Water and RF do not mix

Last year, the main antenna and transmission line for WSPK was replaced.  I was, therefore, somewhat surprised to hear that there was an issue with the new transmission line.  And yet, problems there are.  Most likely, some ne’er do well has shot the transmission line with a bullet making a hole, which, when it rains, allows in water.  Said water then accumulates in the bend at the bottom of the tower.  When enough water is present to fill the gap between the center conductor and the outer conductor, this happens:

Foward and Reflected power meters, WSPK, Mount Beacon, NY
Foward and Reflected power meters, WSPK, Mount Beacon, NY

For those of you keeping score at home, that’s 980 watts forward, 375 watts reflected or about 4:1 VSWR.  Obviously not a good load, in fact the transmitter shut down.  Fortunately, the backup transmitter and antenna system worked flawlessly.

This began happening last month, usually after a heavy rain storm.  Thus, I went out to the base of the tower and shook the transmission line and sure enough, water was sloshing around in there.  Last time time it happened, a tower crew was summoned to inspect the line.  Inspect it they did, but did they find any holes? No, they did not.  Perhaps the issue is with the antenna itself, in which case the entire thing will have to be removed from the tower and lowered to the ground.   In the mean time, my boss drilled a small “weep hole” at the bottom of the bend where the line comes off the tower.

I uncovered this weep hole and pressurized the line and viola, lots of water came out:

WSPK 1 5/8 inch air dielectric transmission line, Mount Beacon, NY
WSPK 1 5/8 inch air dielectric transmission line, Mount Beacon, NY

A bit unconventional, but effective nonetheless.  The first video is of the water dripping out:

The second video is of me walking back into the transmitter building to pressurize the line:

Everything is very noisy because it is Monday, when all the generators on site exercise. There are five diesel generators running while I was videoing recording this.

I would estimate about 6 ounces of water came out through the weep hole, most of it landing on the ladder underneath.  After the water was drained out, the transmitter came back on at full power and normal VSWR.

A temporary fix to get the station back on the air. The real repair work will begin when the antenna comes down to be inspected.

Update: The tower climbers did find a hole in the transmission line, just below the flange that connects to the antenna.  It looks like a pencil sized gash just before the line bends back to the tower.  Lightning? Rifle bullet?  Damage while installing?  We can’t really tell. They installed a patch over the hole which holds about 3 psi line pressure.  We then used a vacuum pump to evacuate the line, then recharged with dry nitrogen.

Regarding Pedro’s question below in the comments:  Since we found this problem quickly and were able to evacuate the line, there should not be any corrosion, that is our hope.  Time will tell

WKZE transmitter site

We rebuilt this station’s studio couple of years ago.  WKZE is licensed to Salisbury, Connecticut.  The transmitter is located near Millerton, NY and the studio is in Red Hook, NY.  Today, I had to go to the transmitter site to fix a problem with the station’s processor.  While there, I snapped a few pictures:

WKZE, 98.1 MHz, Millerton, NY
WKZE, 98.1 MHz, tower near Millerton, NY

The WKZE single bay antenna is mounted on the left hand tower.

WKZE single bay Shively 6810 antenna
WKZE single bay Shively 6810 antenna with Radome

The transmitter is a CCA FM3000DS, made new in April, 1970:

WKZE 98.1 MHz CCA transmitter
WKZE 98.1 MHz CCA FM3000DS transmitter

The CCA designs are dirt simple. Grounded grid, driven with an external solid state amplifier that is a modification.

WKZE CCA transmitter, 42 years on
WKZE CCA FM3000DS  transmitter, 42 years on
WKZE CCA transmitter name plate
WKZE CCA transmitter name plate

As you can see, this transmitter was originally manufactured for WHVW-FM, which is now WCZX.  The station has a large, mostly cult following throughout the mid Hudson valley.  Even though it is a 3,000 watt class A station, it’s coverage carries far beyond it’s theoretical 60 dBu contour:

WKZE predicted 60 dBu contour
WKZE predicted 60 dBu contour

This is because the station is in mono.

