Jerry Martes wrote:
"I`m considering building a slotted line for measuring impedance at 137
MHz."

The 2nd edition of the RSGB "VHF-UHF Manual" has a home-built "trough
line" on page 10.26. Dimensions are given for 50 ohms and the line is
expected to be usable down to 145 MHz at its length of 36 to 40 inches.
It needs to be at least 1/2-wavelength.

Best regards, Richard Harrison, KB5WZI