Craig,
A few things to consider on installing CB equipement, in the "CB glory
days" I worked for Lafayette Radio repairing and installing CB geer and
can answer your questions.
1. Someone asked about the "dual antennas" mounted on their mirrors.
Dauls were primarilly installed on vehicles that wanted to use their CB
rig on the open highway. A vertically polorized mast style antenna has
a 360 degree horizontally equal transmission pattern, this means you can
"get out" the same distance in all directions.
Duals double their output foreward and backward of the vehicle because
the transmission signal is split between the 2 masts which sends a
double signal front and back but a half signal side to side. The inside
radiation is cancelled which forces the "squashed" transmission pattern.
The problem with duals are they are directional and can loose contact if
the vehicle turns. They are also a #@\?! to tune. If a "good Buddy"
wanted the best antenna, I would recoment a 104" whip style antenna
mounted on the roof, of course this looked a bit weird but hey, he's the
one that wants the "big ears"!
2. Mounting location will effect the transmission of the antenna. The
roof of the vehicle acts as an artificial ground up 10 feet in the air
and allows the signal to multiply its output by "bouncing " the signal
off the roof. This is called "ground plaining" and is a good thing. If
you mount the antenna on the side of the coach, your output on that side
will be noticablly lower because the antenna cannot take advantage of
bouncing its signal off of the roof in that direction. The best
mounting location for the antenna is in the middle of the metallic
(aluminum) of the roof.
3. Even more important than the style or location of the antenna is
"tuning" the antenna to the unit you are using. The "SWR's" must be set
for optimum output. If your unit does not communicate well as you move
away, chances are your SWR (standing wave ratio) is over 3 to 1. Get
the system tuned!
- ----------------------------
For those who have nothing better to do, I'll tell you about SWR's.
"Standing wave ratio", SWR is a spec. which relates the amout of
transmission that leaves the unit to the amount of signal that leaves
the antenna and radiates into the atmosphere. It actually is a value
that states the impedance (alternating current resistance) match of the
output transister, coax cable & mast length of the system.
A spec. of 1 to 1 means all of the signal that leaves the set leaves the
antenna and you have no "standing waves". If your signal specs. at 3 to
1 or higher, you probobly cant transmitt past the car in front of you!
This spec. is sensitive and as much as 1/16" mast length will be the
difference between good and bad output.
Be the hero of your club, invest $20 and pick up an SWR meter from Radio
Shack. Chances are everyone that has a CB has not had their SWR's
checked and you can do them a great service at a rally by doing a SWR
check for the group! Today, CB radios are not taken very seriously by
installers and they have no idea how important SWR's are to the
performance os the rig.
If you want to pick up a meter, I would be happy to talk you through the
adjustment procedure. I will be sure to bring my meter to Marion for
those who would like me to set theirs up. Charge will be 1 beer!
Let me know if you have any more questions.
Jim Bounds
www.gmccoop.com
>
> > -----Original Message-----
> > From: owner-gmcmotorhome
> > [mailto
wner-gmcmotorhome]On Behalf Of Dave Lowry
> > Sent: Thursday, July 16, 1998 5:32 PM
> > To: gmcmotorhome
> > Subject: GMC: CB Antenna
> >
> >
> > Craig,
> >
> > I recently had an antenna installed on my '76 Royale and chose a
> > "thru-the-glass" model. Being a former avid CB'er (lots of expensive
> > equipment), I was skeptical of its performance, but I didn't want
> > any extra
> > holes drilled in my just painted lady. I was pleasantly surprized. Good
> > range, low noise, and pulls in weather channels also.
> >
> > I had it mounted at the top rear corner of the passenger side glass, just
> > ahead of the awning support. I ordered mine from Camping World for about
> > $20, but it's probably available from other sources also.
> > Incidently, I had
> > their no-ground side mount antenna on my previous coach, and it
> > also worked
> > well.
> >
> > Hope this helps, Dave
> >
> >
> >
> Craig,
> My 74 Painted Desert has a pair of antennas
> mounted on the top of the mirror supports, One
> on each side..I dont know how the system works
> as I havent a CB. Maybe soon I'll check it out.
> My little brother ( Hes taller then Me ..HaHa )
> has been messing with CB radios for the last
> few years. Maybe he will check the thing out
> and i can give you more input on it. I havent
> done anything with CBs since the 70s.
> Rob Teed
