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Friday Funnies: Frantic calls

Back when radio stations still had DJ’s, one would occasionally get the frantic “We off the air” call:

weve-tried-nothing

Nowadays, the unemotional monotone computer generated remote control voice says something like “Alarm, status channel 16, WXYZ silence…” or better still, the answering service.

In some ways, I miss the old days…

Troubleshooting an AM array

Today, there will be a quiz.

Recently, we had an AM antenna array go out of tolerance by a good margin.  This has been repaired, however, I though I’d post this information and see if anybody could identify the problem and the solution. Unfortunately, I don’t have a prizes to give away, however, you can show off your AM engineering prowess.

All of the information is pertinent:

  1. The station has two directional arrays (DA-2) using the same towers; the night time array is out of tolerance, the daytime array is not effected and is performing normally.
  2. There were no weather events connected with this event; no electrical storms, no major temperature changes, no rain events, no freezing or thawing, etc.
  3. The problem happened all at once, one day the array was performing normally, the next day it was not.
  4. Station management reports that some listeners were complaining that they could no longer hear the station.
  5. The ATU’s and phasor were inspected; all RF contactors were in the proper position, no damaged or burned finger stock, no evidence of damaged components (inductors or capacitors) was observed.  Several mouse nests were cleaned out of the ATU’s, however, this did not change the out of tolerance antenna readings.
  6. The towers are 1/4 wave (90 electrical degrees) tall.

Readings:

Tower Phase angle as licensed Current ratio as licensed Phase angle as read Current ratio as read
1 147.2 0.583 149.5 0.396
2 (reference) 0 1.00 0 1.00
3 -137 0.493 -125.8 0.798
4 107.5 0.481 92.7 0.355
5 -38.1 0.737 -60.2 0.623
6 -178.7 0.382 142.8 0.305

Licensed values for common point current is 13 amps, impedance is 50 ohms j0 and there is normally no reflected power on the transmitter.  On this day, the common point current readings were 8.9 amps, impedance 38.5 ohms +j5 the transmitter had 340 watts of reflected power.

This is the overall schematic of the phasor and ATU:

WDGJ overall RF schematic diagram

WGDJ overall RF schematic diagram, click for higher resolution

Aerial view of transmitter site, oriented north:

WGDJ aerial view showing towers as identified in schematic diagram

WGDJ aerial view showing towers as identified in schematic diagram

So, where would you begin?  Ask questions in the comments section.

The Shukhov Tower

A very interesting bit of broadcasting history in Moscow may disappear forever.  Designed and built by Vladimir Grigoryevich Shukhov, the Shukhov Tower was completed in 1922.  Since that time it has served as a AM broadcasting and later and FM broadcasting tower.  In the picture, one can see what looks like a massive FM panel antenna at the top.  According to this website: www.shukhov.org, the tower is in very poor shape and is slated to be demolished.

The tower itself is described as 160 Meters (525 feet) tall, hyperboloid steel lattice structure. The design is unique in that it is very strong, yet uses approximately 60-70 percent less steel than a comparable four legged structure like the Eiffel tower.  An amazing feat of engineering for its day, when everything was calculated and drawn by hand.

Shukhov Tower, Moscow, FSR

Shukhov Tower, Moscow, FSR.

The antenna is a little hard to discern, however, it looks like a horizontally polarized six or eight around 4 bay FM antenna. Could also be low band VHF TV.

Shukhov Tower antenna

Shukhov Tower antenna. Courtesy Wikipedia

Unfortunately, time is running out and little or nothing is being done to protect the steel structure from the elements. The last paint job was more than twenty years ago. The land it currently occupies has some value, and there is talk of putting up a high rise development in its place.

Article from the New York Times; An engineering landmark faces demolition in Moscow.

There are lots of videos on youtube and pictures from the wikipedia article.  It is an interesting bit of history, if it can be saved it will be a very close run thing.

