[aprssig] APRS (Fire) In A Car

Wes Johnston aprs at kd4rdb.com
Tue Jan 24 08:33:36 EST 2006

I had a mobile radio loose it's ground and when the TNC keyed up the
radio, the radio sought a ground back thru the TNC burning a ground
trace in the TNC PCB.... err is that a fuseable link?? lol!  This
suddely made me realize why it was suggested that we fuse BOTH leads.
I've also heard of the same thing happening to radios when the engine
block looses it's ground strap and you try to start your car.  Bob makes
a good point about the wire being big enough to carry enough current to
pop your fuse.

If you want to protect your radio from car starting, put a 20A fuse in
the neg lead of the radio.  Of course another solution is to run the
negative lead of the radio to the - battery terminal and don't ground
your rig to the car chassis.

If you want to protext your TNCs and GPSs from radios loosing ground,
put a 1A fuse in their negative leads.


Robert Bruninga wrote:
>>OK I get the small wire point but, what's the best solution?
>>Two separate fuses?
> Either two separate fuses, a smaller one appropriate
> for the smaller wire, or the one fuse (or pair of fuses)
> to the radio, but then big enough wire to the GPS
> so that any short -will- blow the 20 amp fuse and
> not burn the wire instead.  de Wb4APR
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