Computer Help
 Contact
 Search
 
  
    

Jeep JK Lift Kits
Black Diamond JK Lift Kits
Black Diamond PR
Poly Performance JK Lifts
Teraflex Jeep JK Kits
Skyjacker JK Kits
Rancho Jeep JK Kits

Rubicon Express JK Kits

ATV World
ATV Clubs
ATV Tire FAQs
ATV Tire Mounting
Cool ATV Products
LiteFoot Track Sys
ATV Lift Installs
Quad Tire Reviews
ATV Laws By State
ATV Repair
ATV Manuals

Jeep Project CJ-7

An ongoing Budgeted Rebuild/Build up of a Rock
Crawling Machine.

Offroaders Guide to Gearing up for Offroad
From Basic Equipment to Well Equipped.  An extensive list guide to help you prepare your vehicle for the offroad.


Trailering Safety and Trailer Hitch Information


Off-Road Truck Driving Techniques and Safety

25 Top To Do Tips Before Going Offroad
 

Troubled
Computer?

Got Pop-ups
Spyware & Viruses?
Offroaders.com feels your pain. Let our Geeks help you...
RalphtheGeek.com

 


Rausch Creek
Off-Road Park

 

Jeep Central
From Jeep History to Tech Specs and Projects.  This section is all about Jeeps.
Jeep Technical Info
Engines
Transmissions
Transfercases
Axles
Engine Swaps

Installing 23,000 Volt Offroad Lights


Onboard Air
Converting a York
AC Compressor
to Pump Air

What are HID Lights?

Onboard Air
Converting a York
AC Compressor
to Pump Air

Warn 9500i Winch Installation

Warn X8000i
Winch Installation

 

HEI Ignition
Installation & Review

Lockers, Limited Slips &
other Differentials Explained

 

 

 

Wheeling in the Valley of the Ferns

1.jpg (70086 bytes)
Tellico North Carolina


Paragon Adventure Park
Rock Krawl

Thousands more photos here..

 
 

 

 

 

How does a CB radio
antenna work and why
does it need to be tuned?
 

A Citizen Band or "CB" radio as it is widely known, is a radio transceiver for two way communication, transmitting and receiving, over a CB radio antenna.  The job of the antenna on a CB radio system is two-fold.  First it captures inbound radio-frequency signals which are then converted into electrical signals by the CB's receiver.  Second, it converts outbound electrical signals coming from the transmitter and converts them into radio-frequency signals that are then broadcasted onto the air waves, hopefully to another receiving CB radio.  This is the transmitting function of a CB radio.  It is during the transmitting function of a CB radio that proper tuning of the antenna becomes important.

This is due to the fact that an antenna is radiating radio-frequency signals of a specific wavelength.  A properly tuned antenna will have a length that will accurately match the radio frequencies wavelength it is transmitting.

Determining the proper length of the antenna can be done using this formula:

Wavelength feet = 984 / frequency megahertz

Citizens' Band (CB) frequencies begin at 25.01 MHz.  A full wavelength antenna would be slightly longer than 39.34 feet tall.  For mobile purposes, the height of a full wavelength antenna would be impractical.  So it is common practice to use antennas that are a fraction of the full wavelength.  1/8, 1/4, 5/8, and 1/2 are all commonly used wavelengths for antennas.  For mobile CB antennas the quarter wave antenna is just under 10 feet long and take to form of the common whip antenna.

The dilemma is that there are 40 channels on today's citizen band transceivers.  Each channel is on a different frequency, thus requiring a different antenna length to exactly match each frequency.  However, a separate antenna for each frequency is simply not practical so a compromise must be made and antenna manufacturers design antenna lengths from the middle of the CB's 40 channel frequency range. 

However with any compromise, there are tradeoffs and you have to adjust the Standing Wave Ratio or SWR of the antenna and wire until the SWR is acceptable.  The antenna and antenna feed line have what is called characteristic impedance, or a measure of resistance to the current flow through the wire and out the antenna. 

When a transmitter is connected to an antenna by a feed line, the impedance of the antenna and feed line must match exactly for maximum energy transfer from the feed line to the antenna to be possible.

