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The rotary phase maker

I alluded to this in an earlier post: Open Delta three phase service.  Some transmitter sites are fairly remote and three phase power is not available.  Occasionally, with lower powered radio stations, this is acceptable because those transmitters can be configured to run on single phase power.  However, almost any transmitter above five kilowatts or so will require three phase power.  This is the case at the WQBJ transmitter site in Palatine Bridge, NY.  The site is located in the middle of farm land and only has single phase service.  The nearest three phase service is several miles away and the utility company wants several hundred thousand dollars to upgrade the line.

WQBJ transmitter site electrical service

WQBJ transmitter site electrical service

The station is a class B FM with a six bay full wave spaced antenna.  Even so, the TPO is 17 KW, which makes some type of three phase service a requirement.

WQBJ six bay Shively 6810 antenna

WQBJ six bay Shively 6810 antenna

The main transmitter is a Broadcast Electronics FM30B, which is now 25 years old.

WQBJ main transmitter, Broadcast Electronics FM30B

WQBJ main transmitter, Broadcast Electronics FM30B

The backup transmitter is a CSI FM20T, which is almost forty years old.

WQBJ backup transmitter, CSI FM20T

WQBJ backup transmitter, CSI FM20T

Rather than do an open delta service, which is not desirable for several reasons, both transmitters have their own rotary phase makers.  From a reliability and redundancy standpoint, this is the right way to equip this site.  The rotary phase makers are essentially a motor generator combination which takes the split phase power and generates a third phase.

WQBJ phasemaster, backup three phase converter

WQBJ Phasemaster type T, backup three phase converter

Phasemaster parallel connection diagram

Phasemaster parallel connection diagram

The phasemaster is is a 40 KVA unit and is connected to the backup CSI transmitter

WQBJ Roto Phase, main three phase rotary converter

WQBJ ARCO Roto Phase, main three phase rotary converter

The Roto Phase unit for the main transmitter is actually two 40 KVA units connected in parallel through dry core isolation transformers.  Incidentally, the Roto Phase units need to have their bearings changed every ten years or so.  This requires the units be disconnected, placed up on their end.  To get the old bearing out, the housing has to be cooled with liquid CO2.  Both units are due for new bearings soon, which should be a pleasant job indeed.

Repairing the Nautel VS2.5 transmitter

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.

North Adams tower update

As promised in an earlier post, here is an update on the progress at the North Adams tower site for the restoration work on WUPE-FM and WNNI. For those unfamiliar, refer to this post: North Adams Tower Collapse.

A contractor installed a 70 foot wooden utility pole last week.  We ordered new Shively Versa2une FM antennas as replacements for the antennas destroyed when the tower fell last March.  These new antennas are field tunable, which is a nice feature.  The idea is that this pole will be used until the replacement tower is constructed, which is many months away.  After the new tower is up, I would like to keep the pole in place as a backup facility for both stations.

North Adams restoration work

North Adams restoration work

The bucket truck arrived but the driver had a bit of bad news; there is room for only one person in the bucket. The boss pipes up and says “Oh, that’s okay, Paul can go up and run the bucket”

WAT!

Are you sure this is a good idea?

Are you sure this is a good idea?

So anyway, it turns out running a bucket truck is not a huge deal; there is a joy stick of sorts that moves the booms around, up down, sideways, etc. Once you get the feel for it, it is pretty easy and three dimensional movement becomes second nature.  That being said, at 70 feet in the air, everything gets a little wobbly, so it is best not to jerk the controls around.

The antennas were mounted on a 2 inch pipe which was attached to the pole with 1/2 inch threaded rod. We left a little bit of pipe sticking up above the top of the pole to get the FM antennas as high a possible.

Mounting pole to tower

Mounting pole to tower

Mounting pole to tower

Mounting pole to tower

Some dude in a hang glider checking out the work

Some dude in a hang glider checking out the work

Getting photobombed by some guy in a hang glider is a new experience.  No day is exactly like another in this line of work.

WUPE and WNNI temporary antennas

WUPE-FM and WNNI temporary antennas

The antennas were tuned up once they were up on the pole. We did this with the network analyzer, which made the job very easy. WUPE-FM (top antenna) started using this antenna on Wednesday afternoon (5/7) with greatly increased power output.   This gets the station almost the same coverage area as they had before the tower collapse.  We tested WNNI (bottom antenna) and it all looked good. WNNI is still waiting for a temporary wireless internet feed for program delivery. Once that is established, we will have to do the intermod measurements one more time before they can go on the air.

Here are some pictures of the cleaned up site:

North Adams, fallen tower removed

North Adams, fallen tower removed

North Adams, fallen tower removed

North Adams, fallen tower removed

The temporary monopole being used by the cell providers:

North Adams temporary cell tower

North Adams temporary cell tower

Basically the pole is ballasted in place by those huge concrete blocks.

