Loran-C  Raymondville,  7980-X / 9610-Y

These are pictures I took on a visit to the Loran-C station in Raymondville, Texas, in 1984.

Click to enlarge:

Click to enlarge This is the outside of the building.  A typical military building, nothing fancy, but it's well maintained.

Click to enlarge Inside the building, the two largest rooms (as I recall) are the transmitter room and the clock room, shown here.  These racks contain the atomic clocks for the station as well as the brains of the transmitter, and a receiver and monitoring scope to observe the other stations in this Loran-C chain — by listening between the transmitted pulses of this station!  In ham radio circles, this is called "full QSK".

The atomic clocks are the same make and model as the three clocks at the WWV transmitter site.  I suppose GPS timing has probably taken center stage at this station by now.  Notice also that the racks have side panels, and there are small air gaps between the racks.  In most radio facilities with rack-mounted gear, the racks are side-by-side.  Keeping them separate probably helps isolate the atomic frequency standards from nearby heat sources.

Click to enlarge The transmitter is all solid state, and consists of a number of large modules, each contributing power which is combined into the antenna feed.

Click to enlarge In extra spaces around the transmitter there's somewhat of a repair shop.

Click to enlarge The building is protected by a Halon fire protection system, which was pretty advanced technology in 1984.  Today this kind of system is fairly common at transmitter sites, gas stations and other places where quick waterless response to fire is necessary.

Click to enlarge This is the heart of one of the transmitter modules.  Each of these modules puts out one half cycle of RF, and the amplitude of the pulse is different for every module, which allows precise control of the shape of the transmitted pulse.  The pulse is generated by charging a capacitor bank and then firing a big SCR (in the middle of the module) to make a big current pulse on one side of a transformer.  Very clever.  Each module weighs several hundred pounds, but there is a little crane with which the crew can do the heavy lifting, when it becomes necessary to change out a module.  I forgot to ask how many on-line spare modules there were.

At the time of my visit, the station was designated as 7980-X.  Today it is also serving as 9610-Y, so I imagine the transmitter is really busy now.

Click to enlarge The base of the tower is shown here.  Of course the entire tower rests on a big insulator, but the three legs of the tower come straight down, so that it is easier (I was told) to replace the base insulator, if necessary, by using hydraulic jacks to lift the tower!  There are two lighting transformers (interconnected rings which don't quite touch), for transfer of RF-isolated AC power to the tower lights.  This is fairly standard equipment at AM radio stations, but I don't think I've ever seen a tower with two of these transformers.  (A much better photo of such a transformer is shown here.)

Click to enlarge A tower of this sort always has a spark gap for additional lightning protection, but it usually consists of two metal balls about ¾ inch apart.  (Like this.)  This one has a metal bowl over a grounded ball.  They tell me this style performs better in wet climates, and that's good because Raymondville is in a semitropical area of south Texas.

Click to enlarge The insulated feed comes out of the building and connects directly to the tower.  While taking these pictures, we were asked not to touch anything, because there's 30,000 volts of RF on all the hardware at the base of the tower.

Click to enlarge The tower is about 700 feet tall and has a giant capacity hat on top, consisting of twelve wires that are hundreds of feet long.

This tower is located at 26° 31' 55.141" N. / 097° 49' 59.539" W.

I'm assuming that even in today's political climate, with all the talk of terror alert levels and homeland security, that it's okay to publish this information.  After all, these pictures are twenty years old and this navigation system has been largely displaced by the Global Positioning System.

Now that I have a much better camera, I should return to Raymondville and see if I can take some more pictures; however, I doubt if anybody could just walk up to a facility like this today and start asking questions and taking pictures.  Those days are over.

Updated 6/22/2006:
Click to enlarge
I found another photo in the archives, scanned it, and corrected the white balance with Photoshop.

More information:

An apparently identical transmitter is located at the Loran-C station in Malone, Florida.

Loran-C - Transmitters and Coverage.

Loran-C - Signal Characteristics.

New Potential of Low-Frequency Radionavigation in the 21st Century.  The PhD dissertation of a fellow in the Netherlands whose main point (apparently) is that it is prudent to maintain an alternative to GPS — in a completely different part of the RF spectrum — just in case.

Update:  The station went off the air in February, 2010, according to the Raymondville page at Loran History dot info.

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