December 2012
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The Continental D323C medium wave transmitter

I found a 1981 Continental Electronics equipment catalog at an old transmitter site. These finds are great if one is interested in history and looking at the way things used to be done.  This particular transmitter is a 2,000 KW (2,000,000 watt) medium wave unit:

Continental Electronics D323C, Circa 1981

Continental Electronics D323C, Circa 1981

I believe most units like this were destined for use by government broadcasters either the middle east or western Europe.  I know there were several 1,000 KW medium wave stations in West Germany at one time.   The Continental transmitter is basically two 1,000 KW units (323C) combined.  They used a modified version of Doherty modulation, that is called “Screen and Impedance,” which accurately describes how it works.  More information from the Continental Catalog can be found here: Continental D323C.  The tubes (or valves depending where you are located) used in the D323C were 4CW25000A tetrodes as modulators and IPA the final was a pair of X2159, which is an impressive tube.

EIMAC X-2159 water cooled power tetrode

EIMAC X-2159 water cooled power tetrode

The tube sat anode up.  The filament, grid and screen connections are underneath.  Cooling water was pumped through the two connections on the top at about 130 gallons per minute depending on the plate dissipation.  With a 30° C rise, that equals about 96,000 BTU per minute.  The D323C had a dissipation of 400,000 watts for the carrier tube and 240,000 watts for the peak tube (640 KW total) under 100% modulation.  That equals about 2 million BTU per hour.  Notice the lifting hook, this tube weight in at 175 pounds.  Tube date sheet here.

Continental no longer makes medium wave transmitters, their closest high powered broadcast product now is the 418/419 and 420 HF (shortwave) transmitters.  The 420D does a wimpy 500 KW using a solid state modulator section.

I remember in the early 1990’s when I was at the Harris plant in Quincy, they were working on a 1,000 KW solid state DX series AM transmitter for Saudi Arabia.  It had to be liquid cooled, which added another layer of complexity to an already complex system.

I don’t know if there is much call for 2 MW medium wave transmitters anymore as there are more efficient ways to reach remote populations and I can’t even imagine what the electric bill would be like.

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6 comments to The Continental D323C medium wave transmitter

  • Dewey Jacks

    This is really neat stuff! As a ham radio operator,I LOVE reading about this kind of stuff and seeing the photos. That is/was one serious tube for that transmitter. Keep up the good work and bring us some more of this vintage transmitting equipment!

  • Harris makes a 2 megawatt MW transmitter, the DX2000, which is available with either air or liquid cooling:

    Some of these are in use in Asia and in the Middle East.

    R. Fry (Harris retiree)

  • Funny One

    Hey, you remember correctly and there ARE infact some strong transmitter sites in Germany (for example a 2 MW transmitter in the south-west broadcasting Europe 1 or the old site of Wertachtal which was previously used by a public broadcaster (Deutsche Welle) and had several 500kW transmitters). Also to remember: Wachenbrunn in the county of Thuringia still broadcasting Voice of Russia at 800 kW. Cool blog!

  • Gabe McKinney

    This is one of the first Megawatt transmitters built for Saudi that were installed in 1978. JO Weldon done the layout of the first one built. Joe Sainton did the Modulator and I worked with him and designed the cabinet. Charles Oney did the Power Amplifier design and the cabinet. George Woodard and Paul Kittenbacher did the layout of the power supplies. George designed the crowbar unit.
    I did unit 10 air cabinet and the air systems duct work and all the transmission lines. Bob McDonald was the project manager.
    Thanks Gabe McKinney 2-3-2014

  • Igor Pifat

    A similar Continental 2 MW TX was installed in what was then Yugoslavia in the 1970s. It served the Radio Belgrade on 684 kHz. The signal was easily picked up throughout the Middle East and North Africa, as well as Western Europe, where many Yugoslav expats worked. The TX site was bombed in the NATO campaign during the spring of 1999, and then abandoned.

  • Emily Taylor

    North Korea has a few pretty impressive stations on MW as well with output like that. 250kw 500kw, 1000kw and even a couple 1.5 million watt stations one of which uses a directional array pointed towards japan and can be heard in the daytime!!!! Its crazy!!

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