FM transmitter site – Engineering Radio

The GatesAir FLX-30

This is the second time I have installed one of these liquid cooled transmitters. This time, it is for WVPS in Burlington, VT. WVPS is the flagship station for Vermont Public Radio. The station is a full class C, a rarity in the North East. The transmitter is located on Mount Mansfield giving it a HAAT of 2,717 feet (828 Meters), which is a good ways up.

This transmitter replaced the previous backup transmitter, a Harris Z16 unit from the early 00’s. There was nothing really wrong with this unit, it just was not a full power backup.

The new transmitter came in two pieces, which is typical for the 30 and 40 KW GatesAir liquid and air cooled transmitters.

New Transmitter, being placed in Radio Transmitter room

For the cooling part of this installation, 1 1/2 inch type M copper pipe was used. This matches most of the other TV transmitters down the hall. In the same building are the transmitters for WCAX-TV, WPTZ-TV, WFFF-TV, and WVNY-TV.

FLX-30 Heat Exchanger, outside with all the others

Liquid cooled transmitter piping, WCAX’s left pair, WVPS right pair

Air purge valve, sight glass, cross connect and distribution manifold, above the transmitter

The highest point in the liquid cooled system is the air purge valve and distribution manifold just above the transmitter. From here, everything slops down to a few low points; the heat exchanger outside, the pump station and the power blocks. This is to make it easier to drain, if that ever needs to happen. There is also an air inlet valve to aid in draining.

All of the cooling work is controlled by the pump station. The fans are connected to VFD modules, which control the flow of air though the Heat Exchanger.

All of this plumbing work was greatly sped along with the use of this Pro Press pipe press tool. This thing is great! No more sweating connections. Dry fit a section to make sure that it is all cut correctly, then go to work with this and it is done in a matter of seconds. Of course, there are no re-dos, so the dry fit procedure is a little more important.

Prior to filling with with Heat Transfer Fluid (50/50 water/antifreeze mix), the system was first pressure tested with air, then filled with clean water for a 12 hour flush. The water was drained out and the filter screen cleaned, then it was filled with the appropriate Heat Transfer Fluid.

Testing into dummy load, TPO is 25,995 watts with -14 dBc HD Radio

Final system checks, remote control test, and HTF top off and the transmitter is ready to go pending the HD Radio installation.

WEZF and WVPS four bay three around panel antenna

The Unglorious task of Vermin Control

Warm, unmanned buildings in the wilderness are very attractive to all sorts of uninvited guests; mice, rats, snakes, insects, etc. Unfortunately, these can do damage to equipment, as evidenced here:

Mouse infested power panel, remote transmitter site

Thus, some steps need to be taken to secure transmitter sites, generators, outbuildings and even vehicles from mice in particular. Mice can squeeze into a hole that is .7 inch (17 mm) in diameter when they are full grown. In many transmitter buildings, this leaves lots of opportunities; coax feed through ports, ingress holes drilled for wires, electrical service entrances, cooling fans, gaps under doors, soffits, etc.

Many people simply call the pest control people who will come and put poison out. That does not solve the problem and can in fact make it worse. If the poisoned mice go outside to die, they are eaten by the snakes and birds that naturally control mice in the wild. Those animals then die from the poisoned mouse. Meanwhile new mice are being reproduced every 20 days or so. Fairly quickly, the bait is consumed, the mice no longer have any predators to naturally keep the population in check and there is a mouse explosion.

Hole in cinder block building covered with aluminum rack panel blank — Large hole, formerly a vent for propane heater, covered with aluminum rack panel black.

The best way to keep them in check is to seal up building as much as possible. For some reason, coax entry ports are often left open. This is very easy to fix and whenever tower crews are running new lines, ensure that they apply the correct boot for the port and line.

Replacement door jamb — Deteriorated door jamb replaced with pressure treated wood

Another thing that happens; door jambs deteriorate or the bottom of steel doors begin to rust away. This opening is very attractive to insects, snakes, mice and even plants.

Screen covering generator ventilation opening — Chicken wire screen covering generator ventilation opening

Generator radiator opening covered with chicken wire — Generator radiator covered with chicken wire

Generators need special attention. Radiator and ventilation openings should be covered with chicken wire. This can be attached to the metal housing with self taping screws and fender washers. Be careful and look inside of the housing to make sure that the area inside the housing where the screws are being applied is clear of wires and hoses.

Stainless steel pot scrubbers filling space around conduit and pipes — Stainless steel pot scrubbers filling gaps around conduit and fuel line

Ingress for fuel, control and electrical conductors need attention as well. I found stainless steel pot scrubbers to be effective for filling gaps around these conduits and pipes. They are available on Amazon or many other places.

New Power Panel, an expensive lesson in pest control

Other openings can be filled with a combination of pot scrubbers and spray foam. Using spray foam alone often does not work, as the mice will crew through it.

I also keep a can or two of bee spray at most sites. Bees, hornets and paper wasps love to make nests in propane tank fill covers, ATU’s, under air conditioning units or anyplace else that is sheltered from rain.

Incandescent Indicating lamps

What is wrong with this picture?

It is a little bit blurry, but the real problem is that none of the indicator lamps on the phasor or antenna monitor are working. Those little incandescent 387 bulbs burn out frequently. It is difficult to tell, at a glance, whether the phasor is in daytime or night time mode. One also cannot tell which tower or mode is selected on the antenna monitor.

It is a small job to replace them, but it does take some time. They currently exist in older transmitters, studio consoles, meter back lighting, and other control indicators. Since I began working in radio, I have replaced hundreds of these little lamps. I would rather spend my time on more interesting projects.

The 387 bulbs cost about a dollar each and last less than a year, in most cases. Fortunately, there is a solution to all this. Enter the based LED replacement lamp. These little guys have the long life of an LED (100,000+ hours) in a package that is a direct replacement for the Incandescent lamp. They run about $5.31 each.

Dialight makes a very handy cross reference:

Dialight Incandescent to LED cross reference

The entire cross reference section is three pages long and is a part of their PMI catalog. The full cross reference .pdf can be found here.

Those Dialight LED lamps are available from Mouser, Allied and Newark Electronics.

Time is money. There are much better things to be doing than going around replacing incandescent indicator bulbs in various pieces of equipment. At the same time, it is important to know what the status of that equipment is at a glance, which is the reason for using any type of indicator in the first place. Using drop in replacement LED indicating lamps with certainly save time and money in the long run.

Something is not right

The Goddamnitnotagain edition:

PA module with burned open output transformer

I went to do maintenance at one of our sites and noticed that a certain transmitter was running at half power. Followed the path of the fault log and found this. When I mentioned it to the station staff, they said, “Yeah, we noticed it sounded a little funny…”

This is the second time this has happened with this particular transmitter. In any case, this is what I get paid for, so I am certainly not complaining. If only every problem where this easy to find.

When I get back out there to replace this, I will bring out my network analyzer and sweep the antenna and transmission line to make sure there are not issues with that. In addition, I will double check all the grounding to make sure the copper thieves have not made off with any critical components like the ground buss bar or #2 solid down lead wires.