ANother question on antenna

Archived from groups: rec.audio.car,rec.audio.tech (More info?)

I bought a car antenna which requires the base to be grounded to
the car's body. I wanted to know what would happen if I would
connect the antenna ground all the way back to the battery
ground, not the car's body. Would this cause bad radio reception?
I am wondering because it is currently grounded next to the
antenna hole on the fender, and I am getting some static in FM
reception at location in the city where I do not with other cars.

TIA

Archived from groups: rec.audio.car,rec.audio.tech (More info?)

"Frank" <NOSPAM@NOSPAM.com> wrote in message
news:C8idnTUbk_IHIK3eRVn-tw@rogers.com

> I bought a car antenna which requires the base to be
> grounded to the car's body.

That's probably done so that the car body can be part of the
ground plane for the antenna.

> I wanted to know what would
> happen if I would connect the antenna ground all the way
> back to the battery ground, not the car's body.

It would probabaly decrease the signal strength from the
antenna.

> Would this cause bad radio reception?

Depends on the circumstances. At long distances from the
transmitter, undoing the intended ground plane could hurt.

>I am wondering because it
> is currently grounded next to the antenna hole on the
> fender, and I am getting some static in FM reception at
> location in the city where I do not with other cars.

FM reception in cities is prone to that. This effect is
dependent on the directivity of your antenna. The
directivity of most car antennas is partially dependent on
the shape of the sheet metal around them. Is this antenna
mounted in an atypical spot on your vehicle?

Archived from groups: rec.audio.car,rec.audio.tech (More info?)

"GregS" <szekeres@pitt.edu> wrote in message
newsgrm0e$kpl$1@usenet01.srv.cis.pitt.edu...
> In article <C8idnTUbk_IHIK3eRVn-tw@rogers.com>, "Frank"
> <NOSPAM@NOSPAM.com> wrote:
>>I bought a car antenna which requires the base to be grounded
>>to
>>the car's body. I wanted to know what would happen if I would
>>connect the antenna ground all the way back to the battery
>>ground, not the car's body. Would this cause bad radio
>>reception?
>>I am wondering because it is currently grounded next to the
>>antenna hole on the fender, and I am getting some static in FM
>>reception at location in the city where I do not with other
>>cars.
>>
>>TIA
>>
>>
>
> It is a ground loop, but you have to use it. Well you don't
> really.
> Try it and see how things work!
>
> greg

What is a "ground loop"? Can you explain what is does? Thanks!

Archived from groups: rec.audio.car,rec.audio.tech (More info?)

On Wed, 21 Sep 2005 19:13:12 -0400, "Frank" <NOSPAM@NOSPAM.com> wrote:

>
>"GregS" <szekeres@pitt.edu> wrote in message
>newsgrm0e$kpl$1@usenet01.srv.cis.pitt.edu...
>> In article <C8idnTUbk_IHIK3eRVn-tw@rogers.com>, "Frank"
>> <NOSPAM@NOSPAM.com> wrote:
>>>I bought a car antenna which requires the base to be grounded
>>>to
>>>the car's body. I wanted to know what would happen if I would
>>>connect the antenna ground all the way back to the battery
>>>ground, not the car's body. Would this cause bad radio
>>>reception?
>>>I am wondering because it is currently grounded next to the
>>>antenna hole on the fender, and I am getting some static in FM
>>>reception at location in the city where I do not with other
>>>cars.
>>>
>>>TIA
>>>
>>>
>>
>> It is a ground loop, but you have to use it. Well you don't
>> really.
>> Try it and see how things work!
>>
>> greg
>
>What is a "ground loop"? Can you explain what is does? Thanks!
>

A "ground loop" is a term used when not all components are grounded to
the same "reference voltage". We usually refer to ground as being at
zero volts.

As an example, let's say you have a car where the head unit is
grounded under the dash, the antenna is grounded at the fender, the
amplifier is grounded to a bolt in the trunk, and the engine block is
grounded via a grounding strap connected between the engine block and
the car's chassis. The negative terminal of the battery is connected
to the car's chassis as well.

