Re: Nokia pa on 13cms? - Doherty


David GM6BIG
 

Hi Robin,

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.
I'm finding I can pull about 10A through the right hand device, but barely anything through the left hand device, no matter how hard I hit the input. I've increased the drive by 6dB and its not really pushing it any harder ... something isn't quite right.
On Sat, 12 Sep 2020 at 20:53, militaryoperator via groups.io <http://groups.io> <Military1944=aol.com@groups.io <mailto:aol.com@groups.io>> wrote:
https://morepicture.webs.com/hamradio.htm
The Nokia pa for 13cm. I know about the circulator, removing etc,
but what about the bias. Has anyone sorted out better biasing for
this unit?
Ben
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