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Thermal expansion noise on Flex 6300

NK9BNK9B Member

I recently started noticing an occasional ping/short crackle that sounds like thermal expansion noise in the rig (I assume PA area). I can't really localize it. It happens with high duty cycle modes like JT65. I've read where the PA transistors are very robust and rated for 100% duty cycle (not ICAS). I don't run the rig at full power, but JT65 does cause the PA to work a little. :-)

Any thoughts on whether this is something to address? 


-Jason, NK9B


  • Bill -VA3WTBBill -VA3WTB Member ✭✭✭
    edited February 2018
    Just one thing..it can not over heat, no matter what you do. Everything is well protected.
  • Dick BDick B Member
    edited May 1
    Since most running JT-65 are using 20W or less I wouldn't think that is a problem at all.  Hope you're not running significantly more than that.  
  • K1UO - LarryK1UO - Larry Member ✭✭
    edited July 2017
    Remember JT65 ,or any JT Mode for that matter, is not a low power mode...  It is ,however, a weak signal mode and at times may require 500 watts or even a kw to make a very very weak signal contact.  Lowband operation using JT Modes comes to mind.
  • Ian1Ian1 Member
    edited July 2017
    Larry My signal has hit everywhere the I have ever scene with never more then 30 watts. I'm not trolling only wondering why you think this as I saw a similar comment from another Poster on the WSJT-x user group the other day? Ian
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited July 2017

    Fact of Life.. JT Modes are NOT Low Power Modes but rather are Weak Signal Modes   

    The low power misconception is a legacy of PSK which is ultra sensitive to IMD products and has less relevance to JT Modes which were originally designed for Moon Bounce using high powered transmitters.

    Have you ever tried to work a -29 db Signal on JT?.. I found that most weak signal below about -26dB did not copy me until I boosted the power to 1500W or about 12KW ERP.

    Of course, when boosting power you have to make sure that you are not splattering all over the bands but the Flex gives you a pretty good indication of what you are sending by keeping the XMT out of the red and even yellow zones on the XMT Audio meter

  • Ian1Ian1 Member
    edited July 2017
    Howard trust your doing well.

    WSJTX on the left side shows signal in DB from my QTH a minus 26DB signal can be reached typically with 30 watts.

    I asked the question because I have not seen a station at -26 that can't see my signal.

    My station doesn seem to do well below that reading.

  • KevinKevin Member
    edited July 2017
    Howard... have a question. You mention "by keeping the XMT out of the red and even yellow zones on the XMT Audio Meter." I had read, here or in the books, that I only have to make sure the peak indicator doesn't turn red.

    With PSK, this setting gives me about -28 to -30 dB IMD as read by my old PSK Meter. Not bad numbers. Am I running too hot? The graphic below is typical for me on JT65. Never any red but also not down in the green which, if set there, would significantly reduce my output power.


    Kev K4VD
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited July 2017

    