John,
Good stuff!
Thanks for the write-up.
# Higher frequency applied signals get bigger changes in phase for a given distance
# to a reflecting fault and thereby allow better resolution. Wide frequency spacing
# of signals shortens the maximum unambiguous measurement range. Signals spaced,
# say, every 30MHz (3000MHz/100 steps) cannot distinguish reflections at 33.3ns and 66.6ns.
...
# "Adjust ELECTRICAL DELAY to move the displayed window to the desired location along the cable"
# This extends the good resolution to greater lengths, still subject to the ( 1 / (frequency-step-size)) limitation
So if we do at 3000mhz/100=30mhz steps, then window into the region around 66.6ns,
I believe you are saying that our reading will be confused by stuff that happens at 33.3ns.
Likewise, if we are looking at 33.3ns but our cable is greater than 66.6ns long, we could get
confused by stuff that is happening at 66.6ns. Correct?
John seems to be saying that tmax (the maxi delay through the coax in seconds) is 1/fstep,
where fstep is the step size in Hz. With 100 steps, that is the fmax (the max frequency)
divided by 100. tmax=1/(fmax/100)=100/fmax.
With 100 steps and a minimum frequency of close to zero, the step size is fmax/100,
and tmax=1/(fmax/100) = 100/fmax
In post 17561, Neil said that he found the relationship between max frequency and
the max delay through the coax was tmax=39/fmax.
Curious that there is a greater than 2:1 discrepancy.
I may have to play with it and see.
Jerry, KE7ER
