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Ebay SSPA 40W Power Amplifier module for 13cm - Doherty Amplifier


Paul Randall G3NJV
 

Quick question, these modules contain two devices each capable of 130W CW, yet the amplifier only gives 40W.
Is there a "simple" modification that can be performed to improve this?
I imagine I'm not the first person to consider this.
Paul


Robin Szemeti - G1YFG
 

I believe you can increase the bias on the "Class C" device to a similar level to the class A/B device ... I forget which one is which. that helps.  Remove the circulator amd bridge the gap ... that helps.

I assume your spreaders arrived OK?


On Tue, 13 Oct 2020 at 14:52, Paul Randall G3NJV <paulfrandall@...> wrote:
Quick question, these modules contain two devices each capable of 130W CW, yet the amplifier only gives 40W.
Is there a "simple" modification that can be performed to improve this?
I imagine I'm not the first person to consider this.
Paul


--
Robin Szemeti - G1YFG


Chris Bartram G4DGU
 

Hello Paul

Those amplifiers will be designed to give a combination of good linearity and efficiency at the 40W level, and the input/output matching will reflect that.  It may be that the modulation scheme for which they were designed had a fairly large peak to mean ratio, in which case the amplifier will probably give significantly more peak output power, but then you may run into problems with dissipation. The dissipation/current carrying ratings of the associated networks and cooling arrangements may also be challenged. Having said all that, the only way to find-out without more information than is probably available is to try - if you are prepared to take the risk! I suspect you may get a couple of dB more out, but you are likely to reduce the lifetime of the amplifier significantly.

The Doherty amplifier is usually used as a means of improving efficiency, and thus reducing the electricity bill of the user. I looked carefully at the potential of this technique for use in amateur amplifiers a few years ago, but came to the conclusion that it didn't offer a significant improvement in performance in amateur service.

73

Chris G4DGU


On 13/10/2020 14:52, Paul Randall G3NJV wrote:
Quick question, these modules contain two devices each capable of 130W CW, yet the amplifier only gives 40W.
Is there a "simple" modification that can be performed to improve this?
I imagine I'm not the first person to consider this.
Paul


Robin Szemeti - G1YFG
 

On the larger "nokia" style board, with 2 x double-die devices at an angle, I can state (and provide the burnt evidence to prove it ... ) that the output track will not take much over 150W ....  the devices will certainly produce it, I was able to pull a good 15A at 28V .. but the poor old track did not like it one little bit! I've limited myself to 10A on a good whistle now, I think that is more than enough.

On Tue, 13 Oct 2020 at 16:52, Chris Bartram G4DGU <chris@...> wrote:

Hello Paul

Those amplifiers will be designed to give a combination of good linearity and efficiency at the 40W level, and the input/output matching will reflect that.  It may be that the modulation scheme for which they were designed had a fairly large peak to mean ratio, in which case the amplifier will probably give significantly more peak output power, but then you may run into problems with dissipation. The dissipation/current carrying ratings of the associated networks and cooling arrangements may also be challenged. Having said all that, the only way to find-out without more information than is probably available is to try - if you are prepared to take the risk! I suspect you may get a couple of dB more out, but you are likely to reduce the lifetime of the amplifier significantly.

The Doherty amplifier is usually used as a means of improving efficiency, and thus reducing the electricity bill of the user. I looked carefully at the potential of this technique for use in amateur amplifiers a few years ago, but came to the conclusion that it didn't offer a significant improvement in performance in amateur service.

73

Chris G4DGU


On 13/10/2020 14:52, Paul Randall G3NJV wrote:
Quick question, these modules contain two devices each capable of 130W CW, yet the amplifier only gives 40W.
Is there a "simple" modification that can be performed to improve this?
I imagine I'm not the first person to consider this.
Paul


--
Robin Szemeti - G1YFG