phase shifter circuit needed

"Patrick" bravely wrote to "All" (03 Jul 05 22:32:10) --- on the heady topic of "phase shifter circuit needed"

Pa> From: "Patrick" Pa> Xref: aeinews sci.electronics.repair:52356

Pa> I'm looking to build to a phase shifter circuit that can supply about Pa> 60 degrees of phase shift at 70 MHz (bandwidth not important). The Pa> phase shift needs to be adjustable in real time, ie, with a variable R Pa> or C. Pa> The catch is that the input and output of the network needs to remain Pa> matched to 50 ohms.

Pa> Can this even be done with purely passive components?

Pa> (Specifically, what I have is a transmission line that needs to Pa> provide a 180-degree shift from the start of the line to the end. The Pa> problem is we have no way to precisely measure the length of the TL. Pa> So we need a way to adjust the "length" of the line in real time. Now, Pa> I'm aware of the trombone method, wherein a piece of TL is slid in and Pa> out to provide a variable lenght. However, this is a mechanical Pa> solution and not suited for the application; ergo I need a way simulate Pa> this behaviour) Pa> Thanks very kindly

Try looking into active all-pass filter networks. This requires a few transistors though.

A*s*i*m*o*v

... Transistor: The sister that used to be your brother.