What doesn't seem to agree between theory and practice is that
measuring any "b" stub in parallel with the dummy load shows an
impedance of about R=11 and X=11, while on the smith chart this should
be R=11 and X=21 (obviously all at 70 MHz). Why it does measure right
alone and wrong with a coaxial "T" adapter and the dummy load in
parallel?
Of course in real life I'm assuming a Vf=0.88 for the cellflex cable
and checking measures with the analyzer.

What could be wrong?
Any hint is appreciated

73 de Frank IZ8DWF

In simulation I am getting 86.8 degrees for the shunt stubs, and
62.4 degrees for the series coax between stubs. Seems about
the best compromise with results as follows:

65 to 75 MHz S11 -10 db
65 to 75 MHz S21 -1 db
88 to 90 MHz S21 -16 db
90 to 116 MHz S21 -20 db.

73, Also Frank (VE6CB)