> >Inside the radio, the negative leads of any HF radio and
> >almost all VHF/UHF amateur radios are virtually always
> >connected together via the chassis or PC board grounds.
>
> You're thinking resistance, not inductance or loop area.
Why does that matter?
When you
> get the power via the closely paired cable (even better if
it's
> twisted), you minimize the loop area of any issues with RF
on that
> power connection.
That's not worth even considering Jim. The issue is NOT
differential mode RF on the power cables. That are always
very well bypassed together, and PA's of any substatial
power level are push pull anyway. That further suppresses
any tiny amount of differential mode RF on power cables that
might exist.
Virtually all RF problems are common mode, and anything you
do to increase path impedance helps. That's another
(although mostly moot) reason to NOT tie ground to the
battery.
If you use only the body of the car for the
> return, you get a low resistance (and low inductance) for
that half
> of the dc path, but there's a big loop area between the
positive
> lead and the car body, and any trash on the power will
then radiate.
Time to buy a new brand of radio or repair the old one if
that is an issue! I've never seen a radio like that. And if
I did, I'd fix it with a bypass cap, a few beads, or a combo
on the positve lead.
> AND that big loop will act as a receiving antenna,
coupling RF onto
> the power line. That could be a problem if the
microprocessors are
> using the power system to communicate, which I am told
some do.
Simply running the negative lead of a radio that is already
bonded to the chassis that is already bonded to the car via
other paths can't possibly make an improvement in the big
scheme of things Jim. It aggravates the DC loop issues, and
if you had common mode on the radio chassis having a long
ground lead to a battery terminal can't possibly help
anything.
I've worked with RF grounds all my working life. The battery
terminal is NOT a good RF ground point, and the RF loop
would not be between the positive and negative power leads
anyway. It would (if it was an issue) almost certainly be
common mode problems caused by a poor antenna ground
allowing the radio chassis to "pump" up and down with a
portion of the antenna current. Running a parallel wire
would aggravate RF current flowing into things connected to
the battery positive terminal, not reduce it.
73 Tom
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