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Somewhere in Utah, a phone company is missing it’s microwave site…

I followed this a link to this site called “SurvivalRealty.com” and saw this article about what looks to be a former ATT microwave relay site in Utah turned into a residence.  The site is much smaller than the former ATT site in Kingston that I profiled in this post.   Still, that is a Western Electric tower and those are KS-15676 antennas.

Former ATT microwave site turned into a residence

Former ATT microwave site turned into a residence

If I were that guy, I’d take those antennas down a scrap them.  Looks like the wave guides are already gone.  I might have tried to put some windows in while I was renovating it.  It would drive me crazy to live in a house without any windows.  I guess if one where waiting for the big one, windows might not be a desired feature of a survival bunker.

I wouldn’t really call it a “communications bunker” though.  I’ve been in communications bunkers, they are mostly underground and are much more robust than that building.  Still, it is built better than an ordinary commercial building or a regular house.   It would take a special person to live out in the middle of nowhere like that.

Working with Tower Companies

Almost all radio stations use a tower of some sort to support their transmitting antennas.  These towers need maintenance from time to time and only qualified people should perform maintenance on towers.  Hence, the tower company is formed.

405 foot guyed tower with ERI FM antennas

405 foot guyed tower with ERI FM antennas

Over my years of experience, I have dealt with many different tower companies, from one man operations to big corporations that have multiple crews out in the field on any given day.  I have discovered that not all tower companies are created equal.  Not only do tower climbers need to be in good physical shape and be trained correctly in all tower climbing safety procedures,  they also need to be good mechanics so they can actually repair things on the tower.   Climbing a 470 foot tower to repair a strobe light is all well and good.  Once the climber gets to the strobe light, he needs to be able to disassemble it without dropping parts or breaking things, trouble shoot if needed, install new parts and re-assemble the unit, again without dropping or breaking anything.

Applying a RF connectors, installing a FM antenna or STL antenna, repairing light fixtures or conduit all require some amount of manual dexterity and concentration.  Assembling high powered antenna requires close attention to detail.  Any pinched O rings, cross threaded bolts, bent bullets and the antenna will have problems, likely at the worst possible time.

The sign of a bad tower company is if it’s climbers cannot carry out those tasks with one or at most two climbs.  I have a situation on a tower where our FM station is a tenant.  The tower has a strobe light failure near the top of the tower where our FM antenna is located.  They have climbed the tower no less than four times to repair this, and it is still not fixed yet.  Each time they climb, the station has  to reduce power to protect the tower climbers from excessive RF exposure.  Each climb it takes them several hours longer than anticipated to finish their work.

A good rule of thumb, If the defective part cannot fixed in the first two climbs, then the entire strobe unit should be replaced on the third climb.  Even though the strobe units are expensive, by the time they get done paying for all this tower work, they could have bought two new strobes.  Today will be the fifth climb and there is no guarantee that it will be fixed.

I advised the tower owner that they should be looking around for another tower company because these guys aren’t exactly setting the world on fire.

Cold War Relic, ATT long lines microwave site Kingston, NY

Once upon a time, in the not too distant past, all long distance communication in the US was handled by one company, AT&T. There was no other company that could transmit data over medium to long distances. The breath and scope of their communications network is not understood by most people these days. Most people know that AT&T handled long distance telephone calls for the Bell Telephone System until the Bell breakup in 1984. However, AT&T did a lot more than long distance phone.

For example, if you watched the network news or network TV show anytime before 1980, it was likely brought to you via AT&T microwave system, known as AT&T long lines. Listen to the news on the radio, same deal. Before the wide spread use of communication satellites and fiber optics, the AT&T microwave relay network was the only way to get various types of electronic media signals from one place to another.

Beginning in the late 1980’s, competing local and long distance telephone companies began installing fiber optic cables between company offices. That coupled with the increased use of satellite systems for mass media video and audio delivery services made the huge AT&T microwave network obsolete. Some of the old microwave sites that are located in down town areas have been reused by local phone companies and cell phone providers. Many of the rural sites now sit empty.

