[Antennas] Log Periodic

2002年5月24日 11:56:33 -0700

I agree with the question what is a ground?
A few years ago I was the new one on a team for building a process control 
computer. Most of the basic work was done so I did what I was told. It 
was a very basic system as compared to todays things, probably one of the 
first in a large refining plant. It consisted mainly of sensors and 
controlers, ie sense the level in a tank, control the valve to either fill 
it or empty the tank. The plants had many electrical devices running many 
many amps and volts. The grounds were so bad that some of the workersat 
times, would feel tingling sensations when showering. The different 
grounding points had a Potential difference between them, hence a voltage 
and an amperage. The best solution was to have a ground line or extra wire 
(heavy) between all points and ground all to this bus for all sensors and 
controller and the computer. I think for this reason there is in some 
literature the use of grounding and earthing. The ground line no longer 
represents tying to the earth, whilst earthing does.
Just a comment from my observations of many years ago.
Chris opr VE7HCB
At 12:48 PM 2002年05月24日 -0400, A10382 wrote:
>This seems like one of the best reasons not to 'ground' (as in earth ground)
>the 'return' coax shield or the non-driven side of the dipole at the
>antenna. There's a significant amount of conducting material between the
>shack ground and the antenna feed points.
>>I believe this has the potential of creating a classic ground loop where
>there would be current flowing over the shield due to different potentials
>at the ground points. Even a very small difference in ground potentials,
>when connected through a low resistance path, will create a lot of
>current...
>>I've only actually seen twice.. once in cabling computing devices between
>buildings (computer in one building and the data collection device across
>the parking lot). The shield on the data cable was carrying almost three
>amps at about a half a volt.
>>A second, back when I was still an un-ionized atom, and more severe
>experience was the potential between the ships keel and a shop 40 feet
>higher was almost 2 volts and the coax shield was carrying about 4 amps... a
>very 'shocking' experience for the gear.
>>73
>Frank
>> ._._.
>----- Original Message -----
>From: "Cletus W Whitaker" <[email protected]>
>To: <[email protected]>; <[email protected]>
>Sent: Friday, May 24, 2002 5:24 AM
>Subject: Re:[Antennas] Log Periodic
>>> > de WB2CPN South Central Pennsylvania 2002年05月24日
> >
> > As you say, the two parts of the boom are insulated from the mast, so they
> > are "ungrounded", and the coax shield connects to one of the boom
>sections,
> > so the coax is not "grounded", or at least not there. BUT, the bead balun
> > is between the boom and the coax that goes down to your shack. Among
>other
> > things, the bead balun is the demarcation between what can be "grounded"
> > and what can not be "grounded". You may "ground" the coax cable, (there
>are
> > a few reasons why I don't recommend this), anywhere between your shack and
> > the bead balun. Just don't do it BETWEEN the bead balun and the antenna
>boom.
> > Sometimes bead baluns can be avoided by running the coax up through the
> > inside of one of the booms and connecting it at the far end. When I say
> > "ground", above, I mean a large piece of metal nearby. Such as the mast.
> > I don't mean the stuff they grow flowers in, that's what you "ground" the
> > things in your shack to. 73 Clete
> > - - -
> >
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