On Nov 3, 9:16*am, Jeff wrote:
On 03/11/2010 15:46, KD7HB wrote:





On Nov 2, 11:22 pm,
wrote:
Hi all,

For my project, I want to perform Distance to fault measurement in the
cable connecting the antenna. The principle is that a signal should be
sent to the cable and using the forward and reflected voltage VSWR
should be calculated and should be viewed in a spectrum analyzer. My
question is

1. *What transducer is used to detect the transmitted/reflected signals
from the cable?

2. Should the transducer be connected in series or parallel?

Anyone, Please help

--
ashwanthh

No transducer. Use an oscilloscope to measure the time between the
emitted pulse and the reflection of the same.

KD7HB

just to add to that Google Time domain Reflectometer.

Jeff

Yup, that's the default instrument, but a fast-rise-time pulse
generator and a wideband scope will do it, too. I created a TDR
accidentally when I thought I was just measuring rise times on the
input and output of an amplifier. (I had inserted a T-connector,
creating an impedance mismatch, which showed up as a reflection. When
I saw the glitch on the trace, I puzzled over it for about half a
minute before it dawned on me what I was seeing.)

However, if this guy feeds his spectrum analyzer with a tracking
generator and tee's off to the unknown cable, the reflected energy
from the cable fault will generate a comb of nulls. The frequency of
the first (lowest frequency) null will indicate either the quarter-
wave point or the half-wave point (depending on whether the fault is a
short or an open. You'd need to know the velocity factor, too. I
don't see how VSWR would come into play.

Yeah, I'd really rather have a TDR, hi-hi.

By the way, this arrangement also works to approximate the resonant
frequency of an antenna. The comb of nulls will flatten out -- be
less pronounced -- at the resonant frequency, due to the incident
energy being radiated, rather than reflected.

"Sal"
(KD6VKW)