[TowerTalk] Station Ground

[Michael Tope]

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:

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. 

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......................................