[Amps] Powering 400w mobile amplifier...

[Bill Turner]

On Mon, 28 Jul 2003 23:14:14 -0400, "jeff millar"
<wa1hco at adelphia.net> wrote:

>Gerry...
>
>Definitely run two wires to the battery.  Also ground the Amp solidly to the
>car frame at it's mount point.  Also fuse _both_ power wires near the
>battery.  Several scenarios to worry about.
>    1. Battery ground to frame loses connection and you go to start it...all
>starter motor current goes through Amp ground lead
>    2. Amp ground lead opens, all amp current goes through coax to antenna
>ground

_________________________________________________________

With all due respect, Mr. Millar has given some bad advice here.

First off, there is no need to ground the amp chassis to the car
chassis.  In fact, doing so invites exactly the scenario in #1 above.
The amp needs the two wires to the battery, but that's all.  If you
feel the need to "ground" the amp chassis for RF, do it with a small
disc ceramic capacitor, .01 uF or so.  Make no DC connection.
However, you will find it works fine with no chassis ground connection
at all, either DC or RF.  If the chassis proves to be "hot" for RF,
you have an antenna problem, just like at home.  Fix it the same way.

Secondly, if you are concerned about scenario #1, do not directly
ground the coax at the antenna or any where else.  Any ground you need
should be done with a small capacitor as mentioned above.  This
includes the transceiver as well.  NO DC GROUNDS ANYWHERE EXCEPT AT
THE BATTERY.  If you follow this advice, neither scenario #1 or #2 can
happen.

Some antennas are internally grounded.  In those cases, break the coax
shield and install the .01 uF capacitor to jump the break.  Mag-mount
antennas are not normally grounded, but measure them to be sure.

I have seen pictures of radio equipment which has suffered the fate
mentioned in scenario #1 and it is not a pretty sight.  The radio will
be essentially destroyed.  A couple of cheap capacitors will prevent
it completely.

-- 
73, Bill W7TI