Eric et al:
That same LPDA antenna was spec'ed by VOA for installation at their
proposed relay site in the Negev Desert in Israel in the late 80s. (I was
working for the consulting firm that had the contract to design it and W3ASK
was part of the team.) The whole site was intended to receive VOA audio via
satcom from CONUS for eventual relay into southcentral Asia due to Soviet
jamming of our CONUS-originated programming. The LPDA was intended as a
backup for the satcom link. As I recall the boom looked like it was made of
Rohn 45, or something of similar size.
The facility was never constructed because Gorby decided to initiate
his policy of glasnost and turned off the jammers. Sigh.
73 de
Gene Smar AD3F
P.S. The size of the reflector screen for the electronically steerable (!)
HF broadcast antennas at that site was measured in acres!
----- Original Message -----
From: "Eric Scace K3NA" <eric@k3na.org>
To: "steve d" <kc8qvo@yahoo.com>
Cc: <towertalk@contesting.com>
Sent: Thursday, October 25, 2007 8:01 PM
Subject: Re: [TowerTalk] Name this antenna
> That is the Leesburg FAA control center. I believe that it is a back-up
> HF facility to talk with FEMA HF facilities, other control centers, and
> possibly for aeronautical HF communications as well. Those antennas
> went in around 1980 or so.
>
> The antenna is a HyGain rotatable log periodic that covers 4-30 MHz. It
> is a design that has been sold to customers for over 30 years. The
> vertical pipe between the two facing towers is both the transmission
> line and the drive pipe for rotating the antenna. The rotator is at the
> base of the tower. The antenna can spin anywhere with no stops; a
> rotary joint connects the coax coming out of the ground to the tube
> going up in the air. That tube has to be kept pressurized with dry air
> or nitrogen to keep moisture out of it.
>
> I happened to get to use one of those antennas for a number of DX
> contests in the late 1970s. The one I used was installed on top of the
> National Weather Service headquarters building on the border between
> Silver Spring MD and Washington DC. That was a 17-story building on a
> ridge top, so the antenna was way up there. I was completely new to DX
> contesting, but there was a Collins HF station on the top floor with a
> kilowatt amp, so I gave it a spin for a year or two (lacking any station
> of my own). It worked pretty well on 80m! But, as impressive as it
> looks, it's basically equivalent to a 3-el Yagi on any one frequency.
>
> Eventually the Weather Service scrapped the antenna. The asymmetric
> wind loading (boom sticks out a lot more in the front than to the rear)
> put a lot of torque on the rotator. With a full height of tower, some
> of that torque gets taken up in the six-inch diameter drive pipe/coax
> line. But with the antenna on top of a building, there was only about
> 15 ft of drive pipe, so almost all the torque got transfered to the
> chain drive that was clamped on the bottom of the pipe. The clamp kept
> slipping and scoring the pipe... which needed a welder to come in and
> refill some of the lost metal. The costs of keeping the system charged
> with dry air were another recurring expense. It wasn't used often
> enough to justify the maintenance cost... so one day W3NRS's company
> lifted it off the building onto a nearby parking garage, cut it up, and
> hauled it to the scrap yard.
>
> The Weather Service's HF station had a club callsign, too: W3KWB
> (Kilowatt Weather Bureau).
>
> 73,
> -- Eric K3NA
>
> on 07 Sep 01 Sat 18:36 steve d said the following:
>> I drive a truck part time and came across this
>> (http://i118.photobucket.com/albums/o117/KC8QVO/random%20stuff/IMG_2427.jpg)
>> antenna on Rt. 227 in Leesburg, VA on my trip the past couple days. Does
>> anyone know whos it is and what it is for??? It is a log periodic and is
>> the largest rotatable antenna I have seen with my own eyes. The main boom
>> for the antenna is made out of triangular tower sectios. It appears to be
>> about 70 - 100' in length, from the perspective I had on it.
>>
>> The funny thing is.. I looked it up on google maps. You can actually
>> see the antenna and the shadow it, and the tower it is mounted to, cast
>> on the land HI. Pretty darn big! (I dont see the two other utility towers
>> in the sat view, they must be new).
>> http://maps.google.com/maps?f=q&hl=en&geocode=&q=leesburg,+VA&ie=UTF8&ll=39.102961,-77.543301&spn=0.002893,0.005021&t=k&z=18&om=1
>>
>> 73,
>> Steve, KC8QVO
>>
>>
>>
>> ---------------------------------
>> Luggage? GPS? Comic books?
>> Check out fitting gifts for grads at Yahoo! Search.
>> _______________________________________________
>>
>>
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>>
>>
>>
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