Wideband RF amplifier easy

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neazoi

I would like your comments on this amplifier when used as an HF (1-30MHz) one.
I see from the 2sc1971 datasheet that it can be driven with as low as 50mW, probably even lower and it can still output 1-2W
The final transformer is used as a voltage step up I think.

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BigBoss

But pay attention the last stage because it looks like a B or C-Class Power Amplifier.If it's so, AM modulated signals will loose their envelope.
It's also strange that of being the last transformer "step-up". Normally output impedance of a bipolar higher than load but I haven't examined so that's why I cannot say something consistent.

betwixt

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I agree with BigBoss, be cautious of it's linearity.

Note that the current it shows as 30mA is nonsense, the bias supply uses about 15mA and from experience of using 2SC1971 devices, you will be exceeding the 2A collector current maximum to get 10W out of them. Having said that, they are quite robust devices and seem to tolerate excessive current for short periods in SSB PA stages. Possibly the 30mA refers to quiescent current with no RF drive.

The 1S1588 has a Vf of about 0.7V at the ~15mA it passes so it isn't far off the bias point of the transistor but you can use 1N914/4148 as substitutes as long as they are thermally bonded to the heat sink.

Brian.

neazoi

I agree with BigBoss, be cautious of it's linearity.

Note that the current it shows as 30mA is nonsense, the bias supply uses about 15mA and from experience of using 2SC1971 devices, you will be exceeding the 2A collector current maximum to get 10W out of them. Having said that, they are quite robust devices and seem to tolerate excessive current for short periods in SSB PA stages. Possibly the 30mA refers to quiescent current with no RF drive.

The 1S1588 has a Vf of about 0.7V at the ~15mA it passes so it isn't far off the bias point of the transistor but you can use 1N914/4148 as substitutes as long as they are thermally bonded to the heat sink.

Brian.

Thanks all for your replies, you saved me some .
For circuit simplicity, I am trying to see how much power can I get from 1mW of input power or so with just one power transistor. A 2sc2166 did not work ok in this context and in it's datasheet it is specified for 100mW of input power min.
This 2SC1971 is specified for 50mW and even less.
Obviously someone wants to build a two transistor simple broadband HF linear...
I have to mention that my TX will be on/off (CW) so I suspect it does not need to be linear.

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