[BC] Re: Engineering Advice

[Mark Humphrey]

On Sat, Feb 14, 2009 at 8:55 PM, Mike McCarthy <Towers at mre.com> wrote:
>
> Bob Surrette told of this project at the Wisconsin clinic a couple years
> ago.  It was for a Class B FM station which was replacing a tower atop a
> hospital in a eastern NYC borough. This station has a specific limitation in
> it's lease that power density in any portion of the building interior could
> not be above a certain level. Yet they wanted to have good coverage on the
> ground around the hospital as it was in NYC and it was mixed residential and
> commercial.  The original antenna was installed long before RFI and RFR had
> become issues.
>
> They ended up using a very specific spacing and power ratio to each bay. I
> think it was an 8 bay with power ratio of .25 on the end bays, .5 on the
> next bays in, and 1 on the inner 4 bays.  Or was it 0.1, 0.4, 0.8 and 1.0.
>
> There is a specific math term applicable to this type of stepping which I
> can't recall.  Bob...please help me here.  I going on fuzzy memory.

It's probably a binomial feed.

Here's a copy of WFUV's DA proof showing this antenna's calculated
elevation pattern.  The relative field drops to  0.1 at 13 degrees
below the horizon, and remains less than 0.05 below 21 degrees.

http://fjallfoss.fcc.gov/prod/cdbs/forms/prod/getattachment_exh.cgi?exhibit_id=388478

Scott has some pictures of WFUV's antenna on his tower site website:

http://www.fybush.com/sites/2008/site-080328.html

Mark