I missed what was actually being tested....
Also, if one is testing cables themselves, is there a finite distant limit?
BR
Tim K4SHF
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On Mon, Jan 6, 2020 at 6:28 AM Dana Whitlow <k8yumdoober@...> wrote:
Robert,
It would be desirable if you could also measure the transmission through
the
cable, including both magnitude and phase versus frequency. Plus any info
you have about the supposed characteristic impedance and velocity factor of
the cable. Extend the lower frequency limit down to 50 kHz as well.
A second set of equivalent plots but with the nano's scan set for a span
of about
10 MHz and a center frequency well up in the VHF regime (~150 MHz would be
fine) might also be pretty informative. These should also include the
scan of the
termination that you're using by itself.
The overall shape of the plot is somewhat consistent with two point
reflections
of roughly equal magnitude, separated in round-trip time by a bit under
500 nsec.
However, the deteriorating overall return loss at increasing frequency is
not really
consistent with that simple model. But if your connections to the hard
line were
a bit crude, creating added impedance bumps at the two ends, the curve
I've seen
so far would be better-explained.
Could you also send a photo showing exactly how you are physically
interfacing
to the hard line from the small cable environment?
What I've seen so far suggests a cable whose impedance is not really 50
ohms,
combined with some other issue such as (perhaps) impedance bumps at the two
ends. The period of ~2 MHz seen in the S11 plot is not consistent with
a physical
length of 350 ft- in fact it's off by almost a factor of 2 if one assumes
a VF of 0.67.
Dana K8YUM
Tim K4SHF