Technical Question Regarding APD-SmartSignal and Polar Modulation

KD8MKG

I would appreciate if you all could help me understand something.

Flex claims that "APD should remain enabled at all times during normal Aurora operation. Disabling APD can result in degraded signal quality and is not recommended."

This implies an interesting admission about the polar modulation architecture; and one that isn't really an unknown: polar modulation amplification is behind the 8-ball when compared to well-executed Class-AB linear PA with a reasonably linear transfer function, operated within its nominal limits. In other words, the uncorrected polar-modulation architecture may begin from a non-trivially less linear starting point, because SmartSignal must correct not only ordinary PA nonlinearities, but also errors specific to the polar architecture: envelope/phase-path alignment, AM-AM and AM-PM distortion, envelope-modulator behavior, memory effects, and so forth.

I understand that APD/SmartSignal can model, detect and correct the entire composite transfer function, including any polar modulation-specific nonlinearities, but certainly not in an unlimited fashion. This type of servo-adjacent correction is always necessarily bounded by available amplitude headroom, phase and timing authority, correction bandwidth, model fidelity, converter dynamic range, and the invertibility of the underlying transfer function.

So here's the question: Does Aurora’s SmartSignal implementation have sufficient correction range and hardware headroom to bring its final transmitted output into the same performance range as a well-designed, conventional, linear PA using equally capable APD? Or does the polar modulation PA's presumably poorer linearity consume enough of the correction budget that the final result remains inferior when compared against a reasonably well-designed Class AB linear amplifier with equally-capable APD?

KD8MKG

Hmmm... upon reflecting, I've realized that there may be no detailed public answer that is practical, since it asks about internal correction margins and references a comparison against a hypothetical conventional architecture that was poorly defined on my part.

Perhaps a more easily answered question would be something like:

Are there published measurements for the production Aurora's SmartSignal corrected output at 500 Watts... particularly, two-tone IMD3/IMD5, occupied bandwidth, and adjacent channel spectral performance?

I would also be interested in any testing performed with high-density SSB audio, in addition to any two-tone testing. My practical concern is whether a heavily processed but properly band-limited ESSB signal can remain pristine after the polar modulation TX and APD correction.

A comparison against a FLEX-8000 and Power Genius XL operating with SmartSignal would be quite informative, but even standalone Aurora measurements would help answer the practical part of my original question ahead of a purchase decision.

Thanks!

David Decoons, wo2x

I can state when on 80 meters where signal is S9 +30, my AU510 @ 500 watts is as clean as my 8600/PG XL @ 1200 watts.both with APD enabled.
Two different receiving stations cannot detect artifacts outside my TX bandwidth. Also if they switch to the opposite sideband they cannot hear me.

While this does not provide empirical measurements, it does give you feedback on real world performance.

In the summer, I am using the Aurora 95% of the time as my RF equipment is in a non air conditioned garage.

73 Dave wo2x

KD8MKG

Thanks for your input!