Mobile Linear Amplifier Selection & Setup
Before selecting a linear amplifier several things must be weighed. First they are illegal to use on CB radio.
You should research the decision carefully before taking the plunge into this very costly facet of the hobby.
This article includes some facts that I hope will help you make the right choice. Adding more power will give
you increased range, but it may not be what you're expecting. Sometimes using what you have efficiently
will give you the results you're looking for.
Here are some questions you need to answer first:
Is my radio peaked?
A peaked CB radio will do 6-8 AM and 18-20 watts SSB.
Is it a 12 or 25 watt radio?
An export type will do 10-12 AM and 35-45 watts SSB.
Where is my antenna mounted?
A centrally located antenna on the roof is best.
What is it's power rating?
An antenna should be capable of twice the power used.
How efficient is it?
The most efficient antenna is the 102" whip.
Do I have a quality amplified mic?
Astatic makes the best power mics.
Does the radio have speech processing?
A good speech processor raises you're average audio.
Do I receive farther than I transmit?
There's no sense transmitting farther than you receive.
How noisy is my receive?
Filtering and a good antenna can help here.
What size alternator Is In my car?
A 250 watt amp will draw 20 Amps. A 500 - 40 Amps.
Is there space for good air circulation for an amp?
Ventilation is very important for the life of an amplifier.
Remember the formula for power verses gain in the Proper Power & Modulation Adjustment article? Every
time you double you transmission power the signal increase at the other parties receiver goes up 3db.
That's 1/2 of 1 S-unit, so the largest gain is from 4 watts to 250 watts. This jump would give you a 18db gain
or 3 S-units. To get another 3 S-unit gain you'd need to put out 16,000 watts. That's right 16 Kilowatts to
gain 3 more S- units! Now you can see where efficiency comes into play, because costs can add up. Right
off I'd guess it would cost at least $60 for the trailer hitch to pull the $10,000.00 generator needed to supply
the $8,000.00 linear amp. Then you have other incidentals like wiring, ground strapping, computer shielding,
20 KW antenna system. And then you wonder, will this interfere with my ABS system? After all it would be
nice to have the ability to stop with this large investment on board.
This is a ridiculous scenario, but in reality going power happy does get crazy. Your gain for the dollar ratio
Below are two graphs. The one on the left is a fictional graph reflecting what the average radio operator
thinks happens when they run power. The one on the right is a true representation of power verses gain.
These are the sad facts. As you increase output power input supply current is required. This means a large
alternator and heavy gauge wire from the battery to the amp. And that Radio Shack antenna must go. They
would never manufacture an antenna that would allow much more than the legal limit on CB.
You've probably heard wattage isn't always the answer. True most of us want to communicate. That's a two
way street. We need to hear as well as get out. One of the most important things that most of us don't
address is noise picked up by the receiver. This could consist of ignition, alternator, computer, electric fan
and or electric fuel pump noise. Running the radio power cord directly to the battery may help with some
noise and will increase power to the radio. Antenna selection can help greatly. A shunt fed antenna such as
the Wilson base load series antennas reduce or eliminate noise in almost all cases. In case your wondering,
the K-40 antenna isn't shunt fed and won't help in the elimination of noise. If you're experiencing excessive
noise, find a friend with a Wilson base load antenna and try it on your vehicle. If you still have a problem
there are filters available that are designed for these specific interference problems and are covered in the
If you've decided to buy an amplifier, you have your work cut out for you. As I mentioned earlier they are
illegal for CB. In fact the broad band low drive type are illegal to rent sell or lease in this country ham license
or not. If you're a licensed ham operator you can build your own and use it on the allocated amateur bands.
Therefore it will be hard to find anyone that will talk to you on the subject of purchasing one. Without
mentioning the company name, the best amplifiers have a built in low pass and other filtering with an
adjustable sideband delay on the rear panel. Besides, you can't go on name alone, there are many garage
and basement operations putting the same name on their inferior products. The low pass filter is very
important in filtering the first harmonic. These broad band amps put out a great deal of spurious emissions.
Without the filtering you will be attracting attention from who knows where. These emissions will also make
your antenna match look bad and could cause damage. The low pass filter can be added externally at the
antenna output of the amp. MTI has one that will do fine. It's the LM-TVX2 and the MSRP is $37.95. More
on MTI in the next article.
The above mentioned no name amplifier is a true class AB amplifier not a class C unit. Class C is good for
AM, but unless you want to sound as if you're talking with your nose pinched on sideband you want class
AB. A quality amplifier cost more to manufacture, with price driving the market these days, almost all
manufacturers have cut all the non essential parts required to show power on the meter. If it reads power on
the meter they've done their job. These guys don't care how long it lasts. If it breaks, where do you return it?
