Date:         Mon, 4 Dec 2000 09:28:20 -0800
Reply-To:     pensioner <al_knoll@PACBELL.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         pensioner <al_knoll@PACBELL.NET>
Subject:      CB Power .
Content-type: text/plain; charset="iso-8859-1"

Hi Volks,

CB power per the FCC is the power delivered to the final power amplifier not
the measured RF power out of the transmitter.  That's why a 5W max rated CB
transceiver delivers less than 5W to the antenna.  How much power goes to
the antenna is determined by the "matching" between the RF output
characteristics of the final and the characteristics of the cable and
antenna.  About the best the user can do is to achieve what is called a
minimum standing wave ratio (SWR) at or near the favorite operating
frequency.  This tuning ensures maximum power delivered to the antenna.

CB is amplitude modulated, that is to say the "voice" is carried in changes
to the amplitude of the signal.  Ensuring 100% modulation or therabouts will
give you maximum "talk power" available to the final amplifier.  Ensuring
the best possible match to the characteristics of the antenna will ensure as
much "talk power" as possible is radiated from the antenna.

 The characteristics of the antenna determine how this power is radiated
spatially.  A 3db gain antenna has a radiation pattern that has 3db gain in
one plane and a corresponding reduction of radiation in the other planes.
Rather like a floodlight versus spotlight.

Here as in many other engineering compromises, TANSTAAFL (no free lunch).
If you'f like the convenience of a folding antenna that neatly hides in the
rain gutter you trade that for radiated "talk power".  A "base loaded" 5/8
Wave whip (antenna) on a good ground plane (the roof) will give you about as
good performance as you can expect from any other configuration for vehicle
to vehicle and vehicle to ground based communications.

A key consideration is that the antenna is bi-directional.  The better the
antenna the better the available signal to the receiver section of the
radio.  The better the reciever section/antenna combination the better you
can receive and understand "the other guy".  A 100W linear amplifier has no
significant effect on making reception better and for close communication
most "linears" "splatter" the signal across several channels and generally
overload the other guys receivers.

So for best 27Mhz/12-11M performance pick your reciever carefully, match a
good antenna (my fave is the venerable K70), use a "power mike" and a set of
headphones.  Adding additional power to the output signal buys little in
communication with a distant "5 Watt" station if you can't hear the distant
station.  Now if both stations are operating with increased transmitted
power it is a different story.

In the glory days of CB there were lots of choices of equipment and
antennas.  The choice is more limited now.

The "classic" Cobra set had an RF gain control and a delta tuning for the
reciever section.  It also had a very fine output final.  RatShack has a
similar reincarnation currently and I believe the Cobra line is still
available.

For close ~1mi inter vehicular communications the Family Radio Service VHF
hand helds like the Motorola Talkabout and others is a much better solution
than CB.

cheers, (73s)

pensioner