1 National Urban Search & Rescue Response System Communications Specialist Course Communications Specialist Course Skill 3 Unit 2: RF Cables and Meters.

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National Urban Search & Rescue Response System

Communications Specialist Course


Skill 3 Unit 2:

RF Cables and Meters

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Unit Objective

Upon completion of this unit, you will be able to

Describe RF coaxial cables and connectors and their installation and care

Test an installed transmitter, coaxial cable, and antenna with a wattmeter for proper operation

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Enabling Objectives

Describe RF coaxial cables and connectors

Describe the installation and care of coaxial cables and connectors

Describe the use of a wattmeter


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RF Coaxial Cables

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Coaxial Cable Construction

Center Conductor

Dielectric

Shield (s)

Outer cover

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RF Coaxial Cables

Preassembled in the cache with connectors installed

Cable specifications include the loss/ft in decibels (dB)

The longer the cable the more power loss (Attenuation)

Protect cables from damage

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RF Loss 25 watt base station

0 dBno loss 25 watts

3 dBx.50 12.5 watts

6 dBx.25 6.3 watts

10 dB x.10 2.5 watts

15 dB x.032 .79 watt

20 dB x.01 .25 watt

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Coax Cable Loss 420 Mhz

RG 58 10.4 dB/ 100 Ft

RG 213 4.7 dB/ 100 Ft

LMR400 2.6 dB/ 100 Ft

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RF Connectors Must match the cable

Use N type connectors when possible

Keep connectors clean and dry

Seal connections from weather

Protect connectors from damage

Have spare connectors, adapters and installation tools

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RF Wattmeter

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Wattmeter Set Up

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Checking the RF Power Turn off the Transmitter

Install the wattmeter in the Coax at the transmitter

Start at 500 watts and FWD

Key the transmitter

Lower the range until a useable reading is on the scale – record reading de-key the transmitter

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Checking the RF power (continued)

Switch to REV

Key the transmitter

If necessary lower the range to get a useable reading on the scale

Reflected power should be 10% or less than the Forward power reading

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Causes of High RF Power Reflection Mismatched or damaged antenna

Damaged Coax or connector

Shorted Coax or connector

Debris or water in coax or connectors

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Review

Coax Cable Construction

Center conductor

Dielectric

Shield

Outer cover

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Review (continued)

The longer the RF cable the more power loss

3 dB loss = 50% loss

10 dB loss = 90% loss

Protect RF cables from damage

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Review (continued)

RF Connectors

Keep clean and dry

Protect from damage

Seal connections from moisture

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Review (continued)

RF Wattmeter

FWD measures RF power from transmitter to coax and antenna

REV measures RF power reflected back to transmitter

REV power should be less than 10% of FWD reading

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Review (continued)

Common causes for high reflected wattage

Mismatched or damaged antenna

Damaged or shorted coax or connector

Debris or water in connector or coax

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Unit Summary

Describe RF coaxial cables and connectors

Describe the installation and care of coaxial cables and connectors

Describe the use of a wattmeter


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Unit Evaluation

Please fill out the evaluation form for this unit

1 National Urban Search & Rescue Response System Communications Specialist Course Communications Specialist Course Skill 3 Unit 2: RF Cables and Meters.

Documents

transmitter slide

rf cables

watt slide

ft slide

damage slide

forward power reading

installation tools slide

proper operation slide