>-----Original Message-----
>From: Michael Heckrotte [mailto:[email protected]]
>Sent: Tuesday, December 18, 2001 10:32 AM
>To: Wan Juang Foo
>Cc: EMC-PSTC
>Subject: Re: Enclosed OATS facilities in snow country
>
>
>
>All the various standards specify that a metal ground plane be used for
>an OATS. This is to alleviate the problem with variations in the
>conductivity of the ground, due to water table variations at any one
>site or due to different soil and base materials among sites. If the
>level of the water table is affecting your site characteristics, this
>suggests that the metal ground plane is too small.
>
>Regarding snow accumulation on top of a metal ground plane, this will
>also affect the characteristics of the site. Measurements at any one
>particular turntable azimuth and antenna height will show great
>deviations around a null; scanning the antenna height removes
>this great
>uncertainty by measuring the peak.
>
>The real test of the effect of snow accumulation is to perform two NSA
>measurements, one in dry weather and one with the maximum snow
>coverage,
>then compare these results. The height at which the peak occurs may
>change (and indeed ought to correlate with the change in height of the
>reflecting plane due to snow, taking into account the conductivity and
>dielectric constant of the snow compared to the conductivity of the
>metal plane), but as long as the magnitude falls within the +/- 4 dB
>tolerance, the site is okay.
>
>Mike Heckrotte
Mike:
Another variable is that the moisture content of snow varies considerably.
You would want to do the snow measurement using relatively "wet" snow.
Regards,
Ed
Ed Price
[email protected]
Electromagnetic Compatibility Lab
Cubic Defense Systems
San Diego, CA USA
858-505-2780 (Voice)
858-505-1583 (Fax)
Military & Avionics EMC Services Is Our Specialty
Shake-Bake-Shock - Metrology - Reliability Analysis
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