Purchased in 2005, I finally decided to assemble the kit after 17 years. The assembly took about 5 hours. Before putting the radio in the case, I tested it on the bench. I knew that once it was in the case, it would be very difficult to remove it for troubleshooting or modification. The radio worked the first time I powered it up (I get lucky sometimes). The sensitivity is very good, and the transmitter output was 300 mW. I had tested a pile of 2N2222A transistors before assembly to find the one with the most gain. I’m surprised the output was only 300 mW – not the 500 mW others seemed to be getting. Receive current draw is 23 mA, and transmit is 170 mA. Receive sensitivity measured about 0.5 uV for a readble signal.
I noticed right away that something would have to be done to tame the very loud side tone. The instructions say to to change the value of C8 to lower the sidetone. I tried several values from 0.01uF to 0.1uF but did not find a value that worked as I wanted. I then tried a 0.1uF capacitor in series with a 4.7K resistor. That worked perfectly! Not only did this combination lower the sidetone to a very good level, it cleaned up some of the rough, square wave sound.
Another modification I made was changing the operating frequency of the radio by substituting crystals on a different frequency. The kit came with 10.106 mHz crystals. Even though this is the alternate QRP calling frequency, I have worked 30m CW enough to know that faster CW operators use the lower frequencies in the band. I would have liked to changed to 10.116 mHz, the 30m QRP main calling frequency, but I did not have those crystals in stock. I did find a set of 10.118 mHz crystals. This area of the band usually has some slower CW operators, which is what I needed. I had origionally tested the radio with the 10.106 mHz crystals in place. After the crystal change, the performance was virtually identical.
When I purchased the kit, I also purchased the Mity Box from American Morse https://www.americanmorse.com/mitybox.htm These boxes are machined from billet aluminum. They are custom made for the RockMite. As of the time of this writing, American Morse MFG. still sells the Mity Box.
I plan to put the RockMite on the air soon, and will report on its operations and contacts made.
How did the uBitx version 6 work for you? I have a version 3 that receives well but apparently the audio drive on transmit is too low. I tried replacing resistors in the mic amp but no luck yet.
73 John N4HNO
I have a version 3 (see post on the blog) and a version 6 (also see post on the blog). Both work great on SSB. I have not tried them on CW. I used the stock mic with both. I don’t use them very often these days. I like to build, test to confirm they work, and move on to the next project! 73, Jeff W9TH