SOTA will have read about this on the SOTA Reflector, but during the last couple of months Richard G3CWI has been activating summits using a 30m transceiver powered by a 9V PP3/MN1604 battery. This apparently is in response to a challenge set by another keen SOTA activator: Kjell, LA1KHA (who visited us in October 2009.)
I couldn't find many details of the challenge, so I'm just assuming that it was simply to see how many activations could be made using a radio powered by one of these small batteries. Kjell is believed to be using a Small Wonder labs RockMite but Richard built his own transceiver especially for the challenge. The receiver uses a two-crystal ladder filter at the signal frequency, an NE602 mixer, a low noise AF amplifier and active lowpass filter using CMOS op-amps. The transmitter has a crystal oscillator, bipolar buffer, bipolar amplifier and FET class E PA giving 300mW output and an internal Tick1 keyer.
With this transceiver Richard has now activated 10 summits making more than 100 contacts, still using the original PP3 battery! Having established that a PP3-powered transceiver is adequate for reliable activating Richard is now looking for ultra-lightweight HF antennas to get the weight of his portable station down to the absolute minimum.
I think this is a fascinating challenge and hope that Richard will write up the experience in more detail one day, perhaps in his RadCom Portable column or in the G-QRP Club magazine Sprat. This is really what QRP is all about, reducing the equipment to the bare essentials. It also shows the value of CW as the only mode that allows you to use such simple equipment.