A business card size homebrew 40 meter XCVR project from Ray Ring: I tweaked my previous XCVR design to use push button tuning and made the board layout extremely compact. I improved the side tone injection to be absolutely  perfect – not too loud, full break in and no clicks. I went…
Source: 40 meter XCVR size of an business card with 1 watt output, 7.000 to 7.150 MHz coverage