Ok, I don’t know how valuable this “emergency” transmitter will actually be but, you could just throw it in your backpack or drawer. Also makes for a nice code practice oscillator. Transmitter is housed in a whiteboard marker case. Green lead clips to antenna (or wire fence) and other leads to battery (<12 volts). I am using a 7.159 mhz crystal and N2222 transistor. I have mine in my junkbox and pull it out when I want to play with a simple transmitter – without an external antenna it will only transmit across the room. And it is just a fun little build. Outside you could hook it to a barb-wire fence, found piece of wire, windmill tower. The originator (K7NS) got about ten miles line of site reception. Of course, no filtering but then in an emergency situation that is a plus.
This schematic is from here: Easy Ten from K7NS
Or you could always just put the parts in a plastic bag with the schematic and keep it in your backpack, never know when it might come in handy.
I haven’t measured output yet but did build a little holder with a Arduino controlled servo to push the button key while I wander around outside to check reception. Will update this blog when I get my rf power meter built (again). Need some IN60P diodes.