It's Wed, 10-22-14.  I don't know if my computer calendar has adjusted. Good Morning to All.

Our last topic was radios in the 30's and 40's. The first radios were using earphones, then speakers. The dominant design then was the direct conversion receiver, the signal was rectified then fed to an amplifier. Then Armstrong discovered a way to improve reception and his designed became popular for quite sometime. he introduced the Reflex radio circuit wherein the signal is fed back into an earlier stage as to cause an oscillation at a frequency. There a knob to adjust the feedback to a ax point. Reception dramatically improved when someone not only amplified the RF signal before detection but but also greatly improved selectivity, keeping s station tuned and rejection neighboring channels. This technique was mixing the incoming frequency with a locally produced signal. Then the differential signal was sent to s series of tuned amplifiers, before detection. The result was amazing. No more fussing  of the feedback knob. This design was called the superheterodyne system. Superhet for short.