[Scan-DC] Antenna pattern for DCA @ 119.1 MHz?

[djoneses]

Andy:

Although I do not know the exact answer to your question, my thought has all
been that the 119.1 tower frequency transmitter is not located at DCA.  And
since the controllers have the ability to select transmitter sites, they may
choose a different transmitter site based on traffic direction.
Additionally there probably is some antenna uptilt. -- could be very minor
only a few degrees -- but combined with the antenna location, this results
in a weak signal

On the other hand, the helo transmitter site may be local to DCA and the
antenna may have a truer horizontal pattern since it only needs to serve
aircraft at relatively low altitudes (compared to approaching fixed wing
aircraft) and in the local area.

I often wondered if the 119.1 tower transmitter is not located at the FAA
Falls Church site.  Maybe a little foxhunting is in order.

David

-----Original Message-----
From: Scan-DC [mailto:scan-dc-bounces at mailman.qth.net] On Behalf Of Andrew
Clegg
Sent: Monday, December 08, 2014 9:57 AM
To: Scan-DC at mailman.qth.net
Subject: [Scan-DC] Antenna pattern for DCA @ 119.1 MHz?

I've noticed that the 119.1 MHz tower frequency from DCA is surprisingly
weak. I can barely hear the tower 4 miles away from a rooftop up 220 ft.
Even in the parking lot at Gravelly Point, the signal isn't exactly
gangbusters. The planes come in fine at both. On the other hand, the 134.35
MHz simulcast frequency that the tower uses to communicate with helicopters
comes in loud and clear 4 miles away, and the 257.6 MHz simulcast channel in
the milair band comes in reasonably well too.
Does someone on the list know if by chance the 119.1 MHz DCA antenna has a
significant electrical uptilt that keeps the pattern along the horizon very
low? That would seem odd, because even ~10 miles away, where the tower first
starts communicating with inbound planes, the planes are at a relatively low
elevation as seen from the airport. But I can't seem to figure out why 119.1
is so weak. Maybe the 119.1 antenna on the southeast side of the tower and
blocked to the west (where I am) and the north (where Gravelly Point is)?
That would seem odd too.
Any ideas? This has puzzled me for several years.
73,Andy
 		 	   		  
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