Forgive me for asking questions about seemingly obvious things, but
something isn't as it appears. If it's really like you've described, the
phase difference should be 90 degrees.

Please verify that the added 50 ohm quarter wave section is between the
end of the 75 ohm line and the 50 ohm terminator/probe connector as you
described and not between the signal generator tee and one of the 75 ohm
lines. If the latter, you will get something other than 90 degrees of
phase shift, although I haven't run the numbers to see what it would be.

Are you sure the added quarter wave line is 50 and not 75 ohms?

Also, what's the ratio of voltage magnitudes at the two probes?

Roy Lewallen, W7EL

Gary Schafer wrote:
I am using an HP 8405A vector voltmeter to try and measure the delay
in a transmission line in the 2 meter band.
This is part of a phasing harness for a pair of 2 meter antennas to
put them into circular polarization.

The set up is as follows: A T connector on the signal generator with a
pair of 75 ohm ¼ wave length jumpers from either side of the T. At the
ends I put an adaptor and a bnc T connector of which one side connects
to the probe of the 8405A and the other end of the bnc T is a 50 ohm
load.
The other 75 ohm ¼ wave jumper has the same setup with the bnc T, 50
ohm load and B channel probe of the 8405A.

With this I see a zero degree phase difference on the 8405A as it
should be.
Then I insert a ¼ wave length 50 ohm cable between one of the 75 ohm
cable ends and the bnc T connector / 8405A probe connection point.
There are the same number of adaptors in each side of the lines. The
only addition is one barrel connector and the ¼ wave length of 50 ohm
cable. (this is in the B channel by the way)
The additional barrel connector is part of the ¼ wave length on the 50
ohm line.

The wanted frequency is 145 Mhz.
Rather than seeing 90 degrees delay with the added 50 ohm line section
I only see 60 degrees of delay?? If I run the frequency up to around
180 Mhz I get the 90 degrees delay shown on the 8405A.
What do you suppose I am doing wrong in the measurement setup?

I have measured the delay on the 50 ohm line section by itself (with
the one barrel connector) and I see 90 degrees of delay at 145 Mhz. I
used 20 db pads on each side of the T from the signal generator to
isolate the two sides of the test setup when measuring this cable by
itself.

Thanks
Gary K4FMX