ATT long lines microwave site with towers

ATT long lines microwave site with towers

This is the former AT&T microwave relay site located near Kingston, NY. It is now owned by American Tower, Inc. There are two towers behind the building, only the tower on the right has a few active communications antennas on it.  The taller tower is 190 feet tall and was built in 1957.  The shorter tower is 120 feet tall and was built in 1961.  Both towers and everything on them was made by Western Electric, the same company that manufactured the telephone sets.  Chances are, Western Electric contracted the actual manufacture of equipment out to others, then billed AT&T, their parent company a markup.  Something that would make all MBAs proud.

Western electric 190 foot tower, built in 1957

Western electric 190 foot tower, built in 1957

This tower was built in 1957.  The structure and galvanizing are still in excellent condition.

The large antennas you see on the towers are microwave horn antennas. They are no longer in use. Several transmitters and receivers would have been connected to each one of these antennas by use of RF multiplexers. Each microwave transmitter/receiver would have had several data channels. Generally, this was C Band microwave equipment, so it was in the 4, 6,  and 8 gHz frequency range.

Western Electric KS-15676 microwave antenna

Western Electric KS-15676 microwave antenna

All of this telephone traffic was transmitted on digital data channels un-encrypted. Many have argued that this allowed the government (most notably the NSA or National Security Agency) to intercept and listen to most domestic long distance telephone calls within the US. There is a book called Puzzle palace by James Bamford if you are interested in NSA history. It was written more than 20 years ago, so it doesn’t really apply today, but it is an interesting look at what the government was up to.

The building itself is huge, the first floor is 16,000+ square feet and the second floor is 10,000+ square feet. Only about 1000 square feet of this space is actively being used.

I believe this building was built in the late 1940’s or early 1950’s, just as Kingston was growing into a major IBM manufacturing site. The IBM buildings are located a few miles to the south east of this location, they are another cold war relic for discussion later. The IBM buildings were a major computer research and development site in the 1950’s until it closed in 1992. It was assumed that the Soviets had several spy satellites trying to steal secrets from the area, and the IBM facility was a primary nuclear target.

Blast baffle for generator cooling air intake

Blast baffle for generator cooling air intake

The microwave relay site has 12 inch re-enforced concrete walls. The ventilation air intakes have blast baffles to prevent a pressure wave (from a nuclear explosion) from blowing the ventilation equipment off of its mounts.

pnumatic actuator panel, seals all outside openings with steel blast doors

pnumatic actuator panel, seals all outside openings with steel blast doors

All of the outside openings were able to be sealed with steal blast deflectors using a pneumatic control panel located in the control room. There was a five minute timer, presumably to allow the HVAC units to be secured before the doors where closed. They where heavy gauge steel shutter designed to deflect the pressure wave of a nuclear explosion. Since this is an earlier building, it is likely that it is built to a 2 PSI pressure wave spec.  Newer buildings were built to 20 or even 50 PSI.  This microwave relay site would not have withstood a direct hit from a nuclear warhead, especially the higher yield warheads that came later on.

Water chillers for HVAC system

Water chillers for HVAC system

There where three large water chillers to provide cooling to the HVAC units. Since this was the 1950’s all of the electronic equipment would have had tubes, which would have generated a lot of heat while operating. There were two loops in the HVAC system. The refrigerant loop, which ran between these units and the huge condensers on the second floor roof, and the chilled water loop which ran between these units and the air handlers located in various parts of the building.

There is a bomb shelter in the basement. I found a couple of olive drab cans of civil defense water laying around. The lights were not working at the bottom of the stairs, so I chose not to go into the bomb shelter itself.

Stairs going down to the bomb shelter

Stairs going down to the bomb shelter

“Okay everybody, the missiles are on there way, so lets head down these stairs and pray”

There where two diesel generators, one was 325 KW which could run the entire building. The other was a 200 KW which could run the critical building functions. The fuel storage consisted of two 10,000 gallon tanks buried in the ground outside. Each steel fuel tank had a cathodic protection circuit. Basically a small negative electrical current was passed to the steel tank to keep it from rusting. Apparently it worked because when the tanks were removed in 2000 after 45 years in the ground, the primer was still on the outside of the tank.

Electrical switch gear, part of power company sub-station

Electrical switch gear, part of power company sub-station

The building has it’s own power substation. The electric from the utility company comes off the pole at 13,800 volts and goes to a large step down transformer on a pad outside. From there 480 volts is fed to this switch panel, where it is routed to motors loads or other step down transformers within the building.

