[BC] RFI stalls cars near Empire State Building

[Bob Tarsio]

Robert:

It is difficult to predict with calculated data what the actual field
intensity at street level will be. We are talking about one of the most
diverse reflective and absorptive environments known to RF transmission.
With high fields from reflections it is quite possible that the field
intensities are much less than predicted for smooth earth at street level.
This is a real problem in and around Manhattan particularly for that CBS DTV
antenna due its poor circularity. Side mounting on that tower was a poor
alternative to top mounting which was not possible at the time CBS did that
project. The tower was reinforced a couple of years ago to support the
present configuration but with the 1950 era Stainless tower it was not
possible to support the original proposal for a top mounted panel antenna
affectionately known at the time as MOAPA or mother of all panel antennas.

Just so you don't think I am making off hand comments about Empire I wrote
the specifications for all three of the FM antennas and combiner systems
presently in use at Empire. I was project manager for the VHF combiner and
the larger of the two ERI FM combiners systems projects in use there too. I
have made extensive RF safety measurements in and around the building being
retained by Helmsley Spear, CBS, ABC, Skyline Tower Service, ERI, and Con
Edison. I also worked as a field engineer for Silliman & Silliman during the
early RFR measurements that were made in the building as far back as 1987. I
am routinely retained as the RF safety engineer of record for any
maintenance performed on the outside of the building requiring station
shutdowns. I can tell you this from my experience up there, predicted field
intensities invariably differ from measured results usually on the low side
but not always. Re radiation absorption and antenna performance all play a
role in this phenomenon. Every antenna project since the mid 1980s has
always worked toward the goal of reducing downward radiation when possible.
The exception was the new mini master FM antenna which is a single bay
antenna. But even this antenna did reduce somewhat the total downward
contribution in that it replaced three separate single bay antennas. Two of
those antennas one an RCA and the other an MCI panel were located lower on
the tower. The elimination of those antennas offered slightly less FM RF in
the downward direction by virtue of the fact that all three FM stations
previously using separate antennas are now utilizing the same single bay
antenna at a greater distance from where people are in and around the
observatories.

I am not saying that there aren't higher than usually expected field
strengths around Empire. I only take issue for using predicted data for
anything other than an academic exercise.

Bob Tarsio
www.Broadcast-Devices.com

Tel. (914) 737-5032
Fax (914) 736-6916



-----Original Message-----
From: R A Meuser
Sent: Monday, January 28, 2008 17:32


The DTV master antenna's most significant side lobe is about - 6 db at
45 to about 55 degrees or approx 2000 feet out. Other side lobes that
would impact the area where cars are having problems are about -10 db.
The main lobe is has .75 degree beam tilt and a gain of 12 to 19 db,
depending on the channel. The RSS voltage for 11 significant UHF
stations on Empire is approximately between 2 and 7 volts on the ground
for around 2000 feet distance. This does not include the contribution of
VHF TV stations which in general have much lower gain antennas nor does
it include about 3 volts RSS for all the FM stations combined. Could
there be nearly 10 volts RSS for all stations? - very possibly