I'm looking to build to a phase shifter circuit that can supply about 60
degrees of phase shift at 70 MHz (bandwidth not important). The phase shift
needs to be adjustable in real time, ie, with a variable R or C.

The catch is that the input and output of the network needs to remain
matched to 50 ohms.

Can this even be done with purely passive components?

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

Thanks very kindly

"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.