Found this interesting site
Meat Plow
May be of interest to some of the group RF nuts like me.
http://hawkins.pair.com/radio.html
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This is a test sig
Michael A. Terrell
Meat Plow wrote:
>
> May be of interest to some of the group RF nuts like me.
>
> http://hawkins.pair.com/radio.html
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.
Meat Plow
> Meat Plow wrote:
>>
>> May be of interest to some of the group RF nuts like me.
>>
>> http://hawkins.pair.com/radio.html
>
>
> I told you about that site a couple years ago.
Well shit, I don't memorize these things.
>
> Here is one about the different types of broadcast towers in use, in
> the US.
>
> http://www.fybush.com/
Did you watch the VOA videos or had you seen those before?
--
Live Fast, Die Young and Leave a Pretty Corpse
Michael A. Terrell
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.
Meat Plow
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.
Michael A. Terrell
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.
Meat Plow
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.
Michael A. Terrell
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. ;-)
Meat Plow
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.
Cydrome Leader
what sort of maintenance is required to keep those giant tube monster
walk-in transmitters running for decades?
Meat Plow
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.
Michael A. Terrell
Did you see the report about all three towers at WWVA collapsing in a
storm the other day?
Meat Plow
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.
Michael A. Terrell
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.
<http://www.middletownjournal.com/hp/content/oh/story/news/local/2008/08/04/mj080508mullinsobit.html>
for anone in the Cincinnati or Dayton area.