The microR2 is currently out of stock. The plan is to redesign the rx using surface mount technology. I can not guess how long this will take - everything takes so much longer since I had my stroke.
The microR2 is KK7B’s latest receiver design. Similar to the miniR2, it is a DC receiver that uses phasing techniques to provide opposite sideband rejection. But…the microR2 is a complete receiver including a tuned LNA and VFO on a single small circuit board. The VFO uses a reduction drive variable capacitor mounted off the circuit board. There are five transistors, five op-amps, four toroids and four adjustments: LNA tuning; VFO band-set; phase trim and amplitude trim. All adjustments may be made while listening to a CW test signal. Some design trade-offs have been made for simplicity and ease of adjustment. The opposite sideband suppression is not quite as good as the miniR2. The microR2 uses a fourth-order audio phase shift network, and is designed to have selectivity very similar to the classic 4 pole filters in receivers such as the Drake 2B and R4B--good enough to reject all but the strongest signals. The LNA has a sharp single-tuned circuit in the output stage. This helps reject shortwave broadcast interference and makes it very easy to adjust—but limits the range to about 100 kHz at 7 MHz without retweaking the LNA tuning. The audio stages include a number of low-pass sections both before and after the audio gain, but the low frequency response has been extended to much lower than in the miniR2 or R2Pro. This makes the microR2 more susceptible to hum pickup from nearby ac transformers—not a problem with batteries or an external AC power supply. There are no compromises in audio quality, and the increased low frequency audio bandwidth means the microR2 sounds even better than previous KK7B receivers.
The microR2 is currently available for 40 meters only. The board size is the same as the miniR2. The kit includes a reduction drive variable capacitor, the PC board, and all electronic components. All you need to supply are the connectors, knobs, hardware, some hookup wire, +12 volts, and an enclosure. It makes a very nice mating receiver for the Universal QRP transmitter MKII, or a tunable IF for the higher frequency bands. Documentation for this new receiver is minimal – a schematic, a parts layout, some construction notes I have written, and a parts list. An article on the microR2 is in the October 2006 issue of QST. A copy of the article is included with the kit.