To fill some of my Winter hobby time, I decided to build a very portable QRP rig. I like to build some of my own equipent, and prefer to use kits when they are available. I have recently had my interest in CW rekindled, and enjoy being able to operate portable, usually in combination with other hobbies.
The Rockmite, from Small Wonder Labs, has been around a while, and combines a fairly simple and easy to build design with some very useful operating features. It is crystal controlled for one frequency, which is both a limitation and a design asset. You are limited to the one frequency, but by optimizing for that one frequency you get some very good receiver performance. There are simple ways to modify the kit to allow the crystals to be changed, and I may look into modifying later to do so. Initially, after consulting with a friend who may also be building one, I settled on a kit with 7030 KiloHertz crystals, which is the 40 Meter QRP calling frequency.
The rockmite kit is just for the circuit board, with an accesory kit available with connectors, switches, and such. Mounting and enclosure are up to the builder. The basic Rockmite board will fit easily into an Altoids tin, but I wanted to include everything in one package. Of course, the next setp is to decide exactly what "everything" includes. At minimum for my project, that will be the transciever board, suitable batteries, and an antenna tuner to allow use of end-fed half-wave antennas. I plan to build the whole thing into a flavored instant coffee tin. I will update with more on the final installation as it progresses, but wanted to start this by detailing my experiences with construction of the Rockmite board.
Small Wonder Labs is run by Dave Benson, K1SWL. He has several interesting kits and products for hams, and I look forward to trying out some more of them in the future. Several things drew me to the Rockmite, including a simple design, the time it has been on the market and the number sold, and the large online community of users, which has a large data base of constructin and operating tips, mods, etc. I subscribe to the Rockmite group on yahoo, and have researched a number of sites with information and examples. I will add a list of relevent links at the end of this page.
One major advantages of building a Rockmite kit is the very affordable price. My kit was just $29 dollars, plus $16 for the optional "connector and control" accesory kit. I have a hard time opening Icom HF rig and playing around with the design, partly because of the caost and partly because of level of manufacturing detail. It just isn't meant to be tinker-friendly. On the other hand, a radio that I assembled myself, and that i understand thoroughly, can provide a lot of opportunity for applying mods, redesigning, and generally tinkering around with its circuitry. The worst case, if I seriously goober it up beyond repair, is to order a new $29 dollar kit and start over.
In spite of the small size, this little transciever has some pretty impressive features. An 8-pin PIC processor is used to control the T/R offset and provide an iambic keyer that will work with paddles, or a straight key. The reversable T/R offset is 700 hz, and provides a built-in sidetone, as a bit of the transmitted frequency is coupled back to the receiver. A crystal is used to provide the basic frequency for the oscillator, with a second crystal on the same frequency used to narrow the receiver front end. The single board provides a 500mW transmitter, a direct convertion reciever, and automatic full-QSK T/R switching.
As recommended, I started by soldering on U1. Next I put on the two IC sockets and moved on to installing all the capacitors and three inductors. By installing a few
components at a time, scattered around the board, it wasn't hard to make quick progress. I avoided putting in parts that were bunched up, rather putting in a few at a time
that were spaced out a bit. This kept the leads far enough apart to solder and trim them easily.
After a second session the next night I had the board completely populated.
Another area that requires some care is installing the PA transistor, Q6. You need to attach the heat sink before installation and then ensure as it is placed on the board that the heat sink doesn't contact any resistor leads. I added 10mm insulated standoffs to help with airflow around board and they came with screws and washers to mount them to the board and case.
I soldered in wires for the various connections to allow testing. Note the capacitor with the lead extending to the right, which is the antenna connection. This
capacitor and an inductor were supplied on a suplimental sheet. they form a series resonant circuit to reduce spurious emissions, and you should ensure you install them.
With the test leads soldered on it looked like the kit was having a bad hair day...
The enclosure I am going to use is a coffee tin about 2.5 by 2.5 by 4 inches. This should be plenty of room to include a small tuner, batteries, and voltage
regulator and filter.
I currently plan to be able to use external power, switch between external and battery power, and have a power-on indicator LED.
I also plan to use end-fed wire antennas. This means the associated switches, tuner, and a tuning bridge will need to be compatible and compact to work with the Rockmite. I have ordered an EFHW Tuner from Better QRP Kits but haven't built it yet. Details will be included as they are worked out. Please check back from time to time to see if I am making progress. Of course, once the rig is built I will need to start looking at QRP antennas!
If you have comments, suggestions, or know of really good Rockmite information sites, please e-mail me! !