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

On Nov 2, 11:22*pm, ashwanthh
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

On Nov 2, 11:22*pm, ashwanthh
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

Forward and reverse power are normally resolved using a "directional
coupler." Such a coupler can also be thought of as a bridge circuit.
Directional couplers can be built in various ways. For example, the
free-ware RFSim99 program, under tools--component--coupler shows
five different ways to build a directional coupler. That program
doesn't show the Wheatstone bridge form of directional coupler, but
those are also common, especially where a wide range of frequencies is
to be covered. Wheatstone bridges are generally used with equal (e.g.
50 ohm) arms in test and measurement equipment that runs low RF power
(because such a bridge must dissipate most of the RF power fed to it),
and with very unequal arms when high power is to be handled (resulting
in a low coupling factor; -40dB is common). Please note that
directional couplers must be designed for the impedance line they are
used with (and ideally, the calibration should be verified).

In your project to locate faults, you may wish to consider not only
the ratio of forward and reverse power (e.g., SWR), but also the phase
relationship between the two. The rate of change of phase as
frequency is changed should tell you how far away a single fault is;
multiple faults are more complicated.

Cheers,
Tom

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

On Nov 3, 6:22*am, ashwanthh
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

look up time domain reflectometers... they are much simpler than what
you are thinking of. using a simple step input wave you measure the
time to the reflection. if you get fancy you can measure the polarity
and size of the reflection to determine if it is a short or open or
impedance change... if you really get fancy you can hook a scope up
and look at more details. the only transducer needed is a voltage
probe OR a current shunt, either one will work depending on the
installation needs.

K1TTT wrote:
On Nov 3, 6:22 am, ashwanthh
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

look up time domain reflectometers... they are much simpler than what
you are thinking of. using a simple step input wave you measure the
time to the reflection. if you get fancy you can measure the polarity
and size of the reflection to determine if it is a short or open or
impedance change... if you really get fancy you can hook a scope up
and look at more details. the only transducer needed is a voltage
probe OR a current shunt, either one will work depending on the
installation needs.



Or, use the technique used in vector network analyzers..

Sweep the frequency, do the fourier transform to find time domain.

If you're using just power detection, it's more like getting the
autocorrelation or power spectrum of the reflected signal vs frequency.

K1TTT wrote:

On Nov 3, 6:22 am, ashwanthh
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

look up time domain reflectometers... they are much simpler than what
you are thinking of. using a simple step input wave you measure the
time to the reflection. if you get fancy you can measure the polarity
and size of the reflection to determine if it is a short or open or
impedance change... if you really get fancy you can hook a scope up
and look at more details. the only transducer needed is a voltage
probe OR a current shunt, either one will work depending on the
installation needs.

If the school project requires him to use a Spectrum Analyzer, then the time
domain may not be an option.

On Nov 3, 10:31*pm, joe wrote:
K1TTT wrote:
On Nov 3, 6:22 am, ashwanthh
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

look up time domain reflectometers... they are much simpler than what
you are thinking of. *using a simple step input wave you measure the
time to the reflection. *if you get fancy you can measure the polarity
and size of the reflection to determine if it is a short or open or
impedance change... if you really get fancy you can hook a scope up
and look at more details. *the only transducer needed is a voltage
probe OR a current shunt, either one will work depending on the
installation needs.

If the school project requires him to use a Spectrum Analyzer, then the time
domain may not be an option.

if the school project is requiring a spectrum analyzer to measure
distance to a fault location then its a pretty dumb project. there
are much better and more straight forward ways to do that.

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)

K1TTT wrote:


if the school project is requiring a spectrum analyzer to measure
distance to a fault location then its a pretty dumb project. there
are much better and more straight forward ways to do that.

Not if the purpose of the school project is education, and understanding
the relationship between frequency domain and time domain.