Category Archives: Off Topic

Road Trip, Part II; The New Tower

Off Topic warning: This has absolutely nothing to do with fixing up my house. I wrote about my road trip to Gainesville, Florida a while back. This is the follow up trip, only this time it involves flying to Gainesville instead of driving.

The replacement tower has been put up, the new unipole antenna has been installed and now it is time to match the transmitters to the new 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. More challenging, and thus much more fun. So, here goes…

There are two radio stations combined onto the same tower, this makes the problem extra special as filter networks need to be installed to make sure that each frequency does not get back into the other station’s transmitter.

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, we can figure out almost anything we need to know 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 (gound 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!

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

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Bottling the bitter

Yesterday, I awoke and decided it was time to check the specific gravity of my homebrewed bitter.  It was 1.011 so bottling time was at hand.  Using the Alcohol by Volume formula:

OG-FG/0.00738+(carbonation) 0.5 = % alcohol

Where:
OG-Original Gravity
FG- Final Gravity

Therefore, 1.038-1.011=.027 then .027/0.00738=3.7 then 3.7+0.5=4.19% alcohol. Slightly high for a bitter, which usually runs ~3.5-4% ABV.  I probably used just a little too much brewing sugar.  Still, I don’t think it will be ruined or anything…

As always, I tasted the specific gravity sample from the fermenter to see if there were any untoward flavors or odors.  It tasted pretty good.  I can see the hoppy bitter taste is there and the rest of the brew will mature over the next month or two in the nice cool dark basement.

coopers homebrewed bitter aging in recycled bottles

coopers homebrewed bitter aging in recycled bottles

About the bottles themselves, they are dark amber with a non-twist off top. I had collected them used over the last 6 months or so.  I was sure to use all the same type and size of bottle (Sierra Nevada IPA) so I didn’t have to change the bottle capper around during the middle of a bottling run.  I soaked and scrubbed each bottle using a bottle brush, then placed them in a tub of sanitizing fluid (6 gallons of water to 3/4 cup ordinary household bleach) and let them sit for a week.  Yesterday morning, just before I was ready to fill, I rinsed them all out with cooled boiled water.  It has been said many many times that when making beer, it is important to be as clean as possible.

The Super Agata bottle capper works really well.  I used oxygen barrier caps, they were only a little more expensive than the regular caps, so I figured why not.  I filled each bottle almost to the top with the bottle filling tube.  Once I removed the bottle, the beer was down to the correct level and I put the priming sugar in.  I waited about 30 seconds to cap each bottle so the carbon dioxide that bubbled up after adding the priming sugar would force all the oxygen out of the bottle.  I used 64 12 oz bottles and 2 24 oz bottles, although the last bottle may be a little questionable.

I have to say, the Coopers Microbrew kits are an excellent way to get started as a homebrewer.  I am going to do one more coopers kit brew, a stout.  After that, I feel that I have learned just enough of the basics by brewing a few no boil wort batches that l can branch out and do some extract brewing with different recipes.  Perhaps a good oatmeal stout for the cold winter months, we shall see.

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Cold War Relic: AT&T microwave relay 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.

disused att microwave relay site, Kingston, NY

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.

disused att microwave site building, Kinston, NY

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 5 to 6 gHz frequency range.

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.

att microwave relay site blast baffles

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.

att microwave site blast door actuator panel

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. This microwave relay site would not have withstood a direct hit from a nuclear warhead, especially the higher yield warheads that came later on.

att microwave site water chillers

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.

att microwave site stairs to 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.

att microwave relay site high voltage switch gear

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.

att microwave relay site first floor inside

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 to the north, 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. These copper wires would have DS-1 and DS-3 circuits routing long distance calls from local telephone company offices in Kingston and Poughkeepsie to the microwave site so they could be transmitted across country. A DS-1 circuit (Also known as a T-1) could handle 24 simultaneous calls, a DS-3 could handle 672 simultaneous phone calls. All of this call routing was done automatically by the 1970’s.

I don’t know if there are any photo’s of the inside of the building when it was in operation, as AT&T took security very seriously. Any photos of communications sites and equipment would have been considered contrary to national security interests.

