Adaptive Predistortion

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  • Updated 5 years ago
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I see another SDR group is all abuzz concerning the OpenHPSDR Groups new Adaptive Predistortion breakthrough of obtaining greater than 50db IMD3 from a 13.8V 100Watt PA TX system and congrats to them for their work in helping clean up the TX side of things re signal purity. Is the development of similar Predistortion software on the agenda for the Flex 6000 systems at some point? Not a current show stopper for me.... just curious.
Larry K1UO
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K1UO - Larry

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Posted 5 years ago

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Steve - N5AC, VP Engineering / CTO

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Official Response
When we designed the FLEX-6000 we had adaptive predistortion in mind so we included a tap from the transmitter that feeds back into the receiver. This gives us simultaneous access to the desired and actual transmit spectrum in the FPGA so that we can implement linearizarion. We also have sensors for temperature, voltage and load match of the PA as these can be used to improve linearizarion. The work that needs to be done for the FLEX-6000 is to experiment with algorithms and input sources to determine what gets us the most bang for the buck and then finalize the implementation.

The FLEX-6000 already has the highest precision DAC of any amateur transmitter and excellent IMD numbers so we decided to focus first on features that the community is waiting for and return later for implementation of predistortion. Predistortion in the cellular business is critical because they are putting many carriers in a single PA and spectral purity when you're doing this is critical. But for ham radio, it is more of a "nice to have" and "nice neighbor" sort of thing -- it's not going to prevent someone from copying YOUR signal and the FLEX-6000 spectral purity is well above the legal limits. Barring significant hype that makes this a marketing issue, we'll look into this after finishing the items on the road map that you, our customers, have told us are important for you.

Since we thought ahead, you will not need to use an external device to tap the actual transmit signal and feed it back into the receiver when the time comes. Incidentally, our VP/GM of our government business, Graham KE9H, has considerable experience with predistortion having run a company that focused on predistortion in cellular PAs. He also developed PAs for HPSDR.