WMHT’s former analog transmitter

During the digital TV conversion in the US, all broadcast television stations installed new transmitting equipment and antennas.  Most stations ended up on a different frequency than their original analog channel.  In Albany, New York, all of the TV stations moved to a common transmitter site and installed their antennas on a single tower.

home of WRGB, WTEN, WNYT, WXXA, WMHT, and WCWN

Albany DTV tower, home of WRGB, WTEN, WNYT, WXXA, WMHT, and WCWN

For more on the Albany DTV site, check out the NECRAT page: www.necrat.us/albdtv.html

So, what happened to the old Analog TV sites in Albany?

For the most part, after the analog turn off on June 12, 2009, the sites have sat empty.  Such is the case with the former WMHT site.

Sign outside of former WMHT transmitter building

Sign outside of former WMHT transmitter building

This old sign about sums up the end of analog television.

Former WMHT Comark analog transmitter

Former WMHT Comark analog transmitter

Former WMHT analog transmitter wide shot

Former WMHT analog transmitter wide shot

Former WMHT operator position

Former WMHT operator position

The former transmitter operator desk. Maintenance log is still open. From the looks of things, they opened the circuit breakers and walked away. Everything remains intact from the antenna to the klystrons and exciters. It does appear that the coolant has been drained from the system. Other than that, it seems like the whole thing could be restarted with minimal effort.

Former WMHT Onan DFN 350 backup generator

Former WMHT Onan DFN 350 backup generator

There were two Onan DFN 350 backup generators. With a TV transmitters, it is vitally important to run the cooling system after shutdown. The idea here is that both generators in parallel could run the whole station, if one generator failed, then the cooling system would still run and cool the klystrons.

Former WMHT site kitchen

Former WMHT site kitchen

Former WMHT tower, wave guide and WVCR antenna

Former WMHT tower, wave guide and WVCR antenna

The former WMHT tower, which currently holds the WVCR-FM, WXL-34 (NOAA weather radio), and W44CT-D (Three Angles Broadcasting) Low power TV transmitter.

Current site occupants; WVCR-FM and W44CT-D

Current site occupants; WVCR-FM and W44CT-D

These equipment racks and the NOAA weather radio transmitter in the other room are the only active equipment at this site.

WMHT-TV Chanel 17 (488-494 MHz) signed on 1962 from this site.  The Comark transmitter was installed in 1984.  The station’s analog ERP was 2000 KW visual, 200 KW aural.

It is an interesting site.

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.

A brief Pictoral History of early micro-computers

I enjoy history, perhaps more so than others.  My first computer was an Apple IIC, purchased in 1985.  It had a single 5 1/2 inch floppy drive, no hard drive, and a wee little monochrome monitor.  Basically, it was a glorified word processor until I figured out how to connect it to my Amateur Radio transceiver.  Here is a picture of my radio room, circa 1988 on Guam:

Radio Room, KH2R Guam Circa 1988

Radio Room, KH2R Guam Circa 1988

Finding more things to do with it became a hobby of sorts.  After a while, I realized that what I wanted was what we termed an “IBM clone,” what is know as a PC today.

When I came across this blog post; History of Computers, I found it interesting and thought I’d share.

Enjoy!

Those Shortwave Sites

How is our Alaska doing?

How is our Alaska doing?

It is a joke in circulating in Russia at the moment.  Kind of funny when you think about it.

In light of the developing situation in Eastern Europe, it may be wise to retain some of those HF broadcasting (AKA Shortwave) sites.  It may be too late for Canada, however, the US government still has a few high powered HF sites that they may want to hold onto for a while.  There are several ways that shortwave broadcasting can be beneficial.

