VHF / UHF Antennas and Coaxial Cable - PowerPoint PPT Presentation

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VHF / UHF Antennas and Coaxial Cable

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The importance of knowing what you are using between the antenna and the radio. ... Goals and Objectives Goal #1 Learn some basics about antenna gain. – PowerPoint PPT presentation

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Title: VHF / UHF Antennas and Coaxial Cable


1
VHF / UHF Antennas and Coaxial Cable What is
your ERP ???
KARS Net Discussion Tuesday, 23 August 2011
  • Presented by
  • Del Partridge, W5QQ

2
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.

3
Goals and Objectives
  • Goal 1
  • Learn some basics about antenna gain.
  • Goal 2
  • Learn a little about the effect that different
    types of coaxial cable have on overall antenna
    performance.
  • Objective
  • To become more familiar coaxial cable types and
    their effect on overall station performance.

4
Vocabulary
  • 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.

5
Vocabulary
  • 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.

6
Topic One
  • How coaxial cable effects antenna performance.
  • In this example we will look at different types
    of coaxial cable and coaxial cable loss.
  • We will then examine the Effective Radiated Power
    (ERP) from a unity gain antenna using different
    types of coax.
  • Because coaxial cable loss goes up as frequency
    goes up we will show examples of the phenomena at
    both 2 meters and 70 centimeters.

7
Topic One
  • As 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 11.
  • 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.

8
Topic One
  •  

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.
9
Topic 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.

10
Topic Two
  • .

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.
11
Topic Three
  • The 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.

12
Summary
  • 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.

13
Where 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 usedhttp//www.davisrf.com/
    http//www.thewireman.com/ http//www.radioworks.
    com/hpmain.html
  • Where to read about Isotropic antennashttp//en.
    wikipedia.org/wiki/Isotropic_radiatorhttp//www.s
    meter.net/daily-facts/9/fact15.phphttp//www.qsl.
    net/ve3mcf/elecraft_reflect/Antenna_Measurements.t
    xt
  • 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.
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