a less power circuit?

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a less power circuit?

Postby lu4fse » Tue Feb 11, 2003 10:11 am

Hi, first sorry for my bad english (here we speak spanish)
I'm writing to ask if does exist some circuit of a class e rf transmitter with 1 or 2 fet's something like 100w or less?

Thanks in advance

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Lower power transmitters

Postby steve_qix » Wed Feb 12, 2003 7:58 am


You can take the existing design for any of the class E transmitters, and reduce the number of MOSFETs, and change the shunt capacitor.

Each FQA11N90 MOSFET is capable of about 50 or 60 watts of RF power input.

So, for 100 watts, use 2 FQA11N90 MOSFETs. Since your load impedance is lower, you need to lower the shunt capacitor. I would use a shunt capacitor of around 300 pF to 400 pF with 2 MOSFETs.

Your gate drive requirements will be lower. With two MOSFETs, I would drive the gates of the final RF amplifier MOSFETs directly with an RF source, if you have an RF source available (such as an SSB transmitter operating in CW mode).

If you plan on using the class H modulator, you can safely use 2 MOSFETs in each leg of the modulator, instead of 4 MOSFETs.


Visit the class E web site at:

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