VHF / UHF Antennas and VHF / UHF Antennas and Coaxial Cable – Coaxial Cable – What is your What is your ERP ???ERP ???

Presented by:Del Partridge, W5QQ

KARS Net Discussion – Tuesday, 23 August 2011

Introduction Introduction

How coaxial cable effects overall station performance.

Some different types of coaxial cable and how they effect power output at 2 meters and 70 centimeters.

The importance of knowing what you are using between the antenna and the radio.

Goals and ObjectivesGoals and Objectives

Goal #11. Learn some basics about antenna gain.Goal #21. Learn a little about the effect that different

types of coaxial cable have on overall antenna performance.

Objective: 1. To become more familiar coaxial cable types

and their effect on overall station performance.

VocabularyVocabulary

dbd: Used as a reference to a theoretical one half wavelength dipole in free space.

dbi: Used as a reference to a theoretical isotropic antenna in free space.

Isotropic antenna: A theoretical antenna that radiates the same level of energy in all directions when power is applied to the antenna. (Most often used antenna reference. Be careful.)

ERP: Effective Radiated Power (ERP) is the term used to describe the calculated power emitted from the antenna.

VocabularyVocabulary

The most often used antenna reference to describe antenna gain is dbi. This can be misleading.

A theoretical isotropic dipole in free space would have a gain of 2.15db over a theoretical dipole antenna with all other parameters equal. This reference, dbi, would make an antenna appear to have greater gain than an antenna referenced to dbd as a measure of gain.

Topic OneTopic One

How coaxial cable effects antenna performance.

1. In this example we will look at different types of coaxial cable and coaxial cable loss.

2. We will then examine the Effective Radiated Power (ERP) from a unity gain antenna using different types of coax.

3. Because coaxial cable loss goes up as frequency goes up we will show examples of the phenomena at both 2 meters and 70 centimeters.

Topic OneTopic OneAs an example suppose the following: You are using 100’ of Tandy RG-58 coax. Your antenna is a quarter wave vertical with

unity gain. The antenna SWR is 1:1. Your radio puts out 50 watts on 2 meters and

35 watts on 70 Centimeters. Your loss at 146 MHz is: 5.026 db and your

power out is 15.716 watts. Your loss at 446 Mhz is: 9.621 db and your

power out is 5.546 watts.

Topic OneTopic One

 Output in watts Output in watts

Coaxial Charateristic Loss in db W/50 watts Loss in db W/35 wattsCable Type Impedance (Zo) at 2 Mtrs input power at 70 Cm input power

RG-58U 50 5.03 15.72 9.62 3.89RG-8X 50 4.23 18.88 7.99 5.56RG-213 50 2.61 27.41 4.97 11.13Bury Flex 50 1.74 33.47 3.11 17.12LMR-400 50 1.50 35.42 2.68 18.09LMR-600 50 0.95 40.16 1.71 23.59

Coaxial Cable Loss per 100' at 2 meters and 70 centimeters

Note: For this example a dual band FM transceiver with 50W output on two meters and 35 W on seventy centimeters is assumed. The antenna has unity gain. In this example there are no losses except as shown in the chart above.

Topic TwoTopic Two

What would happen to the Effective Radiated power if we connected a dual band J-Pole.

For the sake of discussion we will agree that the J-Pole has a gain of 3dbd at 2 meters and a gain of 6dbd at 70 centimeters.

Topic TwoTopic Two

.

ERP ERP ERP ERPCoaxial Charateristic Loss in db Unity Gain 3dbd Loss in db Unity Gain 6dbd

Cable Type Impedance (Zo) at 2 Mtrs Vertical J-Pole at 70 cm Vertical J-Pole

RG-58U 50 5.03 15.72 31.44 9.62 3.89 15.56RG-8X 50 4.23 18.88 37.76 7.99 5.56 22.24RG-213 50 2.61 27.41 42.82 4.97 11.13 44.52Bury Flex 50 1.74 33.47 66.94 3.11 17.12 68.48LMR-400 50 1.50 35.42 70.84 2.68 18.09 72.36LMR-600 50 0.95 40.16 80.32 1.71 23.59 102.36

Effective Radiated Power - unity vs 3db & 6db antennas

Note: For example a dual band FM transceiver with 50W output on two meters and 35 W on 70 centimeters is assumed together with and assumed antenna gain on two meters of 3db and an antenna gain on seventy centimeters of 6db. In this example there are no losses except as shown in the chart above.

Topic ThreeTopic ThreeThe importance of knowing what

you are using between the radio and the antenna.

For short runs use RG 58 or RG 8X. RG-8X has less loss and a foam dielectric. Good and bad.

Up to thirty or forty feet for close in work RG 8X works.

For longer runs look to higher quality coaxial cables. The most expensive accessory in your station can

easily be cheap coaxial cable.

SummarySummary

We have discussed two antenna measurement references: dbd and dbi.

We have looked at the effect of different types of coax on ERP.

We have discussed the importance of knowing what you are putting between the radio and the antenna.

Where to Get More InformationWhere to Get More Information This site will compute coax loss and ERP for you:

http://m0ukd.com/Calculators/ERP_Calculator/index.phphttp://www.hamuniverse.com/coaxdata.html

The ARRL Amateur Radio Handbook and the ARRL Antenna Book are invaluable sources of information.Some suppliers on the Internet that I have used:http://www.davisrf.com/ http://www.thewireman.com/ http://www.radioworks.com/hpmain.html

Where to read about Isotropic antennas:http://en.wikipedia.org/wiki/Isotropic_radiatorhttp://www.smeter.net/daily-facts/9/fact15.phphttp://www.qsl.net/ve3mcf/elecraft_reflect/Antenna_Measurements.txt

The effect of SWR on power loss: http://www.wcerc.org/swrlosschart.aspThe usual disclaimers apply. I received no remuneration of any kind from any of these suppliers. I own no part of any of these companies and I offer their names only as sources that I have purchased from before.