Frame room floor, equipment removed

Frame room floor, equipment removed

On the main floor, there were rows and rows of wire terminal equipment, microwave transmitters, receivers and data and RF multiplexers in racks. The room in the above picture is about 10,000 square feet, there is another 6,000 square feet beyond the plastic heat barrier. This microwave gear received and transmitted data from Albany and Germantown to the north; Poughkeepsie, Putnam Valley, Ellenville, and Spring Valley to the south. All of that equipment is gone now, replaced by empty space.

Now the whole place is a little creepy.

There are about 500 copper wire pairs of telephone cable that came into various parts of the building to carry the DS-1 and DS-3 circuits that interfaced with the TELCO office in Kingston.

All in all, this was a serious building, no expense was spared in the construction and equipment outfitting.  The entire building is shielded with copper mesh screen embedded in the concrete walls.  There where redundant systems on top of redundant systems, something that you do not see these days, even in government buildings such as emergency operation centers (EOCs) and 911 call centers.

Matching an AM transmitter to a tower

This was a fun little project I was involved with last year.  Diplexing two AM stations to a single tower.  This particular tower was brand new, replacing an older tower that was rusting from the inside out.  As such, it had slightly different characteristics than the old tower, so it was a whole new project.  Fortunately, the old Antenna Tuning Units (ATU) were made by Kintronics, so they had plenty of head room on both side of the circuit for matching purposes.

The replacement tower is up, the new unipole antenna has been installed and now it is time to match the transmitters to the tower. This involves using some math. At some point in radio history, someone decided that all transmitters should have an output impedance(Z) of 50Ω (ohms). Impedance in an alternating current (AC) circuit (all radio frequency is AC) is like resistance in a direct current (DC) circuit. The only difference is impedance requires the use of the Z axis to calculate. You remember 9th grade algebra and the Cartesian Coordinate graphing system, the X and the Y axis. Looking down on the X and Y axis, the Z axis would be stick straight up, which makes it a three dimensional problem.

Station number one, broadcasts on 980 kHz at 5,000 watts. The tower is 240 feet tall which is close to 1/4 wave length, nearly ideal for an AM station. Using a Delta Operating Impedance Bridge (OIB-1) and a Potomac SD-31 frequency Generator, I measured the impedance at the base of the tower. On 980 khz it is 74Ω with +j160 reactance. Using the ohms law pie chart, anything can be  figured out about electricity:

ohms law pie chart

ohms law pie chart

Therefore, the base current will be I=√(P/R) =√(5000/74) = 8.3 amps. The voltage will be E=√PxR =√(5000×74) = 608 Volts.

A bit about reactance; it is noted by using the letter j, which indicates it is an imaginary number. Basically in an AC circuit, there is inductance and capacitance. They are the reciprocal of each other, sort of (this could get into a long, long post if I have to explain the roles of inductance and capacitance in and AC circuit). Reactance is an undesired inductive or capacitive component that has to do with the lead or lag time between the voltage wave form peak and the current wave form peak. In standard utility company parlance it is know as the “Power Factor”. In RF circuits it causes inefficient power transfer and it needs to be canceled. A +j value indicates that the reactance is inductive, and therefore needs to be canceled out with a capacitor. A -j value indicates the reactance is capacitive and needs to be canceled out with an inductor.

Then there is the difference in impedance, the transmitter and transmission line is 50Ω and the tower is 74Ω. Enter the antenna tuning unit (ATU). The ATU matches the base impedance of the tower through the use of a T network:

To determine the value of each leg of the T network, we need to employ math again. Here is where the details will catch up with you. Remember, there are two stations on this tower, a 980 kHz and a 1430 kHz. We need to make two T networks, one for each station. There are a few characteristics of a T network that can be used to our advantage here. A T network can also function as a low pass or high pass filter depending on the relationship between capacitance and inductance. In an inductive circuit the phase is advanced and in a capacitive circuit the phase is retarded. If we can make the phases of the two stations 180° opposing, this makes an excellent start to a filter network. Therefore, one station should be +90° and the other should be -90°.

