[aprssig] RE: D700 Honda Odyssey Mounting Options

Marsh James w9nje at sbcglobal.net
Tue Nov 15 09:51:45 CST 2005

Hi Dave; 
Do you return all your electronic grounds to a common ground point? It's important in test and monitoring equipment; but, I was wondering about autos?

Dave Baxter <dave at emv.co.uk> wrote:
Take care Brad.

If you ground the rig to the vehicle frame, you shouldn't really use the
fuse in the radio ground lead. It's only needed in that lead if it goes
direct to the battery -ve, as there is a less than rare chance that the
car's own battery ground can become intermittent in time, so engine
cranking current can pass through your radio to ground, with, err,
smokey and expensive results.

If you ground the radio direct to the frame, a fuse there if that blew,
will then cause the radio's own power current to pass down the coax
outer, or other accessory grounds that may not be able to take that
current, especially on high power TX.

If you sketch out a typical auto electrical setup (just the basics,
battery, starter, gen', but including the grounds) showing the exact way
things are all joined together, including your radio, then "cut" the
battery ground lead, and work out where the big currents go, you'll see
what could happen.

If you think it doesn't, beware, it's quite common for vehicle ground
leads to go "High Resistance" but remain mechanically sound. I've seen
enough over the years, and had one electrical fire when driving due to
"interesting" British fusing philosophy, that I'd not want to hear of
anything like that happening again.

(Most auto electrical problems are related in one way or another to bad
grounding somewhere, but it takes skill and understanding to diagnose

To make sure this doesn't happen, I have two grounds between the engine
and the frame. One ground from the battery to the frame, and one
between the battery and the engine! No odd electrical noises on TX or
RX, the battery always charges well, and it turns the lump over
extremely well on a cold frosty morning, and next to no chance of any
damage to accessories like radios etc...

All my RF kit, has it's own ground to the frame, independent of the
engine or battery, so they only need fuses in the + leads.

Stay safe..

Dave G0WBX.

> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org 
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Brad [VE3BSM]
> Sent: Tuesday, November 15, 2005 12:41 PM
> To: 'TAPR APRS Mailing List'
> Subject: RE: [aprssig] RE: D700 Honda Odyssey Mounting Options
> >>
> If you run a seperate power cable for the rig, including the 
> -ve lead direct to the battery, remember to fuse the -ve wire 
> too, or a loose battery ground strap (it does happen) can 
> become very expensive when you next try to start the engine!..
> <<
> I'm not going to run a separate -ve lead. I'm aware it'd be 
> better to do so but I barely fit the +ve lead through the 
> available grommet. I'll just ground to the frame. I am, 
> however, going to fuse the -ve lead this time.
> Brad.

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Jim. w9nje at sbcglobal.net 

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