Allen,
We have a similar chamber with similar issues. We use the immunity chamber
as a precompliance emissions chamber also. It's a lot of work to remove the
tiles from the floor so we left them in place for precompliance emissions
investigations. We use a biconilog antenna for both emissions and immunity.
We have found that our "correlation factor" to our OATS is roughly +/- 8
dB. This works for us as the chamber eliminates the radio and TV ambients
and we can see the entire profile at a glance. We now do 90% of our
emissions mitigation in the chamber and then final compliance measurements
at the OATS.
Hope this insight helps.
Don Umbdenstock
Sensormatic
> ----------
> From: Tudor, Allen[SMTP:allen_tu...@pairgain.com]
> Reply To: Tudor, Allen
> 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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