[BC] Engineering Advice

[Mike McCarthy]

Here is a really good example.

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.

But it achieved the desired results and multipath was actually very good in 
and around Manhattan.

While this is an extreme example...it shows doing it by known math and then 
following with proper implementation can achieve desired (goal) results.

MM

At 10:38 AM 2/14/2009 -0600, Dave Dunsmoor wrote

> > Until a few years ago, I didn't realize that one could define the FM bay
> > spacing to anything desired without a special CP to achieve very specific
> > vertical pattern results. Not just 1/2 and full.  The conditions and
> > results can and will vary by location, terrain, and a host of other
>factors
> > which are generally unique to a site. So spacing is a factor to be
>considered.
>
>Hmmm, good point. One that I've not had to consider before just now either.
>But it is identical to how the vertical guidance portion of the ILS is setup
>upon
>commissioning. If we were transmitting over a perfectly flat sheet of
>copper,
>the spacing above ground level would be ~ 14 and 28'. But it's NEVER that.
>
>It's defined by lobe maximum and null, and determined by the location in
>space by elaborately equipped aircraft, and we adjust the antenna spacing
>(and several other parameters) to achieve exactly this.
>
>Good insight, thanks.
>
>Dave Dunsmoor