Re: Nokia pa on 13cms? - Doherty
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David GM6BIG
Hi Robin,
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Doherty amps work in a less obvious way. The Carrier device could easily be running 10 times the current of the Peaking side. The two sides may be biased differently. The are moderately narrowband, there is much 1/4 wave phasing in there. The method has been around a long time, so lots on the web to read up on them. Essentially, instead of increasing the PA volts (Carrier device) to get more power, decrease the Carrier load impedance (Using the Peaking device)... This will get you started... https://www.electronics-notes.com/articles/radio/doherty-amplifier/design.php https://mengtianyu.wordpress.com/2010/02/09/the-doherty-amplifier-new-after-70-years/ https://www.radioworld.com/columns-and-views/reinventing-bill-doherty-and-his-highefficiency-amplifier An early use of the method was in big AM transmitters, an efficient way to make AM RF without a big oily and expensive audio rated modulation transformer. Not so easy to move in freqy, but ideal for, say, an AM broadcast transmitter... Now applied to microwave stuff...! Cheers, DAvid
On 12/09/2020 22:52, Robin Szemeti - G1YFG wrote:
In theory, it is supposed to run in Doherty mode .. the transistor on the right biased into Class A/B and pulling about 1.8A quiescent ... the one on the left turned hard off and only coming on with peaks. --
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