On 2/14/2020 1:04 PM, Jim Brown wrote:
On 2/14/2020 11:40 AM, Fred Moeves wrote:
Can you figure out impedance of coax with a device like the Rig Expert?
Yes, if it's a model that can be calibrated, and if the calibration is
properly done, and if it's a model that can export measurements to a
computer. Calibration requires of Standard Short, Open, and Load parts.
Once you've calibrated, sweep a length of the coax with the far end open
and again with it shorted. Export the data to a computer, then import it
into AC6LA's free ZPlots Excel spreadsheet and follow his instructions.
For the measurements, the coax must be connected at precisely the same
point as where the calibration was done.
Before attempting this, study parts of the manual for the equipment that
talks about the "measurement plane."
73, Jim K9YC
This is the "hard" way to measure Zo. Been there, done that.
The easy way is to attach a small 100 ohm (non-wire-wound) pot to one
end of the coax and attach the other end of the coax to any old
impedance meter. Even an MFJ-259 will work. Now adjust the pot until
you see a constant impedance across all frequencies. Don't worry about
what the impedance meter says this impedance is. Instead, measure the
DC resistance of the pot. More accurate. Foolproof.
Rick N6RK
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