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