WEBE pictures

WEBE is fairly unique in that its antenna is mounted on the side of a 500 foot smoke stack. I took a few pictures last winter:

WEBE Main antenna

WEBE Main antenna

This is a close up of the Antenna:

WEBE main antenna, Shively 6 bay half wave spaced

WEBE main antenna, Shively 6 bay half wave spaced, ERP 50 KW

Here is an even closer view from a different angle:

WEBE main antenna, courtesy of NECRAT

WEBE main antenna, courtesy of NECRAT

From this angle, one can see the mounting brackets and the wire mesh reflector installed on the smoke stack.  From the first picture, one can see that the 400 MW PSEG coal fired power plant puts out a lot of combustion products when on line.  Combustion is an exothermic chemical reaction which looks like this:

Hydrocarbon Fuel + Oxidizer + Nitrogen  → Heat + CO2 + H2O + NOx

Included in this are any trace elements that are found naturally in the coal that is being burned.  These include things like Mercury, Nickel, Uranium, et cetera.  These trace elements can concentrate around the smoke stack because they fall out of the particulate quickly and these plants burn a lot of coal.  The above picture was taken on a very cold day, most of what is coming out of the smoke stack is steam.

The issue for the radio station is when the particulate matter accumulates on the antenna, effectively shorting it out.  The solution was to place the RADOMES around the elements and then constantly purge the RADOMES with nitrogen.  Thus, this liquid N2 tank is vital for the operation of the radio station:

Liquid Nitrogen Tank

Liquid Nitrogen Tank

Each element of the antenna has a small hole in the feed line. N2 is fed continuously into the transmission line at a pressure of about 1.5 inches water column which then purges the RADOMES keeping any combustion products out of the RADOMES.  The N2 tank needs to be changed out every 18-21 days and weights over 650 pounds when full.

North Adams Tower Collapse

High winds seem to be the culprit in the collapse of two towers in North Adams. According to the Motorola system technicians, it happened at about 12:30 am Sunday morning, which is when all their link loss alarms started going off.  The larger, self supporting tower broke from it’s mounting plate and tipped over into the smaller guyed tower next to it. Effected are WUPE-FM and W226AW (WFCR New England Public Radio) as well as NEPR new station WNNI which has not officially signed on.

Cellular service for ATT, Verizon and Sprint/NEXTEL were all knocked off line as well internet services and E911 dispatch.  Those services are coming back on line, with temporary modular cell units en route. News report from WWLP channel 22, Springfield, MA:

Here are some pictures:

North Adams Cell Tower

North Adams Cell Tower

WUPE-FM antenna on the ground

WUPE-FM antenna on the ground

WUPE-FM antenna

WUPE-FM antenna

WUPE-FM STL dish

WUPE-FM STL dish

Base of WUPE-FM (formerly WMNB) tower

Base of WUPE-FM (formerly WMNB) tower

WNNI antenna

WNNI antenna

WUPE-FM WNNI and W266AW transmitter building

WUPE-FM, WNNI, and W266AW transmitter building

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

North Adams Cell Tower

Tower base mounting plate, apparent failure point

Tower base mounting plate, apparent failure point

Tower base mounting plate

Tower base mounting plate

Tower Base Mounting Plate

Tower Base Mounting Plate

For pictures of the towers during happier times, refer to this post: Filtering for co-located FM transmitters.

Restoration work is underway with WUPE-FM expected to return to air at low power by Monday afternoon.

Update:

WUPE-FM was returned to air at low power by about 1pm on Monday 3/31.  We took an unused Shively 6812 antenna that was tuned to 94.1 MHz and retuned it to 100.1 by cutting 1/4 inch pieces from the end of the elements until it was on frequency.  It took a bit of doing, but with a network analyzer, we were able to get it to 1.2:1 SWR with symmetrical sidebands.  Running 600 watts, it covers the city of license and then some.

WUPE-FM temporary antenna

WUPE-FM temporary antenna, Shively 6812

The STL antenna is a survey antenna mounted on the side of the building. In this configuration, with the leaves off of the trees, we are getting about 250 uV signal, which is pretty good.

WUPE-FM temporary STL antenna

WUPE-FM temporary STL antenna

The site is now crawling with insurance investigators, cell site technicians, North Adams fire department, Berkshire County Sheriff’s officers, tower workers, etc.  After we finished this work, we cleared out to make more room for everybody else.  Estimated restore time for W266AW is Wednesday 4/2.

Planning for the replacement tower is already in progress, I’d expect it to happen fairly quickly. The next step for the broadcasters is to put up a 70 foot utility pole and get a full powered antenna for WUPE. This should happen in the next two weeks or so. That will serve as the temporary facility until the new tower is constructed.

