Hello all,
to give some ideas about the TCL values of a practical segment using screw terminals and shielded AWG18 cables, I just calculated the TCL values from the MMVNA-100 raw data of the measurements shown in the presentation https://www.ieee802.org/3/dg/public/May_2022/graber_3dg_01_03152023.pdf.
The green limit curve is one of the suggested limit lines for TCL during the last meeting (TCL [dB] = 50 – 20 * log10(f / 10), with f in MHz from 0.1 to 60 MHz), an alternative suggestion was to use a curve 10 dB above (TCL [dB] = 40 – 20 * log10(f / 10) ), with f in MHz from 0.1 to 60 MHz).
Looking into the measurement data both suggested limit lines would be exceeded. Partly the connectors, but also the use of a shielded cable (which often has a worse TCL values than a comparable unshielded cable, as it relies also on the shield for noise attenuation) are likely relevant for exceeding the suggested limits.
Based on the given measurements described in above mentioned presentation, a possible TCL limit could be described by the blue curve below (TCL [dB] = 30 between 0.1 and 5 MHz and TCL [dB] = 27 – 10 * log(f / 10) between 5 MHz and 60 MHz, f in MHz), or something similar.
Also the question would be if we want to have a TCL limit not only for unshielded segments (as for 10BASE-T1L), but also for shielded segments.
Regards,
Steffen
Segment A is the segment between VNA Ports A (near end) and C (far end), while Segment B is the segment between VNA Ports B (near end) and D (far end) in above mentioned presentation.
