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Re: [RFI] Help with broadcast interference

To: "Jim Brown" <jimbrown.enteract@rcn.com>,"RFI List" <rfi@contesting.com>
Subject: Re: [RFI] Help with broadcast interference
From: "Tom Rauch" <w8ji@contesting.com>
Reply-to: Tom Rauch <w8ji@contesting.com>
Date: Mon, 16 Feb 2004 05:52:41 -0500
List-post: <mailto:rfi@contesting.com>
Right here is the key:

> On Thu, 12 Feb 2004 22:01:56 -0500, William Liporace - NA2NA wrote:
> >At the tower (with in a foot)

You can do that. Anything the meter reads is USELESS because the tower
becomes the antenna, not the loop in the FSM.

It, in effect, makes the FSM have a pretty large reasonably efficient
antenna instead of a very small loop.

The same is true (but with very rapidly decreasing effect with distance)
within about 1 wl of any large metal structure. Mutual coupling between the
sense antenna and anything around it causes the meter to read incorrect
signal levels compared to what would be there without these unintentional

The only thing that matters is what he has inside the coax reaching the
radio, and even that can be misleading since levels are normally measured
with a 50 ohm broadband termination and the receiver almost always doesn't
look anything like 50 ohms.

It's really a complex issue to do absolute measurements, but at least a
terminated cable level comparison with a selective level meter or spectrum
analyzer would provide some useful starting point. A FSM is next to useless.

73 Tom

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