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How do you make 100,000 watts?

Discussion in 'General Technical Questions and Answers' started by KB0TKZ, Aug 4, 2011.

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  1. KB0TKZ

    KB0TKZ Ham Member

    I'm curious as to how broadcast stations create their huge amounts of power. A local FM station, for example, mentions they broadcast with 100K watts. Do they use tubes? Many many tubes? Huge transistors?

    I'm also curious as to what kind of antennas they use? An omni-directional vertical?

    Anyone know?

    Thanks.
     
  2. KX8C

    KX8C XML Subscriber

    How do you make 100,000 watts? One watt at a time.
     
  3. KX8C

    KX8C XML Subscriber

    Lots of big parts able to take the amps, volts, and watts. The radio station a friend, who was chief engineer, ran used tube finals, and a grounding setup that had proven itself in practically every thunderstorm. And a vertical. Can't say I've seen a radio station using anything other than a vertical. But I could be wrong. My XYL tells me I'm wrong at least once an hour.
     
    Last edited: Aug 4, 2011
  4. W4AFB

    W4AFB Guest


    [​IMG]
     
  5. AF6LJ

    AF6LJ Ham Member

    Nice.
    To answer the OP's question some of that power comes from antenna gain.
    Your 100KW station was most likely stating effective radiated power,.
    With that said power levels in excess of 10 million watts CW are attainable using state of the art vacuum tubes and on lower frequencies 100KW can be achieved with transistors. Lots of them.
     
  6. WB2WIK

    WB2WIK Premium Subscriber

    The "100,000W" is an "effective radiated power" figure, likely 50,000W to a 3 dB gain antenna system (although there are many ways to do this, including 25kW to a 6 dB antenna system).

    FM broadcast stations are not vertically polarized. They're either horizontal, or a combination of horizontal and vertical.

    Tubes reigned supreme for these transmitters for most of history, but lately solid state transmitters are taking over...mostly because not so many folks manufacture tubes anymore. Just a couple of tubes can run this much power. With solid state stuff, it's usually an array of amplifier modules combined together. I'd expect that "some day soon," it will all be solid state.

    If you really want to see some "big" transmitters, check out what some shortwave broadcast stations use on HF. Some of those are well over 1 million Watts e.r.p., which could be 250kW output to a 6 dB gain system, or 100kW to a 10 dB gain system, etc. Many ways to do this, but in general those transmitters are real fun. I live very close to a 1.5 million Watt SW broadcaster here in southern CA. They use a 14.5 dB gain directional antenna, so the transmitter only had to run about 50kW output power or so, but it's real fun to go visit those sites and see what's going on. Usually, you can hold one end of a 40W fluoroescent lamp in your hand, and just hold it up in the air (connected to nothing but your hand) and it will light up just fine.
     
  7. KB1NXE

    KB1NXE Platinum Subscriber

    The solid state amp can be whole lot of lower wattage amp run into combiners. Think 50 or 100 X 1Kw amps into combiners. If you look at the schematic of modern SS amps (the IC-PW1 comes to mind as I have one) is really 4 X 250 watt amps into a hybrid combiner. That and water cooling make the amps handle the wattage.
     
  8. KB3LIX

    KB3LIX Ham Member

    I seem to remember that FM broadcasters were limited to 50kW erp,
    BUT stations that were at higher power BEFORE the 50kW limit was established
    were "grandfathered" at the higher power level.

    WAY...WAY...WAY back when in the '80's, I was chief engineer of WAMO-FM
    in Pittsburgh. It was one of the grandfathered stations as it was licensed for
    72kW ERP operation.

    It used just shy of 25kW from a Harris FM-25K transmitter to
    an 8 bay circular polarized antenna at 400' agl. (I installed the FM-25K)

    It used a single tetrode to generate the 25kW.
    I do not remember the tube type,
    but I THINK it was a 4CX20,000
    (I may very well be WRONG too)

    The driver stage was 4 solid state amplifier modules
    combined to achieve a 1kW drive for the final power amplifier.

