----- Original Message -----
From: "David Jordan" <wa3gin@erols.com>
> Thanks for the fast response Tom. I always appreciate a thread where
> you're engaged in the conversation. I've spoken to Ford and Chrysler
> EMI engineers and they all believe this myth, as you say!
>
If you look at the ARRL RFI Handbook, it excerpts 2-way radio
install recommendations from the big 3 automakers. They all
suggest running a negative lead back to the battery, but they
disagree about how to terminate the lead. One suggests
connecting it to the battery with a fuse, while another suggests
that this is a bad idea because if the fuse blows the radio DC
return current will be forced through the antenna coax braid.
Instead they suggest connecting the negative lead to the battery
to chassis connection point that sits adjacent to the battery.
Here are the excerpts:
FORD:
"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."
GM:
"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
diagram) .
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."
CHRYSLER:
"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.
My negative lead goes to the battery with a fuse, but I
haven't done any testing to see what configuration produces
the best results. It's on the list (the very long list).
73 de Mike, W4EF.................................................
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