Paul Thurst – Page 107 – Engineering Radio

The General Electric XT-1-A AM transmitter

I found this photograph in a filing cabinet the other day as a part of a sales proposal dated 1948. I have never seen one of these in the field. They look like very sturdy units:

General Electric XT-1-A Standard Broadcast transmitter

Back in the day when AM was king, no expense was spared on transmitting equipment. I remember the GE BTA-25 transmitter from the same era, it was built like a tank. Once, while we were repairing the Harris MW-50A main transmitter, the old GE burped, sputtered, and threw an IPA overload, then returned to air. I looked in the IPA cabinet and found a mica capacitor had been blown in half. It was in the tuning circuit, but apparently, there was still enough capacitance in the circuit for the transmitter to keep running.

This unit looks similar to that one. The simplified schematic:

General Electric XT-1-A schematic diagram

Like other 1 KW AM transmitter designs, this unit uses the venerable 833A triode. There are some advantages of this tube, as extra circuits for PA stage neutralization are not needed. The full sales brochure can be found here (medium-sized .pdf). These were manufactured in Syracuse, NY.

The asking price in 1948 was $8.730.00, tax and shipping extra.

The PIROD PRLC-A tower lighting controller

PIROD tower company has been around for a while, thus there are likely many of these tower light controllers out in the field. They perform a vital service in controlling and monitoring tower lights at remote transmitter sites maintaining a safe operating environment for aircraft and compliance with FCC rules.

PIROD was sold to Valmont in 2004, Valmont no longer manufactures or supports the product. All is not lost, however, as XCEL Tower Controls does support it and parts are still available through them.

These units were fairly rugged, had good surge suppression on the incoming AC lines and are designed for easy access to service parts.

PIROD PRLCA tower light controller, WRKI Brookfield, CT

This particular controller is being installed at WRKI in Brookfield, CT. We are adding toroid cores to the tower lighting circuits coming off of the tower because the last controller has been mostly destroyed by lightning. It is a tall tower, on top of a tall hill, thus it gets struck by lightning many times over the course of a year.

The block diagram looks like this:

Click for higher resolution.

The basic schematic looks like this:

Click for higher resolution.

The entire manual can be found here, (medium sized .pdf) courtesy of John Brickley of EXEL tower controllers.

The Rabbit Hole

The internet is a wonderful technical achievement. It has truly changed the course of human history in ways incalculable. The amount of information available to anyone with access is simply astounding. Then there is this:

I am supposed to be doing research for my technical writing class, but I keep getting sucked back in. Some of these are quite funny:

GAH! Someday, if I could figure out how to get that cloaking device to work, I would like to seek into all those conference rooms and replace the standard issue motivational poster with this one:

And the minutes still tick by, with my paper undone. These are from despair.com,

The professor is going to have my butt.

It has been relatively light blogging these last few weeks, for several reasons; some of them obvious, some of them not so much.

WVTQ Mount Equinox, Vermont

The transmitter for Vermont Public Radio, WVTQ 95.1Sudbury is located on Mount Equinox, near Manchester Vermont. Mount Equinox is one of the better mountain top transmitter sites to get to as it has a good access road, no jeep trails through the woods or ski lifts, etc. The Summit is 3,580 feet (1,175 m), which is the third-highest peak in the green mountains. On a nice day, the view from the top is spectacular:

The southern view with US Route 7 cutting through the valley below.

WVTQ is a part of VPR’s classical music network. They had a Nautel VS-1000 that had developed issues with the directional coupler. This unit was repaired and re-installed:

WVTQ Nautel VS-1000 transmitter, Mount Equinox, Vermont

The transmitter has a 7/8 EIA flange on the back, which had an elbow, then an adapter to a type N connector all unsupported. My boss felt that perhaps that perhaps too much weight on the EIA flange caused the crack in the directional coupler.

WVTQ transmitter racks and STL equipment

The transmitter site used to be in the basement of the hotel, but as that building no longer exists, it was moved over to the former RADAR site. The RADAR site consists of four 80-foot towers arranged in a square around a building. These towers now support two-way radio equipment and the like

WVTQ transmitter site, Mount Equinox, Vermont

Your author (left) with Rich Parker of VPR discussing the finer points of GPS antennas.

Ladder to the top of one of the towers.

Hang Glider's view, east side pulloff, Mount Equinox, Vermont — Hang Glider’s view, east side pulloff, Mount Equinox, Vermont

View from the turn-off on the east side of Skyline Drive. Known as “hang glider’s view” with good reason. This is on the saddle that connects little Equinox with big Equinox.

On a nice day, such as yesterday, it is very pleasant. When the road is covered in ice and snow, not so much.