# Variable-step mode rejects a transmission line

Use the documented analysis/integration combination and check whether the selected line model supports variable stepping.

## Compatibility

2.9.0 release target; review-build/source evidence

Published guidance with release-applicability limits. Confirm package applicability before following this guide.

## Check the exact restriction

The maintained manual documents variable-step support for PHASE analysis with BDF integration. LOSSLESS transmission lines block this mode; an untyped T element defaults to LOSSLESS.

## Choose a valid run

1. Read the diagnostic's list of blocking lines and check the model assigned to each.
2. Use a validated fixed-step setup for LOSSLESS lines.
3. Use LCLADDER only when its finite LC-ladder approximation is physically appropriate. Do not change the model merely to silence the restriction.
4. Repeat the calculation with a smaller nominal step when validating edges or amplitudes; accepted settings alone do not establish convergence.

## Sources and verification details

Recorded inputs/builds only. Complete walkthrough and final-package acceptance remain separate.



- support:SUP-016: Generalised editorial finding; outcome qualification retained
- josim-pro:docs/manual_source/sections/troubleshooting.tex: Variable-step mode or runtime options are incompatible with the netlist
- owner:technical-review-20261102: JoSIM-Pro 2.9 chosen as the public starting path; release availability must be checked before publication

- Support history informed this draft. Current-source guidance has been checked; a fresh walkthrough on the intended distributed release and product-owner review remain pending.

## Related guides

- [Choose a transmission-line model before importing external network data](/knowledge-base/josim-transmission-models)
- [JoSIM®-Pro reports that the matrix has no solution](/knowledge-base/josim-singular-circuit)