This service manual includes the the device circuit diagrams.
http://www.rane.com/pdf/old/mp24sch.pdf
lots of projects published in the UK magazine Radio Control Models and Electronics
http://www.welwyn.demon.co.uk/
a magneto-resistive sensor to detect small magnet displacements without resorting to a precision voltage reference
http://www.edn.com/archives/1994/080494/16di1.htm
http://ourworld.compuserve.com/homepages/Bill_Bowden/page9.htm#twin_t.gif
http://website.lineone.net/~dezellis/rc5.htm
Download free project plans for radio direction finders and locators.
http://home.earthlink.net/~w9xl
measures your reaction time, and can be built on a breadboard.
http://www.nutchip.com/progetti/react_en.htm
Down-converter to 5V for receiver use.
http://www.uoguelph.ca/~antoon/gadgets/reg-rx.htm
Sensitivity of multi turn receiving loops.
http://www.lwca.org/library/articles/ywk/looptheo.htm
http://www.mrs.bt.co.uk/dubus/8604-5.pdf