Press space to start!. Presents… Page 0100 0100 Text-TV Your favourite Channel Monday 18. October...

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Presents…

0100 Text-TV Your favourite Channel Monday 18. October 1999

Connecting and

Return Path

in CATV Networks


You have probably seen this before...


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Your favourite TV Channel

News.............. 110

Sport ............. 200

Latest ............ 130

Advertising .... 700

TV today ........ 320

Cabelcon …..... 600

Right? - and you know why too!

0605 Text-TV Cabelcon Connectors Monday 18. October 1999

Lacking system performance…!


Safe signs of poor system performance with analogue TV

signals:

Ghost picturesGhost

pictures


Like this...


Safe signs of poor system performance with digital

downstream signals...

Increased bit error rate.

Typical “visible” results of this will be...


• TV-Text unreadable.

• Noisy (or no) digital sound (NICAM).


- and at digital upstream signals?(using the return path band)


Poor system performance in a CATV network could originate

from…• Poor return loss values

• Poor carrier to noise level

• Insufficient screening followed by...

• Ingress of noise and unwanted signals


There can be many reasons for decreased performance.

Here we will concentrate on...

• Poor or incorrect cable preparation and connector installation.

• Unreliable connector quality.


Most return path problems originate at the subscriber’s end of the

network...

• It’s a well-known fact, that 75-80 percent of service calls are related to drop installation.

• -and that around half of those are caused by poor connections!

(Just one under-tightened connector can course serious trouble in your network!).


Node/head-end

Upstream

Subscribers

Intrusion ofIntrusion of “Man-made” “Man-made”

noisenoiseoriginates fromoriginates from

• ComputersComputers

• RefrigeratorsRefrigerators

• HeatersHeaters

• ThermostatsThermostats

• TV-setsTV-sets

• Cellular phonesCellular phones

- and from lots of - and from lots of

other sources! other sources!

Noise and unwanted signals will be added from all parts of the network.

Noise from just one singlesubscriber can block the

return path system completely!

Upstream blocked

Node/head-end


“No chain is stronger than the weakest link”- and the weakest

links in a CATV network?

Connections...

- and there are thousands of them!


Let’s take a look at the most frequent connection

problems...


This is an example of a screw-on connector and a cable which have been exposed to salty moisture for just 300 hours:

Heavy corrosion

Metal in the cable is close

to disappearing!


- and the results of corrosion:

• Poor screening

• Poor return loss

This will lead to..

• Signal egress & ingress

• Intermodulation distortion

• Ghost pictures

• Loss of return path data

• Loss of forward signals

• Blocking at the node

• System downtime

• Expensive repair costs


Let’s take a look at PIM - Passive Intermodulation

(CPID - Common Path Intermodulation Distortion)• Moisture creates a layer of oxide between two different layers of metal (like a sandwich: Metal- Oxide-Metal).

• Oxidation creates a semiconductor effect (like rectifier diodes).

• Diodes act naturally as frequency mixers and multipliers.


- and furthermore on PIM...

• Carriers present in the network will be mixed and multiplied by the sum and difference.

• All these “new” created and unwanted carriers (intermodulation) will appear at more or less unpredictable frequencies.

• PIM will be more “visible” below the FM-radio band (return path range) due to lower cable attenuation!


PIM - Passive Intermodulation - schematic

Two connector parts (or cable/connector parts)

Mixing of carriers and frequency

multiplication create many “new” carriers

(PIM).

Occurrence of diode effect through oxidation


PIM, return loss and ingress problems grow at low frequencies (in return path band)...

• Cable attenuation is low (negligible). Almost no attenuation of reflected carriers caused by poor return loss.

• Frequency difference products (PIM) - caused by corrosion, are typically generated at low frequencies. Disturbance occurs in the return band.

• Considerable decrease in cable screening attenuation below 30 MHz. Extensive risk for ingress of unwanted signals and noise. Radiation will increase with poor return loss.

What happens?

Page 0655 0655 Text-TV Cabelcon Connectors Monday 18. October 1999

Poor return Loss...

AmplifierCoaxial Cable

Corroded orbadly installed

connection

Amplifierw/return path

Reflected signals + upstream (return path)

Forward signal Increased radiation

Reflections andloss of wanted

signals

Increased bit error rateand loss of data or

transmission speed!


How can we prevent or minimise problems in the return path

band?First of all through...

• Use of quality connectors

• Use of the right type of connector for your application.

• Use of quality cables with a high degree of screening.

• Proper installation practices. Let’s see some more examples...

Two different types of crimp connectors - both

manu-factured by Cabelcon - are mounted

on a piece of cable.

Both have been exposed to salty moisture for 300

hours in a chamber.

Page 0660 0660 Text-TV Cabelcon Connectors Monday 18. October 1999

The result after inspection...

This is a standardcrimp connector for

indoor use

- and this is a moisture proof type

for outdoor use!

Darkened copper foiland braid. A pre stageto corrosion - throughingress of moisture.

- You can see the difference!

Poor return loss &PIM will sooner or lateroccur after a certain time with corrosion

- while the cable installed with our

moisture proof typeremains unaffected!


- and the same result can be seen on an UltraSeal™

compression connector


- this applies to connections at all levels...

- from the smallest drop connectors...

- to the bigger trunk connectors.


Precise installation is important!

An example...


Two cables - one prepared with a special tool, while the other one was stripped in the old fashion way, using

a tube cutter.

Visible difference: The outer conductor was

2 mm too short on the “hand stripped” cable

Ordinary tube cutter Special preparation tool


The result after installation and test...

Measured return loss was two dB worse on the “tube cutter” stripped cable/connector.

“Just two dB? ” It could easily be more than two dB in each connector all the way from head-end to subscriber!


Preparation tools

• Preparation tools - especially designed for the combination of your cables and connectors - will ensure a precise installation and...

• Prevent or minimise return path problems in your network.


Finally some advise...

• Do not use screw-on connectors for professional applications.

• Choose the right type of connectors for your applications.

• Use moisture proof types (or heathshrink tube) for outdoor installations.

• Read and follow the manufacturers instructions for proper cable preparation and installation of your connectors.

• Use appropriate preparation tools - when available - for your connectors/cables to ease installation and to ensure optimal performance of your network.


If you have any questions or require more information...

- please visit our stand no. 438

This presentation can be downloaded from

www.cabelcon.dk/ecc99.htm

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