Rockmite 40 Meter QRP Transciever

A Small, One Frequency 40 Meter QRP Transciever Project

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.

I have several objectives for this project:

Reliable QRP operation--that is enough power out to be heard and good enough reciever performance to hear under typical band conditions
Ability to interface with simple antennas commonly used for QRP Portable operation, both 50 Ohm and End-fed half-wave wire antennas
Internal batteries that can run for several hours of typical operation, with the ability to run on external power
Solid CW operation using either straight key or Iambic Paddles
Light enough to carry for extended walks/hikes/etc.
Small enough to fit in a camel pack or small rucksack.
Rugged enough to hold up to portable operation transported by foot, by Jeep, by canoe, etc.

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.

I ordered the 40 Meter Rockmite, for 7030, and the "connector and control" kit. These include the circuit board and all the parts mounted on it, plus the required connectors for power, headphones, paddles, and antenna. There is also a pushbutton switch for controlling the PIC processor, a potentiometer for gain control, and a diode to put in series with the power connector to prevent frying anything by hooking it up backwards. The various parts are shown in their plastic bags in the photo above. The US nickel is included to give an idea of scale. This board is pretty small...

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.

The Rockmite board is 2 by 2.5 inches, which is fairly small. It will fit in an Altoids tin or other small enclosure. The most interesting installation I have seen is a complete Rockmite built into a computer mouse, with the left and right buttons used in place of paddles for iambic keying. At first glance the board seems to have places for a lot of parts, but actually there are not so many--it is just a compact design with everything in a small space. The board assembly took me two sessions of about 90 minutes each. If I still had the eyesight of a 20 year-old, it might have taken less time. I use a magnifying glass to augment my bifocals, and have gotten in the habit of double and triple checking component identification and placement.I have built a number of electronic kits, and found this one to be pretty easy and straightforward, with the exception of installing U1, which is a surface mount IC. It is not terribly difficult, but requires some care and very good soldering skills.

It is a bit of a challenge to solder down a chip smaller than Abe Lincoln's head on a penny. (I didn't notice the pocket lint in this photo until I was cropping it for this page--oops!) The surface mount package has four very small leads on each of two sides, and they lay down on very small pads on the circuit board and have to be soldered in place. I don't know why the surface mount package was used--the same chip is available in DIP packages just like the other two chips used in this kit. Then you would simply need to solder in three chip sockets, and not have the additional worry of a surface mount component. All the other parts mount conventionally, and it is not too onerous to install U1, but. it would be a more suitable kit for less experienced builders without the surface mount. It is not dificult for someone with decent soldering skills and good eyesight, but overall I would not recommend this as a first kit.

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.

There is no extra room on the board, so good technique and a bit of planning at each step helps a lot. Once you get things going, they seem to go quickly. A normal soldering pencil and basic hand tools are all you need. I have a 15 watt soldering pencil from Radio Shack that worked just fine. Too much heat and you might damage the board, so good technique and small wattage pencil are iimportant. The photo above shows the board at the end of my first 90 minute soldering session. I worked at a fairly leisurely pace--it is much more important to get the parts in the right place, with the right polarity, and with a good solder joint than it is to get them in fast.

After a second session the next night I had the board completely populated.

It took a bit of coordination to make sure the crystals were elevated from the board as recommended and their cases grounded. I have never seen a ground applied to a crystal like this, and can see that it may complicate using socketed crystals to change frequency if it is actually needed.

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...

With power applied and hooked to a 40 meter inverted-V I was able to hear CW! The reversing function seemed to work also. With a dummy load I was able to hear sidetone, and transmit to my IC-718. I haven't hooked up a power meter sensitive enough to measure 500 mW reliably. I will likely have to use a 'scope and make voltage measurement to see how much power out. Since the testing seems to show normal operation, I just have to intall the board in a case, with suitable batteries and tuner, and I should be ready for portable operation.

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 plan to mount the Rockmite board on the side, a bit more centered than it is in this photo. The controls and LEDs would be on the top, which is facing away from the camera. Antenna connection will be on the right end and power, phones, and paddles on the left end, as seen here. This opening would still be in the bottom, with the plastic lid acting as a non-skid base. the mounting location of the battery holders will be worked out after I finalized the power filter and regulator.

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!

Useful and Interesting webs sites, with Rockmite information:

Small Wonder Labs who make and sell the Rockmite and other kits.
The Hampton County Radio Association Rockmite page has great information and links to even more great information.
The Rockmite Files is a great collection of installation examples and operating information.
Better QRP Kits is run by Stu, KI6J; makes and sells the EFHW Tuner kit. Great looking little QRP tuner for End-Fed Half-Wave antennas on 40 through 15 meters.

If you have comments, suggestions, or know of really good Rockmite information sites, please e-mail me! !