Filtering for co-located FM transmitters

Well sited FM transmitter locations usually want some height above average terrain. This means either a tall tower or a high hill or mountain. Once a site is developed, co-location of other FM transmitters often happens because sites are expensive to develop. A second station can save money by using existing facilities.

For all those newly permitted LPFM stations; pay attention. If you are going to be co-located at an existing FM broadcast site, you may need to do this too.

Interference from intermodulation mixing products can develop when FM transmitting antennas are in close proximity.  This is especially true with solid state, broadband PA commonly used in today’s VHF FM transmitters.  Thus, when antennas are closely placed, external filtering is required.

WUPE FM transmitter site, North Adams, MA

WUPE FM transmitter site, North Adams, MA

This is the case with a current project in North Adams, Massachusetts.  New England Public Radio is placing WNNI on the air from the WUPE-FM site.  WNNI is using one of those new Harris (now GatesAir?) Flexiva transmitters and WUPE-FM uses a Crown FM-2000A.  The antennas are on separate towers, but the towers are in very close proximity, about 30 feet apart.  In order to avoid any possible problems, a Shively 2602-3A-FB 3 pole filter was installed on each station.  The filter is a band pass for the station installed on and a notch for the other station.

The primary concern here is mixing products between the two transmitters.  Both have broad band solid state amplifiers with low pass filters before the output connector.  There are three frequencies of interest;

  1. (F1 – F2) + F1 or (100.1 MHz – 98.9 MHz ) + 100.1 MHz = 101.3 MHz
  2. F2 – (F1 – F2) or 98.9 MHz – (100.1MHz  – 98.9MHz) = 97.3 MHz
  3. F2 + F1 or 100.1 MHz + 98.9 MHz = 199 MHz

That, plus harmonic measurements out to three or four harmonics of the fundamental frequency should be enough to demonstrate compliance with FCC out of band emissions standards.

Measurements on these frequencies must meet the emissions standards outlined in FCC 73.317 (d), which states:

Any emission appearing on a frequency removed from the carrier by more than 600 kHz must be attenuated at least 43 + 10 Log10 (Power, in watts) dB below the level of the unmodulated carrier, or 80 dB, whichever is the lesser attenuation.

It is also noted that this site has several cellular carriers and no doubt has or will have LTE at some point. We all know that rural LTE installations can create self induced problems, which are then conveniently blamed on the nearest broadcast station because, hey, why not?

To further complicate matters, New England Public Radio also has a translator, W266AW (101.1 MHz) on the same tower as WNNI.  The same measurements noted above will have to be preformed again for the translator.

WNNI FM transmitter and Shively filter

WNNI FM transmitter and Shively filter

WNNI equipment rack.  This is one of those new Harris (GatesAir?) Flexiva FM transmitters.

WUPE-FM Shively Filter

WUPE-FM Shively Filter

WUPE FM filter installation

wave spaced Shively antenna.  Antenna for W266AW below

WNNI 4 bay half wave spaced Shively antenna. Antenna for W266AW below

New WNNI antenna mounted on cell tower next to WUPE-FM tower. The W266AW translator antenna is directly below WNNI’s main antenna.

WUPE-FM 3 bay half wave spaced Shively antenna

WUPE-FM 3 bay half wave spaced Shively antenna

WUPE-FM antenna installed on the original broadcast tower.  I believe the tower dates from 1959 or so.

It is important to get this type of installation right the first time.  Creating interference all around or above the FM band is never a good strategy.  Going back to ask for more funds to make something right is also highly frowned upon.

The Shively Branched combiner

Did some work a while ago at a transmitter site that had three transmitter combined into one antenna.  The site uses a Shively branched combiner:

Shively Branched combiner

Shively Branched combiner

Each transmitter can be tested into a separate 20 KW dummy load:

Three inch coax switches

Three inch coax switches

Transmitter themselves are Nautel NV15s:

Nautel NV20 transmiters

Nautel NV15 transmiters

Except the one on the end, which is an older BE FM20A.

Series surge suppressor

Radio facilities, particularly mountain top transmitter sites, are prone to power transients. The causes can be varied, but most often, lightning is the culprit.  Long power transmission lines to the site are vulnerable to direct strikes and EMF induced spikes from nearby strikes.  Other issues, such as switching transients, load fluctuations, and malfunctioning equipment can lead “clear weather” outages.  Of course, the best way to deal with such things is prevention.

