Crosley was a famous name in radio for more than one reason. The National VOA Museum of Broadcasting has a video telling [Powel Crosley Jr.’s] story, and the story behind the 500 kW WLW transmitter. WLW was an AM broadcast station often called the nation’s channel since its signal covered most of the United States. The first Crosley station was identified at 8CR, running 20 watts from [Crosley’s] living room. Quite a modest start! By 1922, he had moved to his family business location along with 500 watts of output. Over the years, WLW got more powerful until it was finally a 500 kW giant.
Along the way, WLW had several firsts, including the first remote transmitter. The 50 kW transmitters are huge. The video also covers how Crosley made inexpensive radios including crystal radios and inexpensive tube sets.
From the technical point of view, these old tubes with 100,000-watt plate dissipation are truly amazing. There were several of them in the 50 kW transmitters. It is hard to imagine that the output would rise by a factor of 10 over the years. The transmitter used a DC generator that produced 4,000 amperes just for the tube filaments!
In a way, it was vertical marketing — produce programming and match it with inexpensive receivers to listen to the programming. This video is a great look back at a grand radio station. We’ve seen a tour of WLW before, though. When AM was king, there was a lot of work on making sure stations didn’t interfere with each other and that clear channels could cover most of the country.
The one below is also watch worthy.
It’s a 200kW mechanical transmitter from a museum ( built in 1924 or there abouts) that gets started up and operated.
SAQ Grimeton Transmission on July 4th 11:00 CET (09.00 UTC)
https://www.youtube.com/watch?v=lbvsHUBM18Y
That’s the one that is basically a big 17kHz alternator, isn’t it? Blew my mind as a kid when I realized, if you can generate 50 or 60Hz, what says you couldn’t build a machine to produce much higher frequencies, and that that was the only way to do it before thermionics were worked out. Sure, you can spin it faster, but the trick is More Poles.
(And yes, Mr Tesla devised a means of producing even higher frequencies back in those same days, but that method had a bit of a bandwidth problem)
Yes, see the description under the youtube video. It has 488 poles and runs at 2115rpm >>> 488*2115/60 = 17202Hz
I always get confused a bit by “poles” versus “pole pairs”. there are two polarity changes in a single sine, so I assume it should be pole pairs, but in the video they mention a “disc with 488 holes”. There is not much technical detail in the video. It’s mostly made to impress a wide range of public visitors.
Also, with 200kW, you can’t make the poles too small, so the diameter of the generator already has to be quite big. The energy stored in that flywheel must be quite big. You probably can’t go much further without the thing ripping itself apart.
Apparently such transmitters were quite common back then. There was no other technology available to make a transmitter at that power level, and transmitters of that type have been used on ships in that era.
Went on a visit to Grimeton last year, very interesting place.
Interesting to see the banks of water cooled resistors (3 I think, about the size of a UK red phone box but maybe 2/3 the height) used to dump the load when the transmitter was idle.
Then there was the story when they upgraded their generator hardware (in the 60s?) they got a call from the electricity company to see if there was a problem as their power usage had significantly dropped.
Can somebody wrap up for us non radio nerds why this is so special?
Because… 500kW?!? :)
Most modern ham radios operate at about 100W max. Licensing in US limits you to usually 1.5kW for most bands.
The nonprofit college radio station I worked at in college (FM) puts out 713W.
Wolfman Jack claimed “50 thousand watts of power” or something.
So 500kW is a ridiculously high amount of power and, especially given the means of generating that at the time and even today, is technologically and absolute basis interesting.
Thanks for your insinds and how you explain it. Its makes it a lot easier to understand.
A boat-load of focused energy, blasted into the ether for others to receive.
That would be the special part of a hundred year old relic, still capable of doing what it was designed to do.
Your desktop uses around a kw if you have a nice PC and game with it. Imagine cranking out most of that energy as RF instead of heat. Eventually it all has to get absorbed and converted to heat. If you don’t cook standing next to it, it has to cover an insane range.
With that amount of power, you could reach most of the United States with one tower. 50KW stations now (clear channels) have a large dead area past the ground wave’s reach (100 miles-500 or so) where you hear only static; but at night the signal reflects off an ionosphere layer and you get a big ring of reception which can add millions of listeners. But it’s subject to fading, storms, interference… and the slow fading of AM radio, replaced by FM stations all over. Nowadays the same superpower coverage can be had with satellite radio.
Not a radio nerd either but I do know enough that even just a 50,000 W transmitter is sufficient to broadcast to an entire medium sized country. 500,000 W is an order of magnitude greater. It feels like it would be more than enough to cover a large country like the USA or more.
