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APD in my lifetime?

Member ✭✭
edited May 2020 in FLEX-6000 Signature Series
I bought a 6400 a couple months ago primarily because I wanted to try out SSDR.  Well, the software is great but it has many features I don't use and lacks one that I'd really like to have - APD.  I've read all the threads on this topic as well as Gerald's recent announcement but still don't have any idea when (or if) APD will become a reality.  If it's way down on Flex's priority list then I'm probably going to sell the 6400 and move on to an ANAN rig.  But before I take that step, I'd like to ask if there are any outstanding rumors or inside dope about when or if Flex will get to it in the near future.  Thanks.

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Answers

  • Member ✭
    edited December 2019
    what is  APD?  
  • Member ✭✭✭
    edited December 2019
    Adaptive Predistortion, aka “Pure Signal”, an Anan feature.
  • Member ✭✭✭
    edited December 2019
    Hi Jerry,
    This thread below is 5 years old but provides a good description as well as the Flex position on APD and their policy on not announcing features or dates.  

    https://community.flexradio.com/flexradio/topics/official-position-on-adaptive-predistortion

    Regards, Al / NN4ZZ  
    al (at) nn4zz (dot) com




  • Member ✭✭
    edited December 2019
    Adaptive predistortion linearization, *adapted* by Anan, but not invented by them. See, for example:
    http://www.summittechmedia.com/highfreqelec/Apr04/HFE0404_Stapleton.pdf
  • Member ✭✭
    edited December 2019
    Rod: I find that distortion products seem to be <60dB down (or better) from carrier with my Flex6400... at least casually, by observing my spectrum while transmitting. Why are you concerned about having APD given the spectral purity already attained by the Flex Signature Series?

  • Member ✭✭
    edited January 2020
    Mike - K6QY

    I'm not getting anywhere remotely close to what you are claiming.  OTOH, I'll admit that my spectrum purity is somewhat better than other rigs I've measured.

    But I'm running an amp and the amp contributes more IMD.  With APD I could sample the amp output and feed it back into the 6400 thereby including the amp in the "cleanup" process.
  • Member ✭✭
    edited December 2019
    Rod: I certainly don't disagree that it would be cool to have this feature! So, now you have me curious, after having made that assertion about my spectral purity. I have an Agilent 20GHz spectrum analyzer and just got a kit for sampling my RF output (basically a kW directional coupler). I'll get this set up and do some serious measurements of the distortion in my 6400's output, and the output after my PA!  Something I've been meaning to do...
  • Member ✭✭
    edited December 2019
    Mike - k6qy

    If you can, feed the mic input from a two-tone generator and run your rig at full power.  That's one of the best tests for IMD. The two-tone generator should have harmonic distortion less than -55db.  Most of them do.
  • Member ✭✭
    edited December 2019
    Will do. I teach this to my students!
  • Member ✭✭
    edited December 2019
    Flex made this comment when releasing the results of their poll of user priorities this summer:

     “.... the survey was very helpful in revealing the relative importance of noise mitigation and pre-distortion. We have heard these messages loud and clear and have already begun discussions on next steps to make improvements in these areas of performance.”

    So APD may finally be getting traction.

    Howard
  • Member ✭✭
    edited December 2019
    Yes. Facts would be helpful in this case to understand the pain vs gain, so to speak.
  • Member ✭✭✭
    edited December 2019
    As was just mentioned, it was on the customers survey and was near the top of the most wanted feature.
    Rod are you bothering stations around you? Are you splattering? I hope if Flex does give us this feature they do a better job than the software used on the Anan hardware. On any day my IMD is around -40, I don't bother anyone around me,,is that not what it's all about?

    To me the ADP sounds very processed the way most have it set up. I don't care for that sound. I hope Flex can make it sound very natural.

    To the question? none of us know what the time table is for this feature.
    So if the ADP is a real deal breaker, then you already know your answer.
  • Member ✭✭
    edited December 2019
    Bill: How did you measure -40dB? Is that the result of a two-tone IMD measurement? Tnx.
  • Member ✭✭✭
    edited December 2019
    When we get into discussions of QRO IMD, I usually tell folks that if they care about linearity, the thing to do is to operate well below maximum power, minimizing supply droop and thermal issues.  (Say 3 dB down = 1/2 S unit.)  APD would be great, I agree, but mostly to the extent of letting you feel good about running at the full power level. 

    I worked with "Pure Signal" on an Anan 100D.  It did pretty well, but it was tricky to set up.  To be very practical, we need a fully automated linearization that works on all bands, with a wide range of power / SWR levels, modulation types, etc. Maybe the Anan guys are doing better now.  It should be doable for Flex, but I can see why they haven't been eager.

  • Member ✭✭✭
    edited December 2019
    I had other stations do the measurement on my transmited signal. A Flex should obtain -40db when properly set up.
  • Member ✭✭✭
    edited December 2019
    In the scheme of things I see a greater ROI elsewhere. Greater fish to fry, personally this isn't a feature I would hang my hat on as a deal breaker.
  • Member ✭✭✭
    So... I've read the referenced posting "Official Position on Adaptive Predistortion. Many times. Many times, over the past 8 years in fact. I've seen spectral images on the Web, in ARRL publications, and off-the-air. There is absolutely no doubt that PureSignal / Adaptive Pre-Distortion is a huge improvement.

    Another couple of years and Flex will achieve an entire Decade of Denial. There is no doubt that Flex has made noticeable and substantial improvements over the years and across new models in many other areas, but not APD.

    I believe in APD so much that I've put my $$$ where my mouth is: my old tube-amp has had a tube-swap and bias-change to drive the 3rd order IMD to -45dBC, and I've added a -60dB output-coupler. I'm just waiting for Flex to do something :-) and I live in hope of seeing commercial (CATV) specs like 3rd IMD -60dBc. 10 years after ANAN achieved it should be enough time... Let's do this one thing, do it right, and put it to bed forever; 8 years of waiting is too long already!
  • Member ✭✭

    APD was developed by Dr. Warren Pratt, NR0V and adopted by Apache Labs into their ANAN radios. I don't know if this arrangement is proprietary to Apache. And I don't know the business arrangement between Apache and Dr. Pratt. But I think it would be worth a phone call to Dr. Pratt by somebody at Flex to inquire. If Flex is too busy with other things to develop their own version of APD, then it might make a whole lot of sense for them to work with Dr. Pratt.

  • Member ✭✭✭✭
    edited December 2022

    Adaptive Pre-Destortion has been around for a while. Warren Pratt adapted it for the Anan radios and called it Pure Signal. But, he didn't invent or patent the idea and method.

    James

    WD5GWY

    https://patents.google.com/patent/US4291277A/en

    US4291277A - Adaptive predistortion technique for linearizing a power amplifier for digital data systems - Google Patents

    https://community.flexradio.com/home/leaving?allowTrusted=1&target=https%3A%2F%2Fpatents.google.com%2Fpatent%2FUS4291277A%2Fen
    Distortion introduced into a multiamplitude signal format by a high power microwave amplifier is compensated by a system which adapts itself to non-linearities present in the amplifier and predistorts the input signals before they are subjected to the non-linearities created by the amplifier. The degree of predistortion is non-fixed and varies or is updated as the non-linear conversion characteristics of the amplifier change with time.


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