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push pull ab class, hf band power amplifier

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ali.mahzoun

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hello,
I want to analysis the schematic of 100W_PEP linear amp in RD100HHF1 transistor application note (ANVHF027B.Pdf), here questions:
1- How I can estimate the gain of PA in large signal?
2- Why designer inserted a 56Ohms resistor in feedback and how calculate this?
3-The input impedance of the PA how was estimated?
4-With the 13.8 supply voltage and a 1:4 output transformer (instead of 1:5), can I get 100W output power(instead of 130W)?
The schematic is attached
Thanks
 

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  • ANVHF027B(RD100HHF1 PP).pdf
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Dan Mills

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"Radio frequency transistors" by Dye and Granburg is the canonical book on this stuff, it predates LDMOS but the basic mathematics has not changed.

You may also want to consider the use of a ferrite loaded transmission line transformer for the output, limits you on ratios but usually beats a binocular and tube job for efficiency and bandwidth (HF + 6Mtr is typically possible).

I am betting that the transformer ratios and feedback values were derived somewhat experimentally, the maths gets you into the ballpark but there are always parasitics that you didn't take into account and usually some cut and try is indicated.

Regards, Dan.
 
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