Is there a trick to these 500kW like there is in speaker sets that often claim to be many hundreds of watts but really aren’t? How much electrical power does this transceiver really need? Is it really half a nuclear power plant?
I meant to write Transmitter
Article says 4000 Amp just for tube filaments so…. tons of current.
This isn’t exaggeration like the marketing BS. The FCC or which ever governing body would certainly take a dim view of falsified numbers
The FCC was actually formed in response to this station.
Considering this was output power, and how low efficiency of amplification was then, I am GUESSING, that the 50%rule would have been about the best at time. So, I’d again guestimate a rough 1million watts input power. No trickery, just raw power and simple physics. That thing was a whole warehouse heater!
That makes my “LITTLE” Dentron Clipperton L 2kW input amplifier look like a toy, and I’ll be honest, I’m afraid of the inside of my amplifier.
Was it 4000A at 28V for filament supplies, that’s about 100kW right there, and they used the older 50kW transmitter just to drive the signal into the 500kW amp. And then all the pumps for the water cooling, did they say 75kW just to move that water around? Probably goofed those numbers, didn’t take notes during the video, but there definitely was a cooling pond with 16 big sprayers to dissipate all the heat.
There are 2 ways of specifying power: actual transmitter power and effective radiated power. (in broadcasting referenced to the power produced with watts into a dipole, rather than isotropic radiator)
Example: 5 megawatt TV stations typically had 120 KW transmitters or smaler with antennas that have gain, primarily in elevation sometimes azimuth as well. Generally colinear stacked dipoles or slots sometimes with reflectors.
A 50 KW Wolfman Jack station probably had multiple antennas in a directional array with antenna gain.
Most early stations were omnidirectional and the transmitters were pretty close to the effective radiated power.
So my read on this is they’re referring to transmitter power in this case.
At one time transmitter power was rated by the DC that fed the output stage rather than the RF coming out of the transmitter, so that’s yet another way of specifying power.
Your average nuke plant puts out a gigawatt of power. Note that 746 watts is a horsepower, so compare that to the output of some of today’s electric cars. So a half megawatt is not such a big deal. I worked in a testing lab that had a 390KV at 1 amp power supply. and it was kind of the same size stuff as the WLW transmitter.
At AM radio frequencies, you don’t get to build high gain antennas, and if you only have one vertical mast, you’re lucky to get a couple dB gain. Fortunately, you don’t radiate anything upwards, and have a ground plane which mirrors the above ground and below ground fields … I just confused you, so just put a mirror on a table, and a table light on it. You see twice the light from the lamp that you would if the table was black. Wires were buried in the ground radially from the tower to make this mirror, and some stations were built in salt marshes to have the same effect.
“I just confused you, so just put a mirror on a table, and a table light on it. You see twice the light from the lamp that you would if the table was black.”
(Sportscaster)
“He stumbles, he fumbles, he recovers, he scores!”
Typical nukes running today about about 1000 MW, 2000 times 500kW
Transmitters like these are usually classified by transmitter carrier output power. Traditionally AM broadcast transmitters operate in double sideband which means that on “full volume” (100% modulation depth) the carrier power is 500kw and each sideband is 6dB below this, or 125kw each so the actual net output power is 750kw.
The efficiency of the transmitter typically varies across the different frequencies it can operate on, and according to the age/technology of the transmitter used. SW transmitters from 30+ years ago were ~70% efficient meaning on 100% mod depth the input power would be around 1.1Mw
You’re gonna want a good SWR.
Here’s a really informative video of how WLW was constructed.
https://www.youtube.com/watch?v=CbHjcwIoTiY&ab_channel=K7AGE
European stations dwarfed WLW, Radio Luxembourg 1440 kHz had 1,300 kW and France Inter 162 kHz had 2,000 kW.
There are 2 mw stations still. Radio Riyad and others. The blanket me here in the Caribbean.
–Shane
WP2ASS
I can only imagine that electricity bills were a joy.
Is this something we can replicate today with an USB SDR dongle? :-)
Damn, now *that* was engineering! The sheer scale of everything is amazing; I mean, 4.5 *Henry* transformers rated at 135KVA (or was it 185KVA), across a 30Hz-10KHz bandwidth? The size of the rectifier tubes, 100 kW just to drive the filaments? The whole thing is incredible. It’s also a cautionary tale about the impact of politics on business: The thing had a what, 5 year life at max daytime power just because a politician had a buddy in the same business.
I love pieces like this, would love to see more of them.
(Of course, all this is completely dwarfed by the engineering in modern electrical power transmission. I’d love to see an article about 500KV DC transmission lines, and the step-up/step-down circuitry.)