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Repairing the Nautel VS2.5 transmitter

LBA Technology AM antenna systems, RF
shielding, and test equipment

The newish Nautel VS2.5 transmitter installed at WJJR had an RF module failure. This particular model transmitter does not have slide in RF modules as other Nautel transmitters do.  To fix this transmitter, it has to be pulled out of the rack, flipped over and opened from the bottom. The module replacement is very straight forward, there are five solder pads that connect to wires carrying the input, output, power supply and bias voltages.

Nautel VS2.5 transmitter RF modules and combiner

Nautel VS2.5 transmitter RF modules and combiner

The troubleshooting guide gives good instructions on how to check the PA MOSFETS with a DVM. I found that 1/2 of the device in PA1 was bad:

Schematic Diagram, NAPA31

Schematic Diagram, NAPA31

All in all, not a very hard repair. This was under warranty, so a replacement RF pallet was sent to the station without charge. The problem is more about where the transmitter is located:

Killington Mountain, Killington, VT

Killington Mountain, Killington, VT

Killington Peak is the second tallest mountain in Vermont, topping out at 4,235 feet (1,291 meters). In the winter, one can take the chair lift to the top. In the summer, the road is drivable with a four wheel drive. In those in between months, access to the top can be very tricky at best. We had a pretty wet spring this year, so the roads up the mountain are just now becoming passable for vehicles.

Even after reaching the parking lot, there is still a 10 minute walk to the peak, another 200 or so feet up a steep, rocky trail.

Further complicating things, this transmitter is wedged into this little shack, which holds; a BE FM3.5A transmitter (defunct WJJR), a Harris HT3 transmitter (WZRT), an ERI combiner, two racks of equipment (STL’s, Exciters, remote controls, etc) a backup QEI transmitter, an Onan generator transfer switch:

Killington Peak fire tower, WJJR WZRT transmitter building

Killington Peak fire tower, WJJR WZRT transmitter building

Both stations run into this ERI half wave spaced antenna:

WJJR WZRT ERI antenna

WJJR WZRT ERI antenna

It is very tight in this transmitter room. There is a new tower on Killington Peak, which is still under construction. At some point, the plan is to move into the larger building next to the new tower.

Killington Peak tower

Killington Peak tower

On a clear day, the view from the top is spectacular. On this day, the peak was in the clouds, so not so much:

Killington Peak view

Killington Peak view

It is a great site, the HAAT is 2590 feet (790 meters) and the stations carry forever on relatively low power outputs.

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5 comments to Repairing the Nautel VS2.5 transmitter

  • Somewhere I have a picture of that two bay with a huge chunk of Rime ice on it. I’ll have to find it, it’s kind of old now.

  • Mike Seguin

    I remember fondly? doing the original install with WJJR. I was working for James Broadcasting WVMT/WRUT/WSYB. Spent a summer cramming things into the little building there…. The particular ERI chosen for the site was mostly for survivability. G5 bays as I recall. Didn’t need the power handling, but rather mechanical strength and bandwidth.

    Killington is a fun place. There used to be a pair of guyed towers there. In Feb of 1981 there was a small “incident” with one of the towers. Here’s a pic of it taken as we headed up the Mtn.

    http://users.burlingtontelecom.net/~n1jez@burlingtontelecom.net/images/killington.jpg

    Opps – snapped leg on the left most tower. It was leaning into the other tower.

    One of the most daunting issues with the install was an intermod problem with the Dept of Public Safety microwave system. The 2 FM’s were on 97.1 and 98.1 The DPS microwave had a ‘pilot’ signal in the baseband that controlled switching to backups in case of primary failure. Guess what the freq of the pilot was? Yup, 1 MHz. We did conquer it with filtering in their microwave gear.

    Mike

  • Baylink

    perhaps this is a stupid question, but would it be unreasonably expensive for the radio station to talk the people who operate the chain lift and turning it on, given the circumstances?

  • Scott Nielsen

    Would anyone in this forum be opposed to a proposal I’m putting together, addressed to the US Army Corp of Engineers, calling for the removal of the old fire tower on Killington Peak? The summit is struggling in its current state of junkyard status. Fire tower removal would not interfere with radio operations, and I’d like to elevate the standard of environmental stewardship where possible. Killington Resort has gone to great lengths to operate with an environmental consciousness, and it is my understanding that the peak territory is actually beyond their domain.

  • Paul Thurst

    Scott, I have no problem with it, so long as the radio stations are allowed to mount their antenna on the new tower.

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