In the best possible scenario, there would be a perfect match between antenna and the feed line where there would be a 100% conversion of electrical energy (sent from the CB to the antenna) into radio wave energy and radiated out into the atmosphere.   When perfectly matched, the SWR measures 1:1 and the antenna is maximizing it's potential output.

In the less than ideal scenario, a portion of the electrical energy (from the CB) is not converted into radio wave energy and instead is reflected back down the feed line and into the CB radio.  This energy reflected back from the antenna creates standing waves of electrical energy in the antenna wire and in turn can cause damage to the radio circuitry.  

When tuning the SWR of an antenna, an SWR meter is attached between the CB radio and the antenna feed line.  SWR meters vary and some allow the meter to generate a signal on different channels while other SWR meters use the CB by keying up the microphone to generate a signal.  As a signal is generated, the SWR meter is observed. 

Ideally its best to tune your antenna for the channels that you use most if you typically only use one or a few channels.  Otherwise use a broader test across the full range of 40 channels.   If the SWR never goes above 1.5:1, then your antenna is well tuned.  If the SWR does go above 1.5:1, then test the SWR on the lower channels such as 1 through 5 and compare those SWR reading with the upper channels such as 35 through 40.  If the SWR is greater on the lower channels then your antenna is too short and needs to be lengthened using the antennas height adjustment.  Make small adjustments and retest.  If the SWR is greater on the higher channels, then gradually shorten the antenna and retest with each small adjustment.  When adjusting in either direction, if the SWR begins to test greater, reverse the adjustment to find the "sweet spot".

Keep in mind that the electrical ground of the antenna, the shape of the vehicle including open doors, hoods and hatches as well as the location of the antenna on the vehicle, all play a part in proper adjustment.  Test with the door and hatches closed and experiment with different mounting locations of the antenna.

Last, be sure to read and understand the instructions of the SWR meter as well as the antenna itself.  In the end, with good SWR, you'll be transmitting to your fullest potential and ensure longevity to your radio. 

 
 

Related Information:

CB Radio for the 4x4 - Installations, Adjustments , Troubleshooting, and general Information about Citzens' Band Radio

How does a CB radio antenna work and why does it need to be tuned?

How to ADJUST YOUR SWR on your CB Radio and the reason Why it should be adjusted

Adjusting SWR using the Para Dynamics SWR Meter

Antenna Size vs. Power Output

Wiring the Cobra Mic

Adjusting SWR on a CB Radio

Information About Citizens' Band Radio



Jeep Project CJ-7

An ongoing Budgeted Rebuild/Build up of a Rock Crawling Machine.

All Terrain 
Mud Terrain
Tire Reviews & Info

All Terrain
AT Tire Reviews


Mud Terrain
MT Tire Reviews

 

 

Ramp Travel Index
RTI / Ramp Travel Index What it is and how to calculate it, with and without the ramp.

Offroad Tire Info
P-Metric Tire Sizes Conversion to Inches
Tire Terminology
Wheel Terminology
How to Pick the Right
Tires for your Truck
Truck Tire Info
Tires - What Hits What Fits
  