    That was then, this is NOW...

    I'm sure the state of the art now uses solid state devices
    in transmitters up to the 25kW range.

    Do a google search on HARRIS-RF, they were a BIG manufacturer of
    high power broadcast equipment that IIRC was located in Quincy Illinois.
    At one time, Harris manufactured High Power SW broadcast transmitters
    in the 200-250 kW range. I suspect that they are still tube type since
    acheiving that kind of power would take a BUNCH of PA modules to gat
    that kind of power output.
     
  9. AF6LJ

    AF6LJ Ham Member

    Many years ago at Loral Corp. we built some 2.5KW S-Band (2.2-2.3GHZ)
    There were eight modules containing four five transistor PAs using TRW custom made transistors.
    Combiners in each module the eight modules ran into a "Magic-T". It was quite an amplifier for it's day two 6' racks bolted togather and four huge 28V power supplies to run it. This was air cooled and contained it's own wideband idolater, a waveguide switch and a waveguide dummy load.
    At the time I was impressed. :)
     
  10. KB3LIX

    KB3LIX Ham Member

    A quick search of Harris
    (I was curious just how much things have changed in the interviening years)
    lists solid state transmitters up to 40kW for FM broadcasting.

    It also lists tube type transmitters in dual configuration
    up to 80kW.
     
  11. WB2WIK

    WB2WIK Premium Subscriber

    Yeah, 40kW, 80kW, who cares? The antenna site really matters.

    Locally most of our FM BC xmtrs are up on Mt. Wilson at 6200' overlooking the city of L.A. which is all lower. They do fine. I can hear most of them driving through tunnels underground.;)

    I wonder how long "broadcast" services will actually survive? TV is now mostly cable or dish and only a very small user base actually receives directly broadcast service, which is very expensive to maintain. FM may not be far behind.

    Just "a guess," but I think during my lifetime, direct broadcast services could easily all disappear. They're expensive to run.
     
  12. AF6LJ

    AF6LJ Ham Member

    I think you are right Steve; I expect them to start disappointing in the next ten years.
    Actually that isn't so bad, they all will go to the Internet all the FM stations that is, most are already there.
    These days a smartphone is as good as a pocket transistor radio.
     
  13. KB3LIX

    KB3LIX Ham Member

    That is all well and good IF you have a site or sites with the elevation
    to cover an entire population center.
    Many cities are not so fortunate.
    They must make up for lack of height by using brute force.
    Antenna gain doesn't often cut it either.
    Due to the pattern compression in high gain antennas
    areas of weak signal are created often near the antenna.

    My market doesn't have mountains like Mt Wilson, it does have hills
    that are several hundred feet above average terrain but you have to go
    75 miles or more EAST of Pittsburgh to find mountains. The Alleghenies.
     
  14. NO2A

    NO2A Ham Member

    If any of you are familiar with WKBW 1520am in Buffalo,NY you know what a signal they have. Last winter I heard them during the day in central NJ. That`s a distance of about 450 miles! Talk about erp. Now if I could just use their antenna on 160m.........:p
     
  15. W1GUH

    W1GUH Ham Member

  16. AF6LJ

    AF6LJ Ham Member

    This looks like those "the filament water cooling must be on before applying filament voltage" kind of tubes.

    [​IMG]
     
  17. W0BTU

    W0BTU Ham Member

    I've always wanted to know what these tubes are.
    BIG transmitting tubesSM.jpg
    Found this photo on the Web somewhere.
     
  18. WA9SVD

    WA9SVD Ham Member

    AAAH, all too complicated. All you need is one watt, and a 50 dB gain antenna.:p
     
  19. KL7AJ

    KL7AJ Ham Member

    I worked with those vapor phase cooled triodes all the time. We got 14 years out of a 7490 in 24x7 broadcast service at 50kw!

    Cool collection....are those yours?
     
  20. W0BTU

    W0BTU Ham Member

    You mean something like this one?:

    observatory.jpg :)
     
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