Sunday, July 29, 2007
Phasing Receiver Block Diagram
The phasing version receiver is a little more complex, and introduces phase shifting circuitry. Since we will be using one of the 500kHz resonators for L.O. frequency control it is not possible to run the L.O. at 4X the desired injection frequency and then use a pair of divide-by-2 Flip-Flops to generate the quadrature phase. While not a show-stopper issue, this does introduce some interesting problems. 500 kHz is way too low a frequency to allow use of tuned coaxial stubs to get a 90 degree phase shift. But, since this is a fixed-frequency receiver we can probably use LC networks for the phasers. EMRFD, Page 9.14, shows how this might be accomplished by using over-coupled LC transformers. This provides a rather simple method for deriving the needed phase shift at the L.O. operating frequency.