On 6/9/23 12:01 PM, Roger Need via groups.io wrote:
On Fri, Jun 9, 2023 at 09:21 AM, Anne Ranch wrote:
I shall repeat
the task is -
is the unknown length of cable in multiples of 1/4 wavelength @ 14 MHz band,?
hence
what should the sweep frequencies be ?
Why are you using TDR to do this task? Just sweep from 50 kHz to 20 MHz and set yellow trace to s11 Phase and Green to Smith chart. Then just spin the marker and you can see what you want. Attached is a plot of a 9.4 meter long piece of RG58. The markers show the 1/4, 1/2, and 3/4 wavelength frequencies. At 14.16 MHz. this cable is about 0.5 +.25(144/180) = 0.7 wavelengths long
It's useful to know how to make the TDR work - I've found more than one feedline problem by using TDR - yeah, sometimes if there's combinations of solid, foam, and air dielectric, the distances don't work out, but you can still see the discontinuities from connectors.
Attached is a TDR plot with a feedline to an S-band antenna with multiple segments, and the actual antenna at the end.
