Re: 2320 PA Modifications?

Clint Sharp <cjaysharp@...>

Not necessarily looking for more power or gain, either or both would be nice of course but, primarily, I am looking for knowledge.

Reading the application notes for LDMOS devices in Doherty amplifiers is interesting but hasn't yet answered all my questions and I'm learning.

On Thu, 22 Oct 2020, 16:04 Robin Szemeti - G1YFG, <robin@...> wrote:
I'm not sure you'll get more power out, you may get more gain.   Remember that in "Doherty" mode, the Class A/B side can be driven hard into clipping, the peaking side then picks up the slack .... its very similar to a "Class H" audio amplifier in some respects.  So while you could re-bias it into Class A/B both sides and they will still sum correctly due to the phasing, you'd have to back the drive off so the devices did not clip .. you, get more gain, but probably the same power, with less efficiency.    That's my take on it anyway.  

On Thu, 22 Oct 2020 at 13:38, Clint Sharp <cjaysharp@...> wrote:
As these boards have 'sense' FETs would that suggest they're using an automatic biasing scheme like the one shown in Ampleon's Doherty Amplifier App notes?

Should make it more simple to modify the biasing no?

On Thu, 22 Oct 2020 at 13:23, Robin Szemeti - G1YFG <robin@...> wrote:
The "other" type of board as per P27 of the PDF is easier to remove the circulator, 4 bolts.   I took a piece of brass bar, 10mm square, drilled a 0.141" hole through it at just the right height and soldered a piece it UT141 hardline through it with the centre conductor at board height.  Bolted down, it removes any possible strain on the junction.

On Thu, 22 Oct 2020 at 12:02, Richard White <gi4doh@...> wrote:
Not the neatest of modifications but this worked for me - if I were doing it again I would probably just wire round the circulator- I removed in in slices with a Dremel. But perfectly functional.
Other mods got a bit more oomph out of it.
73 Richard GI4DOH

Robin Szemeti - G1YFG

Clint. M0UAW IO83

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Robin Szemeti - G1YFG

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