Allen,

I would like to clarify one point.  I use a biconilog in the chamber.  All
chamber work is "rough" or ballpark.

I use a biconical and a log periodic on the OATS.  

There are a few articles around that identify repeatability issues with a
biconilog.  However, for pre-compliance biconilog is adequate as long as you
know the antenna's and chamber's limitations.

Don  


> ----------
> From:
> umbdenst...@sensormatic.com[SMTP:umbdenst...@sensormatic.com]
> Reply To:     umbdenst...@sensormatic.com
> Sent:         Wednesday, November 15, 2000 12:08 PM
> To:   emc-p...@ieee.org; allen_tu...@pairgain.com
> Subject:      RE: Which Antenna?
> 
> 
> 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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> 
> -------------------------------------------
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> 

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