[SI-LIST] Re: loop antenna (mis)behavior

How are you measuring your phase?  What is your reference?  Are you =
using a
scope or ?  Are you sure that the "loop" is the antenna or is something =
else
acting as the real antenna?

Tom Dagostino
Teraspeed(R) Labs
13610 SW Harness Lane
Beaverton, OR 97008
503-430-1065
503-430-1285 FAX
tom@xxxxxxxxxxxxx
www.teraspeed.com

Teraspeed Consulting Group LLC
121 North River Drive
Narragansett, RI 02882
401-284-1827=20


-----Original Message-----
From: si-list-bounce@xxxxxxxxxxxxx [mailto:si-list-bounce@xxxxxxxxxxxxx] =
On
Behalf Of Gene theBean
Sent: Wednesday, May 28, 2008 2:53 PM
To: si-list@xxxxxxxxxxxxx
Subject: [SI-LIST] loop antenna (mis)behavior

I need some help from anyone who knows about fields and/or rf =
propagation.
=A0Here's my issue:
I have a system with a transmitter sending a continuous 2 MHz signal out
using a loop antenna. =A0The loop is electrically small, maybe 5" in =
diameter
and around 7 turns. =A0The receiving antennae (there's 2 of=A0them) are =
likewise
the same size and number of loops, and is around a couple of feet away =
from
the transmitter. =A0The RX antennae are just a couple of inches away =
from each
other. =A0They all share a common centerline. Also, the antenna =
positions are
fixed on a common, non-magnetic, core.

Here's the problem: there is absolutely no phase change in either RX
antenna. =A0That is, they are at 0 degrees phase, relative to one =
another.
Changing polarity on either RX antenna does not affect the relative =
phase,
where the expected phase shift would then be 180 degrees.

In an experiment, using duplicate RX antenna sections, we discovered =
that
the very near field behavior is quite different than the far. =A0And, =
this
'near' behavior only is true withing an inch or 2 of the transmitters.
=A0There, the RX phase can changed by swapping=A0the polarity of =
the=A0antenna
leads.=A0=A0Fine.=A0=A0Moving=A0these 'floating' sections in the =
vicinity of the
TX=A0reveals phase inversions depending upon=A0the position. =A0But, =
again, moving
away from=A0this near field=A0area,=A0the=A0phasing is=A0always zero
degrees=A0regardless of the=A0antenna polarity.
=20
Anyone know what may be going on?



     =20
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