"Richard Harrison" wrote
Cecil, W5DXP wrote:
"---a two foot long section of 50 ohm coax is all the length needed to
force the V/I ratio to be 50 ohms at HF---"

At 3 MHz?

When power is applied to a transmission line, energy from the power
source doesn`t appear everywhere along the line at once.
( much clippage)
Just how short can a transmission line be and still enforce its Zo? A
1/4-wave matching section inverts impedance between its ends by
enforcing its Zo.
For Zo to equal the square root of L/C, (a resistance), XL must be much
greater than R, and XC must be much greater than G. These restrictions
impose frequency limits on Zo. And, these restrictions may place a low
frequency limit on how short a line can be and still enforce Zo.
______________

For a concept of what that length actually is in the real world, recall that
Bird Corp and others supply directional wattmeters giving reasonably
accurate measurement of forward and reflected power -- leading to an SWR
value. The coax sampling sections for RF frequencies at least as low as 540
kHz. is around 9" in length.

RF