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Pure signal?

Bill -VA3WTB
Bill -VA3WTB Member ✭✭✭
edited July 2019 in SmartSDR for Windows
I received this email from some one today. I am putting in some of his comments. We talked about pure signal and he can't understand why Flex radios are so bad on transmit. I didn't think they were that bad, and the 6000's are no better. Is it true the finals are dirty?


  • Bill -VA3WTB
    Bill -VA3WTB Member ✭✭✭
    edited February 2018
    I forgot his comments, here they are..
    It's the dam solid state finals on xmit that seem to be  causing all the increased IMD on the bands .
    not only on ssb but on the digital modes. the IMD goes out to > 10kc. and yes that's a fact.
    As Amateurs, we need get educated and demand, yes demand the mfg to clean up their radios.

    the flex series (1500-6700)does not meet their published spec's and its been 2.5 years !

  • Mike
    Mike Member
    edited August 2014
    Perhaps we can see what is going on. When my 6300 displays what I am transmitting, where in the signal chain am I looking? I'm thinking right where the signal is being generated, based on the displayed levels. Can I look at my own output to the antenna by opening up another slice on the other antenna connector, with the connector shorted? That should give a clearer picture if that technique works. --Mike, WV2ZOW
  • Neal_K3NC
    Neal_K3NC Member ✭✭
    edited August 2014
    Its amazing how many 'Great audio' reports these dirty finals produce. The person I suspect you are talking about has a thing about 12v finals and hates any rig with them (he has modified his rig to use  50v finals). We can wait for the arrl test of the 6000 to see if they report on the quality of the transmit side.

  • Bill -VA3WTB
    Bill -VA3WTB Member ✭✭✭
    edited February 2018
    He is using an Anan with pure signal
  • Neal_K3NC
    Neal_K3NC Member ✭✭
    edited August 2014
    The basic idea of predistortion was raised during the early days of the 5000 if my memory is correct and I remember Gerald talking about the possibiliies even back then. Gerald has committed that Flex will do predistortion but it must wait for release 2.x.

    Stay tuned.
  • np2g
    np2g Member ✭✭
    edited November 2015
    The 2014 ARRL Technical Innovation Award went to Warren C. Pratt, NR0V, of Santa Cruz, California. Pratt was cited for his research leading to the development of PureSignal, adaptive baseband pre-distortion algorithm used to improve the linearity of amplifiers and reduce intermodulation distortion products emitted by software-defined transmitters.

    All the flex radios pass the required FCC IMD spec.  Can the IMD be reduced   . YES !

    Running Pure Signal will Impact the ham Bands (For the positive )
    Pure signal  does reduce the IMD to -40  -50  -60  DB-. By the way there are  Flex 5,000's running "Pure Signal"  out there already  And they sound FANTASTIC 

    This is a pretty profound adaptation.  Flex has promised to release it for the 6000 series . 

    And If you think now you are "getting great audio reports " Stand back You don't really know how big this is going to get !!! 


  • Dave - WB5NHL
    Dave - WB5NHL Member ✭✭
    edited February 2017
    Sherwood does touch on one aspect in his Dayton presentation - 12 volt finals. It seems going with 50 volts has an inherent advantage. I don't have insight into all the engineering tradeoffs of using higher voltages but Sherwood does make a point that a base station (ve. mobile) radio probably should have 50 volt finals.
  • Mike W8MM
    Mike W8MM Member ✭✭
    edited July 2019
    I find talk of improved transmitter IMD performance to be somewhat amusing, depending on the OM asserting the argument.  Good xmit IMD is the mark of a polite and courteous operator consuming no more bandwidth than required for the function.

    However, in certain contesting environments, great transmitter IMD can be a handicap to "holding" a frequency.  It turns out that one cannot operate close in frequency to a very loud run station without ruining one's own rate because of the buckshot and splatter from a poor IMD station.  They don't hear you because your transmitter is clean enough not to bother them, but they sure bother you when they slide up or down to within "annoyance bandwidth".  What to do?  Keep slowing your own rate because you can't copy the calling stations underneath their crud, or slide away in frequency hoping to find a clear channel?

    One way to "fix" the problem is to INCREASE one's own transmit bandwidth to match or slightly exceed the aggressor's BW to force a run-rate standoff or coax them away from your run frequency.  I know of some Eu contest ops that used to put a variable resistor to ground across their ALC lines to be able to "adjust" their transmit BW on the fly.

