I just remembered that there are these excerpts from
factory 2-way radio installations guidlines for Ford, GM,
and Crysler in the ARRL RFI Handbook. Here is a
summary of what they recommend:
"Transceiver power connections should be made
directly to the battery and appropriately fused as close
to the battery as possible. A weatherproof fuseholder is
recommended. Twist the negative power leads together
to enhance noise immunity."
"Connecting the radio power on General Motors
vehicles is model dependent. The installer must decide
which method is appropriate:
1) Connect the positive and negative leads to the directly
to the battery (ed. fuses in both leads are shown in the
2) Connect the positive lead to auxillary power........
and connect the negative lead directly to the negative
terminal of the battery.
3) Connect the positive lead to auxillary power terminal
and connect the negative lead to the battery body connection
point (identified by a short #10 AWG or larger wire running
from the negative battery terminal to the body of the vehicle).
4) Connect the positive and negative leads to the Special
Equipment option (SEO) wiring provided for this purpose. "
GM goes on:
"If connections are made directly to the battery
terminals.........blah blah.... Note: it is recommended that
a fuse be placed in the transceiver negative lead to prevent
possible transceiver damage in the event that the battery
to engine ground lead is inadvertently disconnected."
"The positive power connection should be made directly
to the battery as fused as close to the battery as possible.
The negative power connection should be made to the body
sheet metal adjacent to the negative battery connection.
This connection should not be fused."
Later on it also says:
"DO NOT FUSE THE GROUND LEAD. If the ground lead
fuse were to open, the entire supply current would be
conducted by the coax shield. This could cause the feedline
to overheat, with possible resulting damage.
Chrysler makes a good point here about fusing the
negative lead which hadn't occured to me. If that negative
lead fuse opens you could end up forcing all of your
supply return through the coax shield feeding the antenna,
and you wouldn't know it until the coax melted. Seems like
the best method would be to run the radio's power return
wire to the chassis metal right next to the battery or to the
negative battery terminal to chassis connection point
(same general area) and connect the radio's power
return wire to that point without a fuse.
73 de Mike, W4EF......................................
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
TowerTalk mailing list