  • Like all radio broadcasting, quality content is needed to attract listeners. Most of what is available on shortwave is religious or transparent government propaganda. There are exceptions to this, but they are rare. Introduce quality programming, and shortwave listenership will increase.
  • DRM 30 (Digital Radio Mondial) is still in its experimental phase.  It has been demonstrated to work reasonably well on HF.  Several digital data formats are successfully being used on HF; HFDL, ALE, STANAG 5066, PACTOR and others.  DRM 30 has an advantage that H.264 video can also be transmitted.
  • The VOA has been experimenting with images transmitted via MFSK, AKA the “VOA Radiogram.”
  • HF is always susceptible to changing propagation.  However, it can be reliable enough, especially when frequency diversity is employed, to overcome these issues when no other method of communication is available.
  • DRM and MFSK can be decoded using a simple shortwave radio and a computer sound card.  A DRM CODEC is required, but those are readily available for download.
  • Analog shortwave broadcasting using AM is still viable.  AM has the advantage of being extremely simple to receive and demodulate.  Simple receiver kits can be built and run on 9 volt a battery.
  • While the Soviet Union had an extensive jamming network, those sites have long since been non-functional.  Most countries have discontinued the practice of jamming with the exception of China, North Korea, Cuba and perhaps some countries in the middle east (the usual suspects).

Sample of DRM reception via shortwave:

If the internet is censored or somehow becomes unavailable in that part of the world,  shortwave may be the only method to convey an alternate point of view.

Hopefully, things will settle down and return to at least a civil discourse.  However, it never hurts to have a plan.

Decomissioning a NEXTEL site

Remember when “NEXTEL (b-b-b-beep), how business gets done…” Well, not anymore. NEXTEL was purchased by Sprint in 2005 and their product lines were combined.  Thus, all of these old NEXTEL sites have become redundant and switched off.  This particular site was co-located with one of our FM radio clients, which required a power reduction while the old equipment was removed from the tower.  I took the time to grab a few pictures of the process:

Former NEXTEL communications equipment room

Former NEXTEL communications equipment room

All of the equipment was removed from the equipment shelter. This site has been switched off since June of 2013 and everything in it is destined for the scrap yard.  This equipment worked on the 800 MHz band, which has been re-purposed for Public Safety and Critical Infrastructure, e.g. government users.  These racks and radios look like they were expensive:

NEXTEL equipment racks and radios

NEXTEL equipment racks and radios

Speaking of expensive, this site had over 4,500 feet (1,370 meters) of 1 5/8 inch foam coax, which was cut up and scrapped.  At today’s prices, that cost $13.25 per foot.

Scrapped transmission line

Scrapped transmission line

The tower was rigged:

Rigging tower to remove antennas

Rigging tower to remove antennas

Each of the three panel sector mounts were removed and lowered to the ground.

Dropping cellular panel antennas

Dropping cellular panel antennas

The NEXTEL antennas were mounted at the 260 foot (80 meter) level of a 395 foot (120 meter) tower. It took some time to remove all of the antennas and equipment from the tower.

Cellular panel antenna array being removed from a tower

Cellular panel antenna array being removed from a tower

I looked on the Sprint website and could not determine if they still offer a push to talk service option (direct talk).  With all of the communications options available today, I do not expect there would be much call for it.

For old times sake, here is an old NEXTEL commercial from many years ago:

They did have a good marketing department…

Engineer Killer

That was the title of the email with this photo attached:

Disabled high voltage shorting bar, Collins 820D-2

Disabled high voltage shorting bar, Collins 820D-2 AM transmitter.  Courtesy Pete Partinio

Seems about right.

For many, many reasons, this is a bad thing to do.  First of all, that shorting bar is the last point of discharge for the high voltage power supply.  When all else fails, this is designed to route the 3,500 volt plate supply safely to ground.  Having a stray 3,500 volts floating around inside of a transmitter is never a good idea.  Fortunately, it was spotted and removed before anything bad happened.

Secondly, it looks like somebody used a 12 VDC cigarette lighter plug as an insulating device.  Wow, did they get lucky.  This could have started a fire.

As to exactly why it was there in the first place, I cannot rightly say.

And this is why only properly trained people should be working on transmitter, especially tube type transmitters.