# phase shifter circuit needed

Discussion in 'Electronic Repair' started by Patrick, Jul 4, 2005.

1. ### PatrickGuest

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

2. ### AsimovGuest

"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.