Installations – Page 9 – Engineering Radio

The Nautel XR6 AM transmitter

I’ve been away working in Burlington, VT (WVMT, 620 KHz, Burlington) for the last coupla, installing this nifty Nautel transmitter:

Nautel XL6 transmitter, WVMT Burlington, VT — Nautel XR6 transmitter, WVMT Burlington, VT

I like the Nautel units, both AM and FM; they are well-designed, well-built, rugged transmitters. I have lost track of how many of these units we service in the field, partly because they are becoming pretty much standard equipment at all of our installations.

Continental 315R-1 AM transmitter, WVMT, Burlington, VT

The transmitter it is replacing is a Continental 315R-1, which is based on the Collins Power Rock design. It is a PWM transmitter with a 15,000 volt power supply. In their day, these were not terrible transmitters, however, like their Harris MW-5/10/50 PDM brethren, frequent thorough cleaning is required to keep the dirt/dust from arcing over. Unfortunately, it is becoming more and more difficult to obtain parts for these units. This transmitter was installed in October of 1983, thus, almost thirty years of service is quite enough. This unit we did not cut up and scrap, rather, it is sitting by the back door, waiting for any takers.

Continental 315R1 modulator/RF sections — Continental 315R-1 modulator/RF sections

The interior of the Continental 315-R1 transmitter. Modulator section is on the left, RF section is on the right.

The good news is, WVMT is another one of those “successful AM station” stories. You know, the kind of station that has local programming, local sports, news, community presence and most importantly, makes money. For all those diligently studying the “AM Problem” for the up and coming NAB conference this April, here is a clue: It’s the programming…

Nautel XR6 transmitter, wvmt Burlington, VT — Nautel XR6 transmitter, WVMT Burlington, VT

This is the Nautel XR-6 on the air. Positive peaks, anyone?

We turned that down a little bit. Also, the station does not run AM stereo, the AM stereo mod monitor is simply a usable relic of a bygone era.

WVMT is noted as the first radio station licensed to the state of Vermont, signing on on May 10, 1922. It has a three tower directional array located down in the swamp. For some idea of perspective, it is 1,150 feet (350 meters) from the transmitter building to the center tower, the towers are 411 feet (125 meters) tall spaced 405 feet (123 meters) apart.

WVMT three tower directional antenna array, Burlington, VT — WVMT three-tower directional antenna array, Burlington, VT

WVMT antenna system from back of transmitter/studio building. That is a long walk over rough terrain in the middle of the night or anytime really, but especially in the middle of the night.

Moving the WRKI and WINE transmitter site

Blogging has been light due to workload being heavy, at the moment. We are engaged in moving transmitters out of this old house:

WINE 940 WRKI 95.1 former studio and transmitter site

Into this new transmitter building:

WINE WRKI transmitter building at base of tower

The former building was the original studio for WRKI, 95.1 MHz, which signed on in 1957. The co-located AM station, WINE 940 KHz, did not sign on until 1963. As such, the building is a little worn around the edges, so to speak. The FM transmitter has an auxiliary cooling device, for those hot summer days as the building itself is un-airconditioned:

WRKI Harris FM25K transmitter, circa 1986

The rest of the building is in similar condition. Ceiling tiles are falling off the ceiling and getting ground into the floor, junk is piled up in almost every corner, rodent feces, and the basement, don’t even get me started on the basement.

The basic floor plan for the new building is simple:

Right now, the preliminaries are being done, mounting the coax switch, running conduit, pulling wires, etc.

A few design notes:

This building is much closer to the tower, which is sited on a high hill (715 feet, 218 Meters) and sticks up 500 feet (152.1 Meters) above that. Basically it is the area lightning rod, thus special attention will need to be paid to grounding and bonding. I decided to isolate the electrical ground in favor of the RF ground for lightning protection. This involves putting toroids on the electrical ground conductors.
The building itself is shielded with continuous steel plating, but that has been cut in a few areas to install air conditioners. Those areas will have to be repaired and the AC units bonded to the steel plate.
Back up cooling will be in the form of a large exhaust fan and intake louver.
The tower itself is AM radiator for WINE. It is 170 degrees tall, which means high RF fields at the base, therefore good RF bypassing is needed.
The transmitter room itself is fairly small for what needs to go in there. careful design and placement is required.

Here are some in-progress pictures:

WRKI backup transmitter, Harris FM3.5K, coax switch in the background

The first order of business was retuning a Harris FM3.5K transmitter to function as the backup. The current backup transmitter is an RCA FM20E, which no longer runs. After the move is completed, that transmitter will likely be scrapped.

I attached super strut to the ceiling at four foot intervals. I used this strut to support the 4 port coax switch. All coax in the transmitter room is 3 1/8 inch hardline, which has a power rating of 40 KW. Since the transmitter power output is 20 KW, this leaves a lot of head room for problems. When working with a 3 1/8 inch coax, it is important to remember to cut the inner conductor 1 1/2 to 1 3/4 inches sorter than the outer conductor, otherwise the stuff doesn’t go together right.

The 30 KW air cooled dummy load was moved up from the other building and connected to the coax switch. This allowed the backup transmitter to be tested.

Three inch ground strap connects all the transmitters, racks, and dummy load to the station ground.

WRKI ground strap, new transmitter building

Electrical requirements are being met by a 400 Amp service backed up by a 120 KW generator. Once the conduit work is finished and all the wires pulled, the coax to the old building can be cut and brought into the new building, then the station can go on the air with the “new” backup transmitter.

The Nautel VS-2.5 FM transmitter

This is cute. A small (VS allegedly stands for “Very Small”) integrated 2,500-watt FM transmitter. This one we just finished installing as a backup transmitter for WSPK, on Mount Beacon, New York.

This site has a Nautel V-7.5 as the main transmitter. That unit is very reliable, however, this transmitter site is non-accessible 4-5 months out of the year due to ice and snow. The last time we had an off-air emergency due to a crippling ice storm, it took an entire week to clear away all the downed trees so we could gain access to the site via snowmobile. As such, every system needs dual or even triple redundancy. The lack of said redundancy has led to several prolonged outages in the past.

Last year, we were finally able to install a backup antenna after 63 years without one. This year, it is time to upgrade the rest of the backup equipment. The new auxiliary transmitter is connected directly to the auxiliary antenna via a five-port coax switch. This allows for the use of the dummy load for testing when we are present, but removes a potential failure point in the coax switch. There have been at least two incidences of the disk jockey accidentally transferring the transmitter into the dummy load when taking transmitter readings. Hopefully, this configuration will be fairly idiot-proof. I am making an interlock panel that will prevent both transmitters from being on the air at the same time.

This site is a work in progress.

The backup processor is at the transmitter site, the main processor is in the rack room at the studio. This works well because the main processor occasionally looses its mind and needs to be rebooted. It would be a significant pain to drive all the way up to the transmitter site just to reboot the processor. It might not happen at all during the winter. The backup processor has no mind so it is not an issue.

The VS transmitter is attractive because it has a built-in exciter that accepts composite, AES, or IP audio. The exciter also has a built-in Orban processor as an option. Thus, if it really hit the fan, we could use the LAN extender to get the audio to the site. Further, it could be addressed by any studio in the company WAN. Which is cool, when you think about it.

Nautel continues to crank out innovative, dependable products and there is nothing wrong with that.