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Re: LF: RE: RE: Re: RX-LOOP

To: [email protected]
Subject: Re: LF: RE: RE: Re: RX-LOOP
From: "Jay Rusgrove" <[email protected]>
Date: Mon, 28 Apr 2003 06:35:02 -0400
References: <2D280BB697C7EE4C979C5C89925418EFB05C1F@TNS-FBU-2E-003.corp.telenor.no>
Reply-to: [email protected]
Sender: <[email protected]>
Jan-Martin

Have you found that it makes any difference where the core is placed along the 
transmission line?

Jay Rusgrove, W1VD

[email protected] wrote:

Right,

but you may also use a balun. See RSGB book about EMC (or TVI ...suppose mine 
is quite old..) and wind the coax cable 10 or more turns through a ferrite core 
with sufficiently high permeability.

I use it for my active antenna, and it is of course mounted some distance above 
the roof. Since you don't need RG8/U type cable for LF it shouldn't be a 
problem to manage 10-20 turns through the toroid (provided you haven't 
installed the BNC connectors in the ends)

73, Jan-Martin, LA8AK

http://home.online.no/~la8ak/

-----Original Message-----
From: Ashlock,William [mailto:[email protected]]

Alan, all:

>I suspect that you need to isolate the loop feed with a small transformer.
It is possible that
>the feed from the loop is acting as a wire aerial and is conducting TV RFI
and noises from the
>house *back to the loop*.

Surprising how few understand the concept of the RFI actually going from the
receiver back to the antenna site. This applies to E-probe antennas as well.
The typical house/apartment is a mad jumble of LF RFI having both E and H
field components. The proper RF return for remote LF antennas is the ground
immediately under the antenna - not the safety (green wire) ground in the
shack that connects to the chassis of the receiver. The isolation
transformer installed in the coax lead-in offers the only way to sever these
totally different grounds. In severe cases one is needed both at the
receiver and at the antenna since a floating coax shield can pick up noise
before it leaves the vicinity of the shack.

BTW, an isolation transformed can be as simple as two 15-turn windings of
#22 to #28 wire on a common 3/4"dia X 1" ferrite RFI bead found on computer
power cords, monitor cables, communications cables, etc.

Bill A

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