All Terrain  Mud Terrain
Tire Reviews & Info
Mud Terrain MT Tire Reviews
All Terrain AT Tire Reviews
Super Swamper Bogger
Super Swamper SSR
Super Swamper SX
Super Swamper Vortrac
Interco IROK TSL
Super Swamper LTB
Super Swamper TSL
Super Swamper TSL Radial
Super Swamper Narrow
Interco SS-M16 Swamper
Thornbird TSl Radial
Thornbird TSl Bias
Thornbird TSL
Parnelli Jone Dirt Grip
BFGoodrich Krawler
BFGoodrich MT T/A KM
BFGoodrich MT T/A KM2
BFGoodrich AT TA KO
BFGoodrich Mud King XT
Bridgestone Dueler MT
Cooper Discoverer ST
Cooper Discoverer STT
Cooper Discoverer ST/C
Federal Couragia MT
Firestone Destination AT
Firestone Destination MT
General Grabber MT
General Grabber AT2
Green Diamond Icelander
Ground Hawg Mud Tire
Hankook Dynapro MT
Hankook Dynamic MT RT01
Hercules Terra Trac MT
Hercules Trail Digger MT
Kelly-Springfield Safari DTR
Kelly-Springfield Safari MSR
Kumho Road Venture MT
Kumho Road Venture KL71
Kumho Road Venture AT
Dick Cepek Mud Country
Dick Cepek F-C II
Dick Cepek Fun Country II
Dick Cepek Fun Country Nylon
Dick Cepek Fun Country Kevlar
Mastercraft Courser MT
Mastercraft Courser HTR
Mastercraft Courser HTR Plus
Maxxis BigHorn Radial
Maxxis Creepy Crawler
Maxxis Trepador
Maxxis Buckshot Mudder
Maxxis MA-SW
Maxxis M-8080 Mudzilla
Maxxis MT-754 Buckshot
Maxxis MT-753 Bravo
Maxxis MA-751 Bravo
Maxxis MA-S2 Marauder II
Maxxis MA-S1 Marauder
Maxxis MT-762 BigHorn
Nitto Mud Grappler
Nitto Terra Grappler
Nitto Dura Grappler
Nitto Dune Grappler
Nokian Vatiiva MT
Pit Bull Rocker Extreme
Pit Bull Maddog
Pit Bull Growler
Goodyear Wrangler MT/R
Pro Comp Xterrain
Pro Comp All Terrain
Pro Comp Mud Terrain
Pro Comp Xtreme AT
Pro Comp Xtreme MT
Toyo Open Country MT
TrXus Mud Terrain
TrXus STS All Terrain
Michelin LTX A/T
Michelin LTX AT2 Press
Michelin LTX AT2
Mickey Thompson MTZ
Mickey Thompson MTX
Mickey Thompson Baja Claw Radial
Mickey Thompson Baja Claw Bias
Mickey Thompson Baja Crusher
Mickey Thompson Baja ATZ Radial SLT
Competition Claw
Dunlop Mud Rover
Federal Couragia M/T
Nitto Dura Grappler
Yokohama Geolandar
  
Dick Cepek's 2008 F-250 Super Duty Project Vehicle Project CRUSHER
 
Mud Tire Reviews
Product Reviews
Tire Reviews
 
  
 
ATV Tire Index
Carlisle 489 Titan
Dunlop Quadmax
Dunlop Quadmax Sport
Quadmax Sport Development
Highlifter Outlaw
ITP Holeshot
ITP Holeshot MX
ITP Holeshot ATR
ITP Holeshot XC
ITP Holeshot XCR
ITP Holeshot MXR
ITP Holeshot XCT
ITP Mud Lite
ITP Mud Lite XTR
ITP Sandstar
Kenda K538 Executioner
Tubeless Bearclaw K299
Kenda Klaw K532
Kenda Klaw K533
Kenda K534 Sand Gecko
Maxxis M961/M962 Mud Bug
Maxxis Rooster Paddle Tire
Maxxis M917/M918 Bighorn
Maxxis M966 Mudzilla
Super Swamper TSL ATV
Super Swamper TSL Vampire
Super Swamper Vampire EDL
Swamp Lite ATV Tires
 
ATV Tire FAQs
ATV Tire Mounting
ATV / Quad Links
 
Quad Tire Reviews Index

 


Off-Road Lights
by LightForce Product Review / Installation.
from Off-Road Lights

 


Jeep Dana 300 TeraLow - 4:1 Gearset for the Dana 300 Transfer Case

Jeep Trans Swap
T-18A Transmission Rebuild & Short Shaft Conversion
  


Black Diamond Suspension Lift install for CJ-7

 

From the
Department of Cheap   Tricks and Useful Tips

  
Ultra-Cool Hand Throttle for Free!

Jeep V8 Swap Tips

The Exploding Clutch

Radiator Protection using 6 bucks worth of material

Cracked Under Pressure - Fixing a smashed fingernail

A Cheap, effective alternative to undercoating

Home-built Saginaw Gearbox Brace for the cost of lunch!

Ammo Box Storage - Mounting Them for Quick Disconnect

Home-built Serious Skid-Plate protection for the Oil Pan for under 20 bucks!