    I hope that Pure Signal and/or other IMD reducing technologies proliferate.  I'll enthusiastically use them.  Just be aware that it might not help your contest scores ;~)
  • Neal_K3NC
    Neal_K3NC Member ✭✭
    edited November 2015
    It is amazing technology and Warren is one of the most amazing guys ever to grace our hobby! The predistortion mechanism is neat because you can place the rf sampler after your amplifier and have the radio predistort the whole chain's amount of distortion for excellent signal quality.

    Yes I also have a 100D!
  • np2g
    np2g Member ✭✭
    edited November 2015

    A fact of life on any continent.

    Thank goodness that all con-tester's  aren't all  that way.

    My  congrats are out there to those who don't and still win.

    Now: The subject is Pure signal .

    Pure signal or adaptive pre distortion whatever you wish to call it will  considerably improve that IMD product. The reward is a cleaner, louder, more energy efficient , signal presentation than is presently out there (Excluding those who have already taken this step.) 

    IMD distortion products by FCC  are presently  defined . Like anything else in the world, just possibly, that number , should be dropped to -40db . Then that wish of those 50 V finals will  show up more often .

    Technology advanced radio's  Like the SDR Radio's, Like Flex  should have "Pure signal" , Pre Distortion , and whatever else  the latest and greatest improvements know to man is out there . That's called" state of the art." 

    Its like being a sled dog in a sled dog race . Either you are the lead dog or the view has dramatically deteriorated .

    I look forward to Flex's commitment to  "Pure signal"      I will absolutely use it . Yes I will sound better , My signal will improve , and the HAM neighborhood will flourish. 

  • np2g
    np2g Member ✭✭
    edited November 2015
    The sampler belongs after the amplifier that way it corrects everything. 

    Just in the radio alone you do see a reduction in IMD for sure. And the Amplifier. since it now has a cleaner input ,also flourishes .      But be all you can be ...... Let it sample that final stage and correct there  >>>>>

    Real world numbers are unbelievable  as much as -60 DB  on the ones I have seen implemented . image
  • Paul Christensen, W9AC
    Paul Christensen, W9AC Member ✭✭
    edited November 2016

    Apache has shown that a 50V PA isn't a requirement for excellent TX IMD performance when APD linearization is used -- and as long as the traditional BJT or MOSFET RF power transistors have reasonably low memory effect to thermal junction change. 

    A 50V PA is no guarantee of low TX IMD.  When the ARRL tested the Ten Tec Omni Six back in 1993, the measured unit showed -39 dBc 3rd-order IMD on 20m at 100W.  The Omni Six runs on +12V.  Compare that to the elevated-voltage PA transceivers from Icom and Kenwood.  

    I've nothing against a manufacturer starting out with a 50V PA, but the data show it's not a requirement to achieve low IMD when good RF design technique is used. 

    Paul, W9AC


  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited March 2017

    For your question, as asked, the answer is no, the finals of our transmitters are not "dirty".

    The FCC is the federal regulatory body that specifies the maximum allowable spurious emission as per Part 97.307 (d) and subpart (e).

    "(d) For transmitters installed after January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must be at least 43 dB below the mean power of the fundamental emission.  For transmitters installed on or before January 1, 2003, the mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency below 30 MHz must not exceed 50 mW and must be at least 40 dB below the mean power of the fundamental emission.  For a transmitter of mean power less than 5 W installed on or before January 1, 2003, the attenuation must be at least 30 dB. A transmitter built before April 15, 1977, or first marketed before January 1, 1978, is exempt from this requirement."

    "(e) The mean power of any spurious emission from a station transmitter or external RF power amplifier transmitting on a frequency between 30–225 MHz must be at least 60 dB below the mean power of the fundamental. For a transmitter having a mean power of 25 W or less, the mean power of any spurious emission supplied to the antenna transmission line must not exceed 25 μW and must be at least 40 dB below the mean power of the fundamental emission, but need not be reduced below the power of 10 μW. A transmitter built before April 15, 1977, or first marketed before January 1, 1978, is exempt from this requirement."

    Our radios meet or exceed the aforementioned requirements.

    On the issue of if and when we plan to offer adaptive predistortion as a feature in the FLEX-6000 Signature Series SDRs, that question has been answered in a previous post ( https://community.flexradio.com/flexradio/topics/adaptive_predistortion)
  • Chris Tucker
    Chris Tucker Member ✭✭

    How are there FLEX 5000's out there running Pure Audio and CESSB ? Is there a version of Power SDR that has these built in ?

  • Mike-VA3MW
    Mike-VA3MW Administrator, FlexRadio Employee, Community Manager, Super Elmer, Moderator admin

    CESSB is in the PowerSDR code and has been for some time.

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