On Mon, Nov 2, 2020 at 08:06 AM, schweppe wrote:
Disconnect your antenna and leave the koax open. Then measure the
reflexion factor in dB at the other side of the koax. The loss in koax
is now half the reading of the reflexion factor at each frequency.
You do get 'ringing' (reflections) right across the frequency range when you measure coax loss using just the S11 reading. So you will get a large variation depending on whether the far end of the coax is open or short. You can use either a short or an open(either is fine) so long as you take into account this 'ringing'.
This graph will shows this 'ringing' and so shows what it looks like and shows the two different S11 readings, one for open coax and one for short coax. At the low frequency end (left) their basically 180 deg out of phase, but then change to almost in-phase at the high frequency end (right). I added a coax loss graph (top right) that removes the 'ringing' and shows a readable coax loss from both a far end open or short (same result from either/both), it also shows the short/open end impedance on the bottom right graph and the coax length on the bottom left graph ..
