Found this interesting site

May be of interest to some of the group RF nuts like me.

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Reply to
Meat Plow
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I told you about that site a couple years ago.

Here is one about the different types of broadcast towers in use, in the US.

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Reply to
Michael A. Terrell

Well shit, I don't memorize these things.

Did you watch the VOA videos or had you seen those before?

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Reply to
Meat Plow

Yes, when I first found the site. I visited the VOA Bethany (Mason, Ohio) facility in the late '60s when it was being upgraded. The contractors were modernizing the controll rom, and had just finished installing the 10 new National Radio 50 KW transmitters. I also visted the WLW site the same day and got a good look at the 500KW transmitter.

Reply to
Michael A. Terrell

I going to try to arrange a tour of something that has that gear still in operation. Like a few Continentals some Marconis, some digital PSM/PWM gear. Listen to the hum and buzz, smell the rarefied air.

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Reply to
Meat Plow

It would be hard to match the WLW or an old VOA site with so many working transmitters.

The VOA site had ten new nationals, and all the original Crosley transmitters they were replacing. The Crosley were built before there was television, and they caused so much TVI that they were to be scrapped. The engineers said they had tried multiple modifications to fix them, but nothing they could do without a complete shutdown had helped.

The Crosley transmitters were cool, art deco styling with a beautiful fine grained green metal flake finish, and big glass windows. They were about 25 years old, but looked brand new. That's what a station can do, when they have a team of full time engineers.

That site could produce a total 1 million watts on any frequency from 2 to 30 MHz. They had a huge east west curtain antenna they used to hit Russia & Europe. The new National transmitters were continuous tuned, so all you had to do was dial in the desired frequency, and servo motors at each stage would tun the transmitter. I was kidding with one of the engineers if he had ever though about putting it on 27.185 MHz any yelling, "Hey 18 wheeler, there's a Smokey on your tail!" He turned pale as a sheet. Can you imagine thousands of semis slamming on their brakes, all over the country? He quickly changed the subject! :)

Modern transmitters look more like a server room than a transmitter. A solid state 5 KW AM transmitter isn't much more than a modulated switching power supply in a single 19" enclosed relay rack. The earlier Gate, Harris GE, RCA etc. were three or more racks covered with knobs & meters, along with a few buttons for LV & plate controls.

Reply to
Michael A. Terrell

I find the newer pulse width and pulse step digitals fascinating not really knowing much about them. One Marconi 500kw does pulse step modulation. Raises the efficiency from 70 to 90 percent. No need for a

150kw audio amp just to modulate. Takes more brains then I have to design a smart switching supply and amp to do that like the Marconi does. And hell that's 1975 technology to boot.
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Reply to
Meat Plow

Harris Broadcast had some white papers on their website a few years ago that described the operation of their solid state AM transmitters, but they had pulled them all the last time I looked. I have copies on one of a dozen small fat 32 hard drives. I haven't had the time to move all of the old files to one large NTFS drive yet. I just hope that they are still readable. Maybe that idiot 'General Failure' hasn't messed with the drive I need. ;-)

Reply to
Michael A. Terrell

I'm going to google the two methods of digital AM transmitters. There are some that still use a tube array final and some strictly solid state. One I was looking at had an 8 devices on a card, maybe TO-3PBL type case and each one put out 1Kw. These output modules in sync with the power supplies are modulated by switching them on and off. I guess that's PSM.

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Reply to
Meat Plow

what sort of maintenance is required to keep those giant tube monster walk-in transmitters running for decades?

Reply to
Cydrome Leader

On Fri, 06 Aug 2010 16:40:27 +0000, Cydrome Leader wrote:

Well it appears that maintaining proper cooling is number one. Some use forced air, other are water cooled. Both are watched closely. Some of the old RCA tubes are rebuilt because nobody makes them now. I'm sure time tested maintenance rituals are established and the intricacies thereof are unbeknown by me. Monitoring voltage, current levels and attending to monitored devices running out of spec seems plausible for ensuring proper operation. Upgrades to more efficient solid state stages in the string of stages from start to finish where applicable is another consideration. Considering the old Crosely stuff went into service in the late 20's one would assume a talented staff of techs who could make broken parts or find sources to rebuild would be a must. It's pretty complicated to keep the old stuff on the air in my estimation. This is why most old style facilities are retrofitting to solid state as it's easier to maintain, much more efficient and that means much less costly to operate when the electric bill comes in the mail. I'm sure that a 500kw site was spending several thousand dollars a month cranking out those watts. And the transmitters were designed to use half or part of the final output so any still running probably use a fraction of the designed output. Try the video link for the Voice of America tour. They explain a lot of the operation of both old and new equipment and how they propagate their signals.

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Reply to
Meat Plow

Did you see the report about all three towers at WWVA collapsing in a storm the other day?

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Reply to
Michael A. Terrell

No I didn't. That's a real FUBAR damn! I've actually been inside WWVA studio for the Saturday Jamboree back in the late 50's early 60's. My dad announced a commercial for one of the sponsors and had a friend who was a musician that performed in the studio.

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Reply to
Meat Plow

That is the second set of towers that have collapsed at WWVA.

I was in the WPFB studios and engineering area a number of times. They lost a tower to high winds or a tornado in the late '60s or early '70s. I can't find any reference online.

I also found that their long time country DJ, Moon Mullins passed away. He was a friend of my dad, when they were growing up.

for anone in the Cincinnati or Dayton area.

Reply to
Michael A. Terrell

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