All in all, this was a serious building, no expense was spared in the construction and equipment outfitting. 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. Some people I have talked to “Old timers” as they are known in the local phone company, say that the government subsidized the construction of this building. I am not sure it that is true or not, but it is not a stretch of the imagination to think it is.

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Autumn

I went for a drive this morning to run a few errands.  I took the camera along.  On my way home, I took the back way so I could look at the stream after yesterday’s rains.  This is the Stony Kill (Kill means Creek in the Dutch language).

stony kill

The rains, they have come and refilled our creeks and rivers.  It has been a warm autumn so far, we are going to have our first frost tonight, which is about two weeks later than normal.

forest

The trees behind our house.  Lots of mature Sugar Maples, a few Oaks and even an  Elm tree that survived Dutch Elm disease.

sugar maple tree

Late color, most of the leaves are gone now, this Sugar Maple shows off across the street.

small farm in upstate ny

A working farm in the bottom lands around the Rondout Creek.  This is a typical small farm in the area.

old bridge over the stony kill

Old bridge to nowhere across the Stony Kill.  Used to be part of a farm that has long since been abandoned, the land returning to forest.

country lane upstate ny

A country lane.

abandoned farm upstate ny

Fallow farm, the buildings are slowly being reclaimed by nature.  It starts small, a little moss on the roof that traps moisture so more moss and lichens can grow.  This traps more moisture and the insects find a home.  Decay follows the insects and pretty soon there is a hole in the roof.  The building slowly falls in on itself and in a few years, little trace will remain accept perhaps the foundation.  Eventually everything returns to the earth from which it came.

catskill mountains

Catskill mountains in the distance.

old cemetery upstate ny

The long slumber, graves in an old cemetery covered with a blanket of leaves waiting for the first snow fall.

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A creapy thing happened last night.

It was very late, or early depending on your perspective. My wife and I had turned out the light and said good night to each other some time ago. As I lay in bed drifting between half awake and half asleep I noise entered into my train of consciousness.

At first it was incorporated into the dream world that was forming, but then it seemed to pull me back toward being awake. So I lay there listening for a few moments. I thought it might be one of the kids, but they seemed to be sleeping just fine. I did not hear anything else so I began drifting again, welcome sleep coming on after a long day. Then the noise happened again and I snapped back to consciousness fully alert. Whatever it was was outside.

Now, we have all heard tales of houses being built on old Indian Burial grounds, or some other misfortune that happened to an unsuspecting home owner. These events almost always have a bad outcome. I will tell you that there are some areas around here, especially when the leaves are off the trees, as they are now, which take on a slightly sinister character. Old gnarly trees appear like giants waving their arms in the wind. Hump backed old mountains lay low against a troubled sky. The wind howls, the rain can thrash and in a flash of lightning it can appear that a figure is standing outside the window looking forlornly off to the west, watching the storm approach.

At least that is what can happen.

I sat up in bed and peered out of the bedroom window into the back yard. On this night, it was fairly calm outside, a slight breeze with half moon and all seemed normal. So, what had I heard? My wife was now sitting up looking out of the window too. “Did you hear that?” I said in a low voice.

“Yes” was the reply.

We looked out of the south window toward the side yard when I saw it. A very large man appeared to be standing under the pear tree about twenty five feet away. He was thrashing the lower branches violently with both hands. The branches were swishing back and forth and every once in a while he grunted with the effort. That is what I heard! That is what woke me up! I was transfixed, as was my wife. I said “What the…”

The man apparently heard me because he stopped, then got down on all fours. But then, he took on a completely different shape, in fact, he looked almost like… a bear! My wife and I said in unison “It’s a bear!” There was no quiet voice used this time and the bear definitely heard us. He or she took off across the yard and into the woods. Let me tell you, a bear can run pretty fast!

The next day I went outside to find our garbage can had been tipped over and gone through. The area under the pear tree where the bear had been standing on it’s hind legs was about 7 feet tall. Not only was it a bear, but it was a big bear. I can see how someone see a bear standing on its hind legs in low light conditions could mistake it for something else, like a Sasquatch or something.

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