Introduction (or Why Make Transmission Line Measurements?)

• A transmission line (or cable) transfers electrical energy from one point to another.

• Time delay and Attenuation (distortion and losses) are also important parameters for high speed busses.

Attenuation

• Lossy lines are becoming increasingly important in high speed

• Yet, there is much confusion in the industry about the origin of the losses and how to account for their effects in practical ways.

Attenuation (cont.)

• The power loss in a cable. It is due to heating loss because of conductor resistance and skin effects.

• Dielectric loss caused by poor dielectric materials.

• The total loss is expressed in decibels (dB) per unit length of cable (ratio between two amounts of power existing at two points) dB = 10 log P1/P2

Attenuation (cont.)

Attenuation (cont.)

• The most important effect arising from a lossy transmission line is rise time degradation.

• The losses behave in a way that causes higher frequency components of the signal to be attenuated more than low frequency components

RG223

-6

-5

-4

-3

-2

-1

0

1

2

3

4

6 6.5 7 7.5 8 8.5 9 9.5 10 10.5

10^ Hz

10

^ (

Att

en

ua

tio

n)

Metal DialectricRG223

K02252D

-6

-5

-4

-3

-2

-1

0

1

2

3

4

6 6.5 7 7.5 8 8.5 9 9.5 10 10.5

10^ Hz

10

^ (

Att

en

ua

tio

n)

Metal DialectricK02252d

Connectors cascade

• compare between 4 connectors cascade (1 male-male,1 male- female and 2 female- female) to 2 connectors cascade (1 female-male and 1 female-female) and 1 female- female

Cascade of connectors

1 adaptor

2 connectors

4 connectors

Attenuation [db] Vs. freq [Hz]

Cascade - conclusion

• As expected, connector in serial cause signal decrease

• While concatenate a few elements, minimize number connectors

Two cables and connector manipulation

• Cable rg58 measurement

• 2 Cables rg58 plus connector between

• Two rg58 attenuation by mathematical multiple on single cable

Two cables and connector manipulation

1 rg58 cable

2 rg58 without any connector

2 rg58 with connector

Attenuation [db] Vs. freq [Hz]

Two cables and connector manipulation conclusions

• As we can see , the multiply by 2 of the single 1m cable characters an attenuation of 2m cable.

• The lower curve present the influence of the connector .

• It’s better to use one single long cable than two cascade of short cables.

Good/Bad cables, connectors and relationship

• Rg58 with / without connectors

• Sucoflex100 (8274/4E) with/without connectors.

• Substrate a different and comparison

Good/Bad cables, connectors and relationship

Good cable

2 cable + connector

Bad cable

Bad cable + connector

Attenuation [db] Vs. freq [Hz]

Manipulation on the couple of curves above ( substract the attenuation ,show that there is no relationship between good cale + connector VS. bad cable + connector.

Attenuation [db] Vs. freq [Hz]

Conclusion-

• The quality of the cable does not relate to the connector influence,

• The attenuation behaves in serial effect.

• Assumption – the gap between the diff curve result from measure mistakes.

Elements location

• cable – connector – cable

• connector –cable – cable

• cable – cable – connector

Location of the elements in cascade

Attenuation [db] Vs. freq [Hz]

element location - conclusions

• There has no different in arrangement of elements

• As known , VNA measures and calculates the DUT (passive elements) between the calibration edges as whole component and ignore the inner order.

Measurement sensitivity

• Flexibility.

• Connection tightening between elements.

Flexibility based on the vendor parameters .

Little radius

Big radius

Attenuation [db] Vs. freq [Hz]

Connection tightening between elements

Tight connection with Newton key

Tight connection with hand

Weakly connection

Attenuation [db] Vs. freq [Hz]