World of Ham Radio 1997/WOHR97_AmSoft_(1997-02-01).iso/mods/misc_mod/mobile.doc

Internet Message Format | 1997-02-01 | 6KB

From philabs!prls!pyramid!decwrl!labrea!rutgers!ucsd!brian Fri Apr 21 13:22:27 EDT 1989
Article 11261 of rec.ham-radio:
Path: philabs!prls!pyramid!decwrl!labrea!rutgers!ucsd!brian
>From: [e-mail] (Brian Kantor)
Newsgroups: rec.ham-radio
Subject: Drilling Antenna Holes
Message-ID: <[e-mail]>
Date: 20 Apr 89 14:28:10 GMT
Organization: The Avant-Garde of the Now, Ltd.
Lines: 95

A long time ago, in my misspent youth, I worked as a commercial
two-way radio technician.  As the youngest employee, I got to do
most of the installations.  It was good experience; after a while
it got to the point where I could install a complete trunk-mount
mobile phone in under an hour.

The trick to good antenna performance in a car is to put it on a
good groundplane, as high and as central as possible - like in the
middle of the roof.  In Detroit iron, this is often easy to do,
but foreign cars (such as my RX-7) it's not so easy.

Scout out your car: is there a dome light fixture underneath a good
roof spot for the antenna?  If so, you've got it made: the manufacturer
has already run cable channels and you can drill into the roof
without having to fiddle with the headliner cloth.  Just remove
the dome light assembly, drill the hole, and fish the coax.  Should
take about 1/2 hour even if you've never done it before.  Drill UP
from INSIDE, first with a 1/8" drill, then with a 3/8".  If your
antenna needs a larger hole (like 5/8"), use a chassis punch,
antenna drill, or a tapered reamer.

To fish the cable, use a piece of #14 house wire or something like
that; it's stiff enough to shove down channels and doorposts, and
strong enough that you can use it to pull the coax back up.  Take
off all the decorative covers, kickplates, etc., and follow the
route the car manufacturer used to run his wiring.  There's almost
always enough space left to fish at least one piece of RG58 through
there.  If you're using foamcore cable, be sure it won't be pinched.
It's a good idea to bend the end of the fishwire over into a blunt
end if you're fishing past cloth that will tear.  Wrap a little
tape over the bent end so that it doesn't act like a hook and snag
on something.

If your car doesn't have a dome light in the center of the roof,
then check the headliner.  If it's stretched cloth that isn't glued
to the underside of the roof, then you're still ok.  Peel away the
moulding at the edge above the door, and carefully peel the headliner
cloth off the glue where it's stuck to the doorframe.  Fish the
coax from the radio location to the top of the door before you
finalize the antenna location, since some manufacturers don't leave
cable channels you can use.  Remember that you can always tuck the
cable behind the moulding or inside window gaskets if you have to.

To drill the roof in a car with a stretched headliner, first take
a couple of safety pins and hook them into the cloth below where
you're going to drill.  Hang some fishing weights or a small child
from them to pull the headliner away from the roof.  Prepare your
drill: stick a piece of aquarium tubing over the 1/8" bit and tape
it in place so that when the drill breaks through, only about 1/4"
can penetrate.  Do the same with the 3/8" (a piece of garden hose
works well here).  Find the center of the roof by snapping a chalk
line or running a piece of string from the center of the hood
(usually the interior rearview mirror is in the center) to the
center of the back window.  Put a coke bottle or the antenna in
place and walk around the car a couple of times until you are
convinced that it's in the middle and people won't laugh at you
later.  Centerpunch the hole and drill, first with the 1/8" then
the 3/8".  Again, enlarge the hole with a tapered reamer if you
need to.  Now, from the top of roof, push your fish wire down and
to the side where you left the coax hanging at the roofline, and
pull it back up through the hole and attach it to the mount.

If you have one of those mounts that comes with the coax already
soldered to it, you just use more fishwire, then pull the coax back
along the path the fishwire took.

To find electrical power for your radio, you can best get it from
one of the heavy wires on the back of the ignition or headlight
switch, or on the relay panel if your car is modern enough to use
them.  If your radio doesn't need continuous power, use the
"accessory" terminal so that you don't have to remember to turn it off
every time you get out of the car.  If you don't smoke, a real good
place is the wire to the cigarette lighter.  Find a good ground (like a
self-tapping screw and star lockwasher into the body sheetmetal).

Power amplifier wiring is high current stuff, and should probably
go to the battery or the starter motor terminal.  If you use the
battery connection, shoot it with a couple of coats of clear Krylon
paint after it's back together to minimize corrosion.

Almost every rice-rocket on the market needs an external speaker to
sound good.  Put it where it can sorta face the driver, but don't put it
where it's in the way, and DON'T put it on the doorpost where it will
slice up your face when you crash.

You probably aren't installing a trunkmount radio, so I don't need to
remind you not to drill into the top of the gas tank, do i?

Remember, for mounting radios, big self-tapping sheetmetal screws are
your friends.  Use lockwashers on EVERYTHING - it's hard to control a
car when a 15 pound radio just fell off the dashboard onto your right
foot on the freeway in the #1 lane at 75 MPH.

Have fun!
    - Brian