Power line surge suppressors have been around for quite some time.  They usually take the form of a MOV (Metal Oxide Varistor) connected between the hot leg and neutral or ground.  There are a few differences in designs, however.  Typically, most facilities employ a parallel surge suppressor.  That normally take to form of an enclosure hung next to the main power panel with a group of MOV modules in it.  The MOVs are feed from a circuit breaker in the panel.  Like this:

LEA parallel surge suppressor

LEA parallel or shunt surge suppressor

This is an LEA three phase 208 volt shunt surge suppression unit, which has MOVs between all phases to ground and each other.  That is connected in parallel to the electrical service with the circuit breaker disconnect.  These function well enough, provided there is a good bit of series inductance before the unit and also, preferably after.  The series inductance can come from many sources, including long secondary leads from the utility company transformer or electrical conductors enclosed in metal conduit, particularly rigid (verses EMT, or FMC) metal conduit.  The inductance adds a bit of resistance to the transient voltages, which come in higher than 50 or 60 Hz AC waveform.

A better method of transient protection is the Series Surge Suppressor.  These units are installed in line with the incoming service and include an inductor to add the required series resistance coupled with MOVs and capacitors.  Most series surge suppressor also filter out harmonics and RF by design, something desirable particularly at a transmitter site.  Series surge suppressors look like this:

LEA DYNA systems series surge protector

LEA DYNA systems series surge protector

This is a LEA three phase 240 volt unit.  As in the other example, all phases have MOVs to neutral and each other.   There are MOVs and capacitors on the line and load side of this unit (line side is the bottom of the inductor).  A basic schematic looks like this:

Series surge suppressor basic schematic

Series surge suppressor basic schematic

A few things to note; MOVs have a short circuit failure mode and must be fused to protect the incoming line from shorts to ground.  MOVs also deteriorate with age, the more they fire, the lower the breakdown voltage becomes.  Eventually, the will begin to conduct current at all times and heat up, thus they should also be thermally fused.  MOVs that are not properly protected from over current or over temperature conditions have the alarming capacity to explode and/or catch on fire.  From experience, this is something to be avoided.  Matched MOVs can be paralleled to increase current handling capacity.

The inductor is in the 100 µH range, which adds almost no inductive reactance at 60 Hz.  However, it becomes more resistive as the frequency goes up.  Most transients, especially lightning, happen at many times the 60 Hz fundamental frequency used in power distribution (50 Hz elsewhere unless airborne, then it may be 400 Hz).

Capacitors are in the 1-10 mF range and rated for 1 KV or greater as a safety factor.  The net effect of adding capacitance is to create a low pass filter.  Hypothetically speaking, of course, playing around with the capacitance values may net a better lowpass filter.  For example, at 100 uH and 5 mF, the cutoff frequency is 225 Hz, or below the fourth harmonic.  Care must be taken not to affect or distort the 60 Hz wave form or all sorts of bad things will happen, especially to switching power supplies.

These units also need have a bypass method installed.  If one of the MOV modules needs to be replaced, power to the unit has to be secured.  This can be done by connecting it to the AC mains before any generator transfer switch.  That way, the main power can be secured and the site can run on generator power while the maintenance on the surge suppression unit is taking place.

Restarting a Harris HT35 FM transmitter

This transmitter was retuned from 107.9 to 92.9 and put back into service. Retuning an HT35 transmitter is no small matter, there are 32 pages of retune instructions.  This unit is now in service as the main transmitter for WEZF, Burlington, VT.

The transmitter power output is 22,000 watts into a four bay, three around panel antenna, which gives it an ERP of 46,000 Watts at a height of 824 meters (2,703 feet) above average terrain. The tower is at the summit of Mt. Mansfield, which is 1,340 meters (4,395 feet) above sea level.

Mount Mansfield TV and FM antennas

Mount Mansfield TV and FM antennas

This is the Mt. Mansfield FM transmitter room. There are two TV stations in this building as well.

Final frames are of the WVPS Nautel NV-40 transmitter.

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

Axiom


A pessimist sees the glass as half empty. An optimist sees the glass as half full. The engineer sees the glass as twice the size it needs to be.

Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.
~1st amendment to the United States Constitution

Any society that would give up a little liberty to gain a little security will deserve neither and lose both.
~Benjamin Franklin

The individual has always had to struggle to keep from being overwhelmed by the tribe. To be your own man is hard business. If you try it, you will be lonely often, and sometimes frightened. But no price is too high to pay for the privilege of owning yourself.
~Rudyard Kipling

Everyone has the right to freedom of opinion and expression; this right includes the freedom to hold opinions without interference and to seek, receive and impart information and ideas through any media and regardless of frontiers
~Universal Declaration Of Human Rights, Article 19

...radio was discovered, and not invented, and that these frequencies and principles were always in existence long before man was aware of them. Therefore, no one owns them. They are there as free as sunlight, which is a higher frequency form of the same energy.
~Alan Weiner

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