Water and transmitters do not mix

This incident happened a few years ago.  I thought I had lost the pictures of the disaster, but I found them this morning on my thumb drive. Hooray!  This occurred one morning just before Christmas after the area received a snow/ice/rain storm.  The gutters on the old ATT long lines building clogged with ice and the water on the roof built up.  Unfortunately, the transmitter was installed directly below a disused exhaust stack for the former backup generators.

I received the off air call from the morning show while I was driving to the office.  I diverted and went to the transmitter site and found water pouring into the top of the main transmitter.

WBPM transmitter room flood
WBPM transmitter room flood

Thus, water ran down directly into the top of the QEI FMQ-3500 transmitter (transmitter was upgraded to 6 KW). Unfortunately, high voltage and dirty stack water do not mix. The combination of sooty, iron laden water and the B+ damaged much of the transmitter circuits beyond repair.  The main transmitter is on the right, the backup transmitter is on the left.

I inspected the backup transmitter, also a QEI FMQ-3500, and it seemed to me that no water made it into the unit.  I rigged the tarp to ensure that none did, which was a very pleasing bit of work, what with the cold, smelly, dirty diesel water dripping on my head and running down my neck and back.

Top of WBPM QEI FMQ-3500 transmitter
Top of WBPM QEI FMQ-3500 transmitter

The 1 5/8 coax switch was also damaged:

WBPM 1 5/8 coax switch
WBPM 1 5/8 coax switch

As was the remote control in the equipment rack:

WBPM Gentner remote control
WBPM Gentner remote control

Fortunately, the backup transmitter ran, although I pressed the plate on button with a dry wooden stick while standing on a dry, non-conducting ladder.   Even so, I still felt a little trepidation holding that stick.

WBPM Saugerties, NY Nautel V-7.5 transmitter
WBPM Saugerties, NY Nautel V-7.5 transmitter

It took almost a year, but finally the insurance company for the building owner came through, and a new Nautel V-7.5 transmitter was installed.  I believe this is the last V transmitter Nautel made.  We moved the transmitter location across the room, not under the old generator stacks.  We also removed the generator stacks and patched up the roof with hydraulic cement and roofing tar.  By the way, that yellow color should look familiar to anyone who ever worked inside of a Bell Telephone System building.

 

Backup cooling

One of the issues that I have seen at many transmitter sites is inadequate cooling. Time was, when mostly tube transmitters were in use, a simple fan connected to a thermostat was all that was used to cool most transmitter sites.  Even then, however, that setup was lacking for several reasons.

Those reasons are:

  • The amount of cooling provided was limited by the amount of heat in the outside air.  On cool winter days, this is not a problem, but on hot, sticky summer days it could be.
  • No removal of humidity from the transmitter room was possible.  This often lead to excess oxidation, corrosion of metal parts and so on.
  • No matter how much filtering was used, bugs, dirt and other debris was sucked into the fan, making transmitter room cleaning a chore.

With solid state transmitters, air conditioning is required.  Solid state transmitter devices are far less rugged than tubes when it comes to heat.  In a high heat situation,  a tube transmitter will keep running until its control circuits malfunction, or it catches on fire.  A solid state transmitter will crash long before either of those things happen.

Air conditioners should be adequately sized for the heat load plus a little extra.  That information can be found in a previous post: A tale of two air conditioners.

As we all know, equipment malfunctions.  When an air conditioning system goes bad at a transmitter site, things start to happen fast if there is no backup.  That is when a backup cooling fan can save the day.  A good rule of thumb for sizing a cooling fan is to exchange the total volume of the transmitter room every two minutes accounting for resistance from louvers and intake openings.

3200 CFM cooling fan, WHUD transmitter site
3200 CFM cooling fan, WHUD transmitter site

This fan is connected to a 120 volt contact on a thermostat attached to the ceiling of the transmitter room.  The thermostat is set for 90 degrees, which gives a good bit of headroom for the air conditioners to maintain the room temperature, while turning the fan on before the room gets too hot. It is also important to monitor the room temperature via remote control.  Having an alarm contact connected to the fan thermostat is also a good idea.

There is no such thing as too much backup.  Installing a louvered cooling fan affords a little bit of extra insurance.