All posts tagged DC20B

After my semi-success with the DC20B, I decided to tackle the Rock-Mite from Small Wonder Labs. I also got the Mighty Box. The kit is very small and has no toroids to wind. It does however have a surface-mounted integrated circuit. Winding toroids is actually very easy. I don’t know why people make such a big deal of it. Maybe they just haven’t tried. Soldering the SMT circuit, while not that hard, was stressful. That being out of the way, the rest of the kit was a breeze. Being fairly confident of my abilities, I installed the circuit board in the box without trying it first. This way, I could use all the connectors for testing. To my satisfaction, it worked the first time!

My goal with this Rock-Mite is two folds. First, it is a stepping stone to building an Elecraft K1, which I have just started, and second, it provides me with a small emergency radio for my bug-out bag.

I can’t really compare the DC20B to the RockMite as far as performance is concerned, but building the Rock-Mite is easier, and there is no tuning required. The circuit board is slightly smaller. I replaced q6 with a 2sc799. R18=2.2 ohms for a little more power. The keyer is the Pico Keyer from http://www.hamgadgets.com.

I am very exited about building the K1. More on that later…

How big of a radio, and for how much money can you communicate across thousands of miles? What about something that fits inside a box of Altoids mints for $29? The best part is, nobody can ever cut you off!


Rock-Mite PCB

This is the “Rock-Mite” from Small Wonder Labs.
(Google “rock mite” for Altoids-mounted boards!)

Sure, you’ll have to learn morse code… I can’t think of anything that small however that truly can be used as a pocket emergency radio. Add a long wire antenna, a mini tuner, AA batteries, and you are in business. With the “Mity Box,” and connectors, your total cost comes to $70, still a bargain. My RockMite is on it’s way (20m version)!

Another kit I just completed is the DC20B.



You can see that it is a bit more complex than the RockMite. You need to wind transformers by wrapping a certain number of turns across small toroids with very thin wire. The kit also requires tuning. The Rockmite is pre-tuned. Performance is supposed to be better, we will see…

Assembly took a whole afternoon and evening. I had never soldered on a double-sided circuit board, but it turned out to be fairly easy. I just made sure I had a good solder joint on both sides. I started with the smallest components, resistors and diodes, then integrated circuit sockets, capacitors, and transistors, leaving out the final transistor until everything was squared away. To my delight, I heard morse code when I turned it on and attached a long wire! The volume was very faint, hopefully that will change with a tuned dipole up in the air.

There is one little problem remaining. I have also built the frequency counter kit from N3ZI. The oscillator frequency of the DC20B is supposed to be 14,060khz. I get 14,063.2 minimum.

DC20B Frequency off

DC20B Frequency off

Hopefully I will be able to fix the problem. It might be a calibration issue with the frequency counter. Since I do not have an HF Ham radio, I can’t check it. Once I build the RockMite I will have a way to verify the frequency.

[warning]DCxxB builders: C36 has a missing trace to ground. Make sure you solder a short piece of wire from the pad closest to the board edge to the ground..[/warning]

Both the DCxxB and Rock-Mite have keyer chips included. That means it can generate Morse code from an Iambic paddle you plug-in. These radios serve the same purpose. For some, there is the challenge of contacting distant stations on very little power (500mw to 1w). Others take them camping, hiking, and on all kinds of adventures. I am of the second type. The RockMite will have it’s place in my bug-out bag as well. Heck, I might build a second one as a backup.

My choice between the two? Rock-Mite; because it requires no tuning and has no toroids to wind. You can easily find help online, along with a list of possible modifications. Both kits have a Yahoo group. The Rock-Mite group though did not at first accept me! Why? Because I don’t yet have a license and call-sign! The DCxxB group had no problem with me joining. It turns out that the groups are owned by the same person.. And I was accepted at last, after complaining. These kits are a great way to get started, and while groups need to be monitored, access shouldn’t be restricted…

Learning Morse Code turns out to be pretty hard for me. Some people have no trouble and wrap it up in a couple weeks. I’ll be lucky to take only three months! My brain isn’t wired that way I guess.. I use an iPod app: AA9PW Ham Morse. It uses the Koch Method, which is supposed to be better. I had to slow down the learning speed from 15wpm to 12wpm, just to be able to write fast enough. I might just try to build the sentences in my head… I don’t think anyone can write that fast; not me anyway.

As to my HAM license(s), I am in no hurry. I read the Technician class book once and never miss more than one questions on the QRZ.com practice exams. So, I took three General class practice exams, just out of curiosity, passed two! Barely, but still… I am reviewing for that class now. I might as well pass both tests at the same time. Maybe I should get the Extra class as well, why not? If not just to see the face of the examiners, asked which license I am testing for, I’ll say “All of them!” and get close to 100%. Listening to HAM conversations, I have to say that what I have heard isn’t that interesting. It is a somewhat weird crowd. Mostly old fat guys (no offense intended). As to public service, in times of relative safety, radios are useless. You don’t need a ham radio to help with a local fund-raising marathon.. Just use cell phones! I laughed when I heard a “Net,” the controller asking “Is there any emergency traffic?” Are you kidding? We call 911 for emergencies! There is also the “contesters,” who won’t give you the time of day and just want a call-sign and “grid number” to add to their collection. How useless is that? Anyway, there are also great things in Ham radio. Groups do take their transceivers atop mountains and in all kinds of remote areas. I like the idea of it being a safety net, some kind of support apparatus. Besides, you don’t stay in shape by sitting in front of a radio all day…

I will post an article on building the RockMite, with a video, when I get the kit (I was told ten days before it ships).

Here is what comes to my mind when talking about any item: “If it can’t carry you, and you can’t carry it, don’t bother.” These two small transceivers certainly get my thumbs up!

Update (May 27th): I think I am going to ditch the DC20B. I have a box for it, and should complete the build, but after that, it’s going away. I can’t get it on frequency, and I am not the only one… The Rock-Mite kit should arrive this week. I can’t wait to build it. Look for the article!

Update (May 30th): Well, I gave it one last try.. Changed C36 to a 100pF, and C29 to 47pF. It worked! Now I get 14,059.72 on transmit. Receive goes from 14,060.16 to 14,060.32, a perfect 600Hz offset. The problem is the receiver, which has no selectivity. I receive Chinese, French and Spanish commercial radio stations, but little, faint CW signals. Maybe the problem comes from the wire I use as an antenna, which isn’t tuned. I will try a tuned dipole during the day and see if I can get clear CW (morse code). I boxed up the DC20B in a nice Hammond cast aluminum box. I made a hole in the cover to tune CT1 and glued a piece of coax outer insulation so that I can’t touch anything with my screwdriver upon insertion.. The box is a little big, but it looks good and as though it would survive being run over by a semi-truck.. I might make another hole for access to CT2 and add an RCA plug for a frequency counter (for tuning).

Update (August 1st): The tuned antenna did the trick. Good selectivity now, and the radio is on frequency. The DC20B gets the thumbs up!

DC20B Boxed

DC20B Boxed

Note the piece of insulation glued on top of CT1.
I wish that damn iPod could focus up-close.
Still waiting for the Rock-Mite.
I am starting to think about an Elecraft K1.