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

Mon Dec 8 12:03:06 EST 2014

Geez, I used to earn my living as a nationwide trouble shooter for this 
stuff. My desk was at 800 Indep Ave (FAA HQ). You have aroused the 
engineer instinct in me.
Does anyone have a signal level to report?
Locations? Andy have you tried Daingerfield Island (Sailing Marina)?
Have you tried monitoring Clearance Delivery and Ground Control?
Both have service volumes to encompass the entire airport proper
Ground control and tower freq's can be combined as traffic volume allows 
i.e. Tower controller simulcasts on one or the other at quiet times.
I am trying to remember about audio compression which evened out 
differences in controller's audio/head set characteristics.
But that is set to a well defined protocol and there is no free lancing, 
especially at a high visibility terminal such as DCA
It is possible for tower ERP and frequency coordination issues the power 
on that freq has been reduced (what sig level do you show compared to 
other freq's?)
Can you hear IAD?
Each freq has a backup TX/RX and antenna. They are checked daily and at 
some facilities alternated for the entire day
They used to have BUEC (Backup Emerg Comm) which had it's own antenna 
and battery supply in case the entire airport went dark
It had limited range and was (hopefully) seldom used.
I hear BWI tower as well as airplanes on the ground with no difference 
in audio quality
Exciting stuff (to me anyway)
73, Bob

On 12/8/2014 11:22 AM, Scott, KB3JQQ via Scan-DC wrote:
> I can't hear the 119.0 from BWI very
> far from the airport, either. Theymight be designed that way. ==
> Have scanners, do listen.
>
>
>        From: djoneses <djoneses at verizon.net>
>
> 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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