I have page on my website with details and circuits of various noise cancellation circuits including the SEM.http://g8jnj.webs.com/rfnoisecancellation.htm
Don't expect too much from the design. It can work under some circumstances. But most of the time you may find that it does very little.
Most of the perceived noise cancellation is actually just a psycho-acoustic effect, associated with reducing the signal level. This is very apparent when using it in conjunction with an SDR radio with real time spectrum display. In many cases, both the signal and noise level are reduced to the same extent. The actual signal to noise ratio remains more or less the same.
But using the SEM I can obtain a 30dB notch on a spurious signal from my home alarm system control panel. But this takes a lot of fiddling with the controls, and does not remain stable over a long period of time.
Martin - G8JNJwww.g8jnj.webs.com