On Fri, 10 Oct 1997 09:41:29 +0000 w8jitom@postoffice.worldnet.att.net
writes:
>> From: Frank Donovan <donovanf@sgate.com>
>
>Frank's post was excellent, and a very accurate description of a
>problem commonly occurring with ANY receiving antenna...not just
>Beverages.
>
>Why install a low noise antenna far away from the noisy house wiring,
>just to run a transmission line out to the antenna with no isolation
>for the outside of the shield? The noise and unwanted signals can
>zip right along the shield to the receiving antenna, essentially "turn
>
>the corner", and come right on in!
>
>> My installation uses two ground rods, one at the cold end of the
>Beverage
>> feedpoint 9:1 transformer and a second ground rod connected to the
>> feedline shield at the feedline-side of the ferrite bead choke.
>
>I'd like to add something else I do, that Frank mentioned earlier.
>
>I use a completely isolated primary on the transformer if possible.
>That removes the direct connection between the antenna system and the
>feedline shield. I ground the feedline through a separate ground rod
>several feet from the antenna, using a CATV grounding block.
That was the answer I was looking for Tom. I build my 9:1 xfmrs with
seperate ground leads but never had a BC band problem at the old QTH so I
just tied them to a common ground.
Another question.... I have 4 Beverages coming to one tree. I run a
short length of coax from each transformer to the RCS-4 remote switch.
Each Beverage has its own ground rod and they are not directly connected
to each other in the ground. Spacing of the rods is about 4' from each
other.
How would you guys suggest re-configuring this? Since the RCS-4 is a
common point for all cables, doesnt this contribute to all sort of ground
loop problems? I do not want to run individual 700' feedlines back to
the house!
Tnx Carl KM1H
>
>Between that grounding block and the cable from the shack, I use
>beads.
>
>By the way, a Faraday shield does not reduce common mode coupling
>between the shield and the antenna system when using small
>transformers with small windings. (If you are using six inch
>diameter air wound coils like they used in the 30's it might help,
>however.) As a matter of fact, it actually INCREASES unwanted common
>mode ground system coupling in many systems. For a Faraday shield
>to be effective in this application, it needs to connect to its own
>separate ground system that is not common to either the feedline OR
>antenna.
>
>73, Tom W8JI
> -
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