (before low-pass filtering). What’s neat is that the emitter follower puts out about +10 dBm, and it gets amplified up to +33 dBm in one stage. A very compact design that can generate a decent amount of power.

So in order to make this a true transceiver, I have a few things left to do. First thing, of course, is to get a low-pass filter on the transmitter. I’ll also need to provide a keying circuit and T/R switching. I’m still not sure what I’m going to do about a sidetone. I also think that I’ll put an RIT circuit in there and not worry about a fixed transmit offset (that would be very hard to get right in such a simple transceiver). Keep watching for another update, hopefully soon.

Hellschreiber Clock Display

I don’t know if the guy who created this is a ham (he does say he’s an engineer), but it’s a neat application of some old-school technology. He uses a PIC 12F510 to output a Hellschreiber modulated square wave right to his PC’s sound card line in port. I really get a kick out of seeing one of these “obscure” ham technologies escaping out into the Maker universe. The hardware is dead simple, as you can see in the instructions. If you wanted to try to create a Hellschreiber beacon, I don’t see why you couldn’t just take this same design and plug it into your rig’s sound card interface instead of a PC. I’m already thinking about how cool this would be to try…there’s a good chance I will give it a shot (with an AVR) after I finish up my latest DC transceiver. Watch out for more aliens infecting the bands.

Unnamed Simple Discrete 80 Meter Rig

Yes, its a post about another simple, low-performing direct conversion receiver. However, I think that this one is slightly unique. I was inspired to give this a try based on the Flea minimalist transceiver that was introduced on the EMRFD Yahoo group. These little rigs are fun to build in an evening, but just how usable are they? Would you feel comfortable giving it to a new ham and believing that they even had a small chance of success? For me, these Pixie-class rigs are nearly unusable due to the horrible AM broadcast interference that blows right through the rig. While a minimalist rig is an admirable thing, they are only useful in limited circumstances. I figure that a few things have to be added to these rigs in order to make them more than a novelty. KD1JV also shares this viewpoint, and has created his own answer to the Pixie.

I’ve started with a similar philosophy, but built the rig around a different topology. The basic strategy is to use a differential amplifier as an active mixer. The rig is designed for the 80 meter band, which is probably the easiest for homebrewing. The LO is a Colpitts ceramic resonator oscillator, but is not separate from the mixer. Instead, the oscillator is built around the third transistor which acts as the constant current source. I know that this is certainly not a new idea; it’s used all of the time in NE602-based QRP circuits. However, I don’t think this topology is seen very much in discrete component use. It saves quite a bit of circuit space and is composed of very common components.

The rest of the receiver is very simple. I placed a standard double-tuned circuit bandpass filter in front of the RF port of the mixer to filter out all of the AM BCB crud. The output of the mixer feeds a dirt-simple emitter follower to transform the relatively high collector impedance of the diff amp mixer to a low impedance output. I haven’t designed the final AF amp yet, but I don’t think it will take much to get the signal up to headphone levels. When the emitter follower output is connected to my test bench AF amp, I have to have the amplifier AF gain control turned nearly all the way down, lest the whole thing start oscillating wildly.

Tonight, I connected the RX to the bench AF amp and the antenna to see how it would work. Tonight was an excellent night to try, since we are right in the middle of Sweepstakes. Pleasantly, the receiver immediately came to life with a cacophany of CW signals in the unfiltered audio output of the receiver. I’ve attached a recording of the receiver output so that you can get a feel for how well it works for such a minimalistic design. The ceramic resonator osc tunes from nearly 3.500 MHz to 3.580 MHz, and I tune across the entire band in this clip.

All I have to do to finish the receiver is to add on a discrete component AF amp. I think that a single class-A stage of amplification will be enough to get the audio up to headphones level. After that, I’m going to try to tack on a transmitter by picking the VFO signal off of the other unused collector port of the diff amp. I think that I can get away with another emitter follower as a buffer, followed by a class-C PA. I’m shooting for around 1 watt of output power, which is enough to snag QSOs without too much difficulty. I think this could be a lot of fun to build as a kit. It’s will be quite a bit more complex than a Pixie or Flea, but also quite a bit more usable. Stay tuned for further developments on this rig.