For emissions testing, the antenna should have a well balanced design when
used over a ground plane. Perhaps the antenna you are considering is not
well balanced. The balance issue shows up in the vertical orientation when
there is coupling to the ground plane and is not unusual in some bicons. I
am assuming that you will install a removable ground plan for FCC and ETSI
emissions measurements. 

Richard Woods

----------
From:  Tudor, Allen [SMTP:allen_tu...@pairgain.com]
Sent:  Wednesday, November 15, 2000 11:36 AM
To:  emc-p...@ieee.org
Subject:  Which Antenna?


Greetings,

I am having a fully anechoic pre-compliance test chamber built.  By fully
anechoic, I mean ferrite tiles will be installed on the floor as well as the
walls and ceiling.  The inner dimensions of the chamber will be 24 feet long
by 14 feet wide by 13 feet high.  The chamber will be used for radiated
emissions as well as radiated immunity.  Radiated emissions testing will be
from 30MHz to 1GHz.

I am looking at a biconilog antenna that can be used for emissions and
immunity testing.  However; for emissions measurements, the salesman
recommends that I use separate biconical and log-periodic antennas.  He says
that if I use the biconilog antenna for emissions measurements, there will
be some coupling to the ground plane when the antenna is in the vertical
position.  However, this chamber will have ferrite on the floor, so I don't
know if that is a valid argument.

Aside from the expense of two additional antennas, I have two conflicting
concerns.
1. I would rather not have to work with more than one antenna if I don't
have to due to down time and possible damage to an antenna.
2. On the flip side, I want to make sure that I have repeatable results,
especially at the low end of the spectrum.

Any advice would be greatly appreciated.

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