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Brief Update

All is well in Engineering Radio Land, just very busy with typical projects. Nothing really note worthy, but there are some interesting things in the pipe line, which will be posted once those projects begin. Regarding myself, Hockey Season is in full swing.

Ruined shot on goal

My son (in blue) messing up somebody’s shot on goal. Good stuff.

I received an interesting question from occasional reader Gary over the weekend:

Have you ever heard of, or looked into, the “Max Headroom incident”?

Yes, I have heard of it, but never really thought about it that much. At that time, I was in California getting ready to ship out to Guam. I remember some brief news reports on it when it happened. After some reflection, I sent along this reply:

Good question. I have done a little bit of work at TV stations from time to time. In the mid to late 80’s, most television stations used 6 GHz analog microwave links between their studios and transmitters. These where unencrypted. Most often, these links used Microwave Associates gear, which had transmitter power output of about 3 watts into a rectangular wave guide. That was coupled, via elliptical wave guide into a 24 or 36 inch parabolic antenna. As you know, parabolic antennas have a main lobe and side lobes in their radiation pattern. The smaller the dish size, the broader the main lobe is and the further out the side lobes are. Since the Chicago studio to transmitter path was fairly short, I’d hazard a guess that they where using 24 inch antennas. In major markets, there was often a backup STL system on a different frequency (as the Wikipedia article indicates). Later on, most stations had a third backup via the cable company using either directly fed coax or fiber optic cable.

Since cutting into the transmission line of the microwave link at either side of the system would almost certainly fail, what I think happened is the perpetrators discovered (easy to do) the frequency of the 6 GHz link and over powered the normal signal at the receive antenna. This is possible if they used a much larger antenna and where located in either the main lobe or a side lobe of the receive antenna. If you recall, in the late 80’s C band satellite dishes where very popular. It would not be too difficult to repurpose one of these dishes for a 6 GHz antenna. Most C band dishes where 5-6 feet in diameter, which would give them much more gain than a 2 foot dish. They simply would have had to figure out a way to feed the dish with elliptical wave guide and adjust the focal length for 6 GHz. I’d bet there where dozens of C band dishes on Chicago roof tops.

Anyway, that is my theory.

I watched a few youtube clips of the event. The fact the video was noisy indicates some type of co-channel interference. I think there was no audio because they guessed the microwave audio subcarrier frequency wrong the first time. The second incident, there was audio. Whoever did to this had to have pretty good knowledge of television STL system. Wikipedia article here: https://en.wikipedia.org/wiki/Max_Headroom_broadcast_signal_intrusion

What do you guys think?

In other news, I have begun messing around with a few ideas on single ended tube audio amps and contemplating a DIY tapered transmission line speaker build. Actually, there is some pretty interesting software out there for speaker design which would be fun to play with.

I have also been messing about with room EQ Wizard, which I think I will do a separate post on.

That is all from here, hope that all of you are well.

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.

Mount Mansfield, highest point in Vermont

As alluded to in the previous post, I spent a fair amount of time at Mt. Mansfield last month. It is the highest point in the state of Vermont, topping out at 4,393 feet (1,339 M).  At the top, there is a large transmission facility that is home to WCAX-TV, WPTZ-TV, WVPS, WEZF, and several low power TV’s, NOAA weather radio, etc.  Next door, Vermont Public TV is housed in a separate building.  Here are a few pictures and descriptions.  First off all, Mount Mansfield is the home of Stowe Ski area.  They own the access road to the top of the mountain and are quite proud of it.  In the summer time, the toll for a car load of people is $26.00.

Mount Mansfield Toll Road gate

Mount Mansfield Toll Road gate

The transmitter building is below the actual peak.  This is one of the few transmitter sites that is manned 24/7, as such there is a working kitchen, bathroom, bunk rooms and so on.  I’d imagine it gets pretty deary up there in the wintertime, but perhaps not.

Mount Mansfield transmitter building

Mount Mansfield transmitter building

The transmitters are located along a long hallway.  WEZF and WVPS share a room, WCAX and WPTZ are in open bays as are the low power TVs.  NOAA weather radio and some other government transmitters are located over the garage.

WCAX digital TV transmitter

WCAX digital TV transmitter

All of the TV transmitters are new because of the recent conversion from analog to digital transmission.  WCAX is noted as channel three, which was their analog channel, they actually transmit on channel 22 with a power of 443 KW ERP.

WPTZ transmitter

WPTZ transmitter

Like WCAX, WPTZ was on channel five, it is now transmitting on channel 14 with 650 KW ERP.

The site is backed up by two 1.2 MW diesel generators, which can be paralleled with the commercial power grid, if needed, during peak demand times.  These generators also provide backup power for Stowe Ski area.   There is a 50 KW back up back up generator that runs all of the emergency transmitter cooling equipment if the two main backup generators fail.

Mount Mansfield generator

Mount Mansfield generator

All of this generating equipment requires a lot of fuel.

Transmitter building and fuel storage tanks

Transmitter building and fuel storage tanks

The TV and FM broadcast antennas are located just below the peak

Mount Mansfield TV and FM antennas

Mount Mansfield TV and FM antennas

I don’t recall which TV station belongs to which antenna. The FMs are combined into the four bay, three around panel antenna, this includes WVPS’s HD radio signal.

Mount Mansfield from the top looking west

Mount Mansfield from the top looking west

From the very top looking west into the aperture of the TV antennas.  I only stood there for as long as it took to get a good picture, then departed.  Off to the left of this view is the antenna for Vermont Public TV.

Mount Mansfield Vermont Public TV antenna

Mount Mansfield Vermont Public TV antenna

The transmission lines go down the hill on a large ice bridge.  An absolute necessity as the rime ice can sometimes accumulate several inches.

Mount Mansfield Ice Bridge

Mount Mansfield Ice Bridge

Tower base, which is the location of the highest RF concentration, according to the TV engineers.  I only lingered here to snap a few quick photos.

Mount Mansfield tower base

Mount Mansfield tower base

All of the STL antennas are mounted to the side of the transmitter building next to the living quarters.

Mount Mansfield STL antennas

Mount Mansfield STL antennas

On top of all that, as if that weren’t enough, there is the view.  I would also comment a bit on the weather.  In some cases, the site can be completely engulfed in a grey dull fog bank one minute, then the wind changes direction, the sun comes out and you see this:

Mount Mansfield morning

Mount Mansfield morning

I can think of worse things.

I regret that I didn’t have a better camera with me as several of the pertinent pictures came out blurry.  All of these pictures were taken with my cellphone camera, which works well, when it works.  It is also very convenient because it is almost always with me and I don’t have to remember to bring another gadget.  However, it this is going to be a semi-serious endeavor, I will have to take some of my earnings from these scribblings and buy a good camera.

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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