Richard, G3CWI, wrote:

What would be the best way to adjust a quarter wave
of 75 Ohm twin line using an antenna analyser? I just
connected mine across the analyser (open circuit) and
looked for the freq where a short showed - is that
likely to be accurate? At 10.1 MHZ I ended up with a
15.7 foot line which seems a bit short (low velocity
factor).

With an open-circuited stub, there is always a bit of
fringing capacitance around the open end which will
throw the measurement off a bit. A short-circuit
measurement is generally more accurate.

Jim, K7JEB