Although this calculator was designed for coaxial feedlines, it also works for balanced line length from antenna to transmatch, or from antenna to short coax jumper connnected to a transmatch. You simply process the calculator results as follows:
(Resulting coax length in feet x 450 ohms)/450 ohms = ladder line length in feet
The final figure will give you a balanced line length that should easily be handled by a good external transmatch.
Be sure that you scroll to the bottom of the page after using the calculator; there you will find an easy-to-understand explanation of the concept.
Built-in antenna tuners are generally less tolerant of a mismatch, so you'd want a feedline length in multiples of a half-wave (current maximum points). That would be approximately 32', 64', 96', etc, although some slight adjustment might be required to compensate for variations in velocity factor.
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