So, on 980 kHz we want to match 50Ω to 74Ω with a +90° phase shift. Simple. Each leg of the T network needs to have the following value:

Z(leg)=√Z(antenna) x Z(transmitter) or Z=√(50 x 74) = √3700 = 60.8Ω

This is a highly simplified diagram that does not show the pass/reject filters employed between the ATU and the tower to properly combine both stations onto one antenna. That would be an extensive topic that I am not even sure I could adequately describe here:

Wdvh T Network Diagram

So each leg needs to have an impedance of 60.8Ω. The input leg is inductive, the ground leg is capacitive and the output leg is inductive. Remember, the output leg is already inductive by +j163. The inductive reactance needs to be canceled out, but some of it can be used in the T network. To make the output network match the rest of the T network, it will need 102.4Ω capacitive reactance (163-60.8=102.4Ω). To calculate these values, we use the L and C formulas which are 980 KHz = .98 mHz):

C = 1/(2π f (mHz)Xc) or 1/(6.28 x .98 x 60.8) or 0.00267 uf (ground leg, 60.8Ω)

C= 1/(2π f (mHz)Xc) or 1/(6.28 x .98 x 102.4) or 0.00159 uf (output leg, 102.4Ω)

and

L= Xl / (2π f(mhz) or 60.8 / (6.28 x .98) or 9.88 uH (input leg, 60.8Ω)

This combination should get us close to the Z 50Ω impedance that the transmitter is looking for.

The next frequency is 1430 kHz with a power of 10,000 watts. This frequency should be retarded by -90 degrees, so the input will be capacitive with in inductive leg to ground and a capacitive output. The tower measures 165Ω with -j105. Perfect!

Again, the current and voltage at the base of the tower on this frequency will be I=√(P/R) = 7.78 amps and E=√PR = 1,285 volts.

Wtmn T Network Diagram

Z= √(50×165) = √8250 = 90.82Ω

L = Xl / (2π f(mHz) = 90.82 / (6.28 x 1.43) = 10.11 uH (ground leg, 90.82Ω)

C= 1 / (2π f(mHz) Xc) = 1 / (6.28 x 1.43 x 90.82) = 0.00122 uf (input leg, 90.82Ω)

and

C= 1 / (2π f(mHz) Xc) = 1 / (6.28 x 1.43 x (-j105-90)) = 0.0074 uf (output leg, 75.8Ω)

Since the current and voltage for both stations are additive (with slight variations due to phasing on the two frequencies) the total current at the tower base will be 8.3 amps + 7.8 amps = 16.1 amps and the total voltage will be 608 volts + 1285 volts = 1,893 volts. Now you know why there is a fence around the bottom of the tower!

That is the theoretical part.  Using the OIB-1 and the generator, I tuned leg to ground to give the approximate valued noted above.  The inductive legs are easier to tune than the capacitive legs.  Since the value of each component is stamped on the name plate, I was able to estimate where the tap should go.  The capacitors are fixed, so they required some series/parallel connections to get the values close.

After all that, the transmitters are turned on and the system is measured under power.  Everything was pretty close, but a little bit of final tuning was required.

Once the transmitters were happy with the match, I did an full impedance sweep of both frequencies and recalculated the base currents for each station.  Then all of the harmonics and additive frequencies were checked to make sure that any spurious emissions were below the FCC required maximums.  That involved driving about 1 mile away and using a Potomac Instruments FIM-41.

The Frequencies measured were:

  • 530 kHz, lower intermod product
  • 1880 kHz, upper intermod product
  • 1960 kHz, 980 second harmonic
  • 2940 kHz, 980 third harmonic
  • 2860 kHz, 1430 second harmonic
  • 4290 kHz, 1430 third harmonic

And there you have it, that is how an AM transmitter is coupled to the base of a transmitting tower.

Tower down

You know it is going to be a bad day when:

a farmer mowing grass took a wrong turn on June 16, KFEQ AM lost a guy wire and eventually one of its four towers came toppling down

From Above Ground Level magazine.

Is hiring the farmer down the road to come and mow the AM field a smart thing to do?  It depends, I suppose, on whether or not your towers will be standing afterward.  Hopefully the guy had some insurance, if not then the station is basically screwed.  The article did not mention that, although it did state that “The station is wieghing it’s options,” Which does not sound good.

The good news is at least they were doing the maintenance.  Most AM stations these days don’t even bother to mow the fields.  Look at this picture:

Tall grass at an AM transmitter site.  Owner says don't cut it.

Tall grass at an AM transmitter site. Owner says don't cut it.

It is not that I don’t want the grass cut, I do.  However, I am not going to pay for it out of my own pocket, that is ridiculous.  So, it grows.