In a perfect world this wouldn't be a problem, because every component
has a path to ground:

Sparkplugs and alternator - through the engine block to ground strap
to the chassis, then from the chassis to the battery via the other
ground strap.

Antenna - fender to battery via chassis strap

Head unit - ground wire in harness to chassis to battery via chassis
strap

Amplifier - From the bolt in the trunk, through the chassis, through
the chassis ground strap to the battery.

In reality, you can run into cases where not all of those "grounds"
are at the same voltage, because of poor/loose/missing connections or
corrosion. For instance, if the ground strap between the engine and
the chassis is missing, the engine components may still be grounded
through the engine mounts, but the connection might not be as good.

These small voltage differences cause stray currents in the ground
wires, and cause your components to pick up radiated noise from things
like the ignition, alternator, turn signal flashers, air conditioning
blower, and windshield wipers.

Ground loops are tricky, because some installations may work fine with
a different grounding location for every component, while others can
pick up radiated noise from something as simple as an extra ground
path between the chassis of the head unit and a metal bracket behind
the dash.

To minimize the possibility of ground loops, I usually run one
heavy-gauge ground wire from the battery back to a distribution block
in the trunk, and *all* of my amplifiers, equalizers, signal
processors, and the head unit get grounded to that one distribution
block. I leave the antenna ground alone, for the reason that the
other posters have mentioned. I also upgrade the battery-to-chassis
and engine-to-chassis ground straps using the same heavy wire that I
used between the battery and the distribution block.

Also, don't mount audio components directly to the metal chassis of
the car. Instead, mount them to a board, and then bolt the board to
the chassis. This will prevent the component from having two ground
paths (one through the ground wire and another through the chassis of
the component).

This may seem like overkill, but the first time you spend hours
tracking down radiated engine noise in your stereo, a single-point
grounding scheme like the one I described starts looking pretty
attractive.

Scott Gardner




--
Scott Gardner

"Clothes make the man. Naked people have little or no influence on society." --Mark Twain

Archived from groups: rec.audio.car,rec.audio.tech (More info?)

"Laurence Payne" wrote...
> "Frank" wrote:
>>I bought a car antenna which requires the base to be grounded to
>>the car's body. I wanted to know what would happen if I would
>>connect the antenna ground all the way back to the battery
>>ground, not the car's body. Would this cause bad radio reception?
>>I am wondering because it is currently grounded next to the
>>antenna hole on the fender, and I am getting some static in FM
>>reception at location in the city where I do not with other cars.
>
> We can spout theory at you. Or you can try. Car electrics are a
> Black Art. Let us know your result?

Car "electrics" are one thing. This is a VHF-RF question. Long
ground runs are not a good idea. Neither of these newsgroups is
really likely to get you a good answer. Suggest trying a newsgroup
where VHF antennas are discussed. (Perhaps one of the ham
newsgroups.)

Archived from groups: rec.audio.car,rec.audio.tech (More info?)

"GregS" <szekeres@pitt.edu> wrote in message
newsgrm0e$kpl$1@usenet01.srv.cis.pitt.edu...
> In article <C8idnTUbk_IHIK3eRVn-tw@rogers.com>, "Frank"
> <NOSPAM@NOSPAM.com> wrote:
>>I bought a car antenna which requires the base to be grounded to
>>the car's body. I wanted to know what would happen if I would
>>connect the antenna ground all the way back to the battery
>>ground, not the car's body. Would this cause bad radio reception?
>>I am wondering because it is currently grounded next to the
>>antenna hole on the fender, and I am getting some static in FM
>>reception at location in the city where I do not with other cars.
>>
>>TIA
>>
>>
>
> It is a ground loop, but you have to use it. Well you don't really.
> Try it and see how things work!
>
> greg

That's not a ground loop. There is no loop. There's no circuit to allow a
loop in an antenna.