Besides they rely on the operator not to know what their doing. Remember the cheap units don't have
filtering and will show a bad match on a tuned antenna. The paperwork will have warnings and disclaimers
on running with a bad match, so when they break the poor consumers take the blame. They have it
covered. As they say buyer beware!
There are high drive and low drive amps. If you have a radio that does only 18-20 watts on sideband you
want a low drive amp. If you have a radio capable of up to 45 watts you can use a high drive or a low drive if
you have adjustable power or turn the output down to drive the amp properly. On a low drive amp of 175 to
250 watts in the high stage the radio output should be set at no more than 18 PEP sideband. On AM the
carrier of the radio should be set to drive the amp at 1/3 the PEP rating or approximately 60 to 85 watts
dead key. The peak swing is what's going to make you heard! A lower dead key will increase the modulation
and give the appearance of a more powerful signal. A properly tuned and installed radio/amp combination
should sound good at close range and in the distance. Only if you're parked next to the other operator you
may sound lousy by overloading their receive and distorting the receive of their radio. I'm sure you've heard,
"kickers only sound good in the distance. It's only true of poor quality or improperly installed units.
Amplifiers of up to 250 watts should be wired directly to the positive and negative terminals of the battery
with #10 wire for runs up to 12 feet and #8 for longer runs. I recommend brass battery post extenders as
always. A #10 quick disconnect is a good idea so you won't have to cut wires to remove the unit if need be.
Don't forget an inline fuse or circuit breaker on the positive lead at the battery. (BCB has wire, quick
disconnects, inline fuse holders and both types of battery post extenders in stock.)
Find a mounting location that will allow air flow to the heatsink. Don't install it in the glove box or in a closed
console. Under the front seat is a good possibility. Run a braided grounding strap from the case of the amp
to a close chassis ground. You can use the braided shield from a spare piece of coax cable.
In connecting the radio to the amplifier there are two lengths of cable that I recommend. If the amp is
mounted to or close to the radio, use a I foot or less piece of coax. If one foot of cable won't do it use 1/2
wave length multiples of cable. Refer to the earlier article on coax for the formula.
SWR readings are done with the amplifier in line. Connect the meter input coax to the antenna output of the
amp. If you connect it before the amp your reading will only be the match between the radio and amp when
you turn on the power. The important match is the antenna. First check and set the match with the amp off.
If there are any problems it's best to find out with low power. The transistors in the amp are expensive and
will quickly fail with an extreme mismatch. If all is well, switch the amp on and re-calibrate the meter. The
match may go up a bit but a 2:1 is OK. If your match goes up more than that try a low pass filter.
Different power levels to me are bells and whistles that I never used, if you need power use it. If you don't,
turn it off. Amplifiers are available in what they call 2, 3 and 4 stage. This means 2, 3 or 4 power levels.
Low/High, Low/Med/High, or Low/.N4ed/High/Max. They have a selectable attenuator on the input that
reduce the drive from your radio into the amp. Most people think the more the better. Almost all amps are bi-
amp. This is that they have a switchable receive preamp. Most of them pull in more noise than signal
making them useless. But this also depends on the radio and installation. The unit I mentioned earlier in this
article has a sideband delay adjustment on the rear of the unit. This can be adjusted for different individuals.
Some operators speak quickly and don't take long pauses during transmissions. Others take frequent
pauses. This adjustment allows you to tailor the delay to your individual radio habits.
Following these basic rules and taking the time to do a quality job will insure great long lasting results. If you
already have a linear, check and see if everything is set up as described earlier. You may improve the
sound and range of an existing station.
In This Issue
© CB World Informer Network 1996 - 2023 Worldwide Rights Reserved
Review Of The Chipswitch
How To Make The Best Solder Connections
Slick Tricks On Microphone Wiring
Proper Base Station & Mobile Grounding
Advertising Claims...Smoke And Mirrors?
Comparison of Cobra 2010 to 2000
Power & Modulation Adjustments
New DF 10,000 Low Pass Filter
Coax Types & Lengths
Linear Amp Selection &Setup
Mobile Radio Interference
New Product Review: Astatic's EchoMax 2000
Channel Kit For PC-122 & Cobra 146-GTL
Did You Know?
Increasing Interest In CB Rumored
What's Happened To Organized CB
Santa's Best CB Gift List
Bob's CB Reopens
New Product: Midland 79-290 AM/SSB Mobile
Swap & Sell
New Product: New Anttron 305 Base Antenna
What's Happening To CB?
CBWI Proposal To Improve 11 Meters
Cobra/Uniden SSB Chassis Mods.
Review Of Midland 79-290 AM/SSB Mobile
Cobra/Uniden SSB Chassis Mod UPDATE
President Jackson Unlocked Clarifier Mod.
Cobra 148 & Uniden GrantXL Clarifier Mod.
Cobra 142GTL & Uniden Washington Clarifier
Uniden Grant Unlocked Clarifier Mod.
Uniden PCI22 PRO SSB Clarifier Mod.
Review Of The Northstar DX880HL
Big Bust At The Consumer Electronics Show
Bob's CB Has Opened
The New Mongoose Model 450 Review
Wilson Antenna Tests The Trucker 5000
A Company With Interference Solutions
Solving Telephone RF Interference
Lowpass Filters: What, Where, And How
Using Highpass Filters For TVI
How To Conduct A Noise Audit
Modern Do-It-Yourself Grounding Techniques
Using Water Pipes For RF Grounding
Using Water Pipes For RF Grounding
The New Emperor TS-3010 Review
Grounding Coaxial Cable Shields
Modern Lightning Protection - RF Entry Ports
Modern Lightning Protection - AC Power Lines
Modern Lightning Protection - Control Lines
Modern Lightning Arrestors - Polyphaser VS I.C.E.
Modern Lightning Arrestors - Alpha Delta VS I.C.E.
Modern Lightning Arrestors - Cushcraft VS I.C.E.
Galaxy DX 2547 Reveiw
Inside The DX 2547
DX 2547 Channel Mod
DX 2547 Clarifier Mod
DX 2547 Photos
DX 2547 Manual Excerpts
The Anttron Story
Anttron 305 Revisited
New Antrron Products
Aries A-SWR 460 Digital Meter
Barjan Buys Wilson Antenna
Wilson Electronic In Cell Phone Market
First Web Issue
Help Get The Word Out
Sneak Preview: The New Maverick A24
Maverick A24 Front Panel Controls
Inside The Magnum Maverick A24
Barjan Buys Francis Antenna
Wilson Antenna, 1 Year After Barjan Buyout
Solarcon I-Max 2000
False Performance Claims
CAUTION: Don't Burn Out That Radio
Magnum's Filtered Power Cord
Dragon Super Heavy Duty SO-239 Stud
CBWI...Give Us Your Opinion
Reveiw Of The RCI 2950DX
RCI 2950DX Image Rejection Modification
RCI 2950DX Coversion & Clarifier Mods
RCI 2950DX Photos
RCI 2950DX Board Component Layout
RCI 2950DX Adjustment Layout
RM-9807: Petition To Remove 155 Mile Limit
Slip-Seat Radio Box
RF Limited UTB-1 Adjustable Talkback Board
A Message From The Editor
Review Of The General Lee
General Lee Conversion
General Lee Tune-Up
Genral Lee Pot. Adjustments
Proposal For Citizens Radio Network
RF Limited EC-2018 Turbo Echo Mic
RF Limited EC-2018XTR Xtreme Echo Mic
RF Limited TRB-1 Turbo Echo Board
Santas CB Gift List
Review: RCI 6900F TB 10 Meter Transceiver
RCI 6900F TB Frequency & Clarifier Mods
RCI6900F TB Tune-Up & PCB Adj. Locations
RCI 6900F TB Photo Gallery
UPDATE: Maverick A24 Transceiver
Texas Ranger SRA-158 Stock Mic
Astatic's Final Edition D-104 Silver Eagle
Firestik's All American Limited Edition Antennas
Uniden PC 68XL Turbo 121 Combo From Mexico
The Cobra 29 Night Watch Classic
Cobra XL 450 Amplifier From Mexico
Review: The Magnum 357DX
Magnum 357DX Photo Shoot
Magnum 357DX Conversions
Magnum 357DX Adjustments
MD-4 External S/RF Meter
Adding MD-4 To The Magnum 357DX
Adding MD-4 To Other Radios
PanaVise Pedesal Mount
A Little History On The CCC People
AR-3500 Operating Manual
AR-3300 & AR-3500 Photos
Maverick A24 Technical Bulletin
Super Star Silver Salute Specifications
Magnum Delta Force 2002 Conversion
Top Gun 56 Mic
Top Gun 56 Story
Top Gun 56 Audio Test
QUAD-5 10 Meter Transceiver
QUAD-5 Magnified Photo
QUAD-5 Operator's Manual
QUAD-5 Photo Gallery
Top Gun SP-1a Speech Processor
DAS Acquires Turner
RCI Move Manufacturing
TelePost Meter & Monitors
LP-100 Vector Power/SWR Meter
LP-500 Station Monitor
LP-700 Station Monitor