New Broadcast Electronics TX not class E

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New Broadcast Electronics TX not class E

Postby John K5PRO » Wed Apr 20, 2005 6:06 pm

I got a good look at the new BE 50 kW AM rig at NAB this week. Co-designer Jerry Westberg went over it w/me, looks pretty interesting. A new idea for higher efficiency ham amplitude modulation? Nah. They ditched class E and went for even higher efficiency using RF PWM, generated with DSP. Unless you guise want to wind your own DSP code, this thing would be tricky to try and build at home. There is no power transformer, and it has a bunch of switching power supplies as well as RF modules. Output combiner is simple summing network with T transformation. He used litz wire for the inductors and big micas for the caps. Did i mention that its supposed to run 88% efficient from line in to rf out? Also, it weighs about 1100 # total, and covers the same footprint as the old Raytheon RA1000! It should give the Harris digital 50 a run for money, as it looks simpler and cheaper to build....

Interesting that Continental did RF PWM (and had an expired patent from 1982) with years back and abandoned that. Didn't have the DSP power that can do a lot more now in creating pulse width variations for the RF carrier in response to modulation. It is NOT a solid state ampliphase.
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Continental RF PWM

Postby NE4AM » Wed Apr 20, 2005 11:35 pm

As I recall, the Continental RF PWM rig ran the PA's from 73 volts to try to limit the switching losses. The key to the BE transmitter is some special *magic* that keeps the switching losses low, running from a much higher B+.
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keeping switching losses low

Postby John K5PRO » Thu Apr 21, 2005 2:47 pm

Did they use your driver circuit from the Class E rigs?
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Postby NE4AM » Sat Apr 23, 2005 7:52 am

Nah, the state of the art has advanced a lot since then. Jerry W. came up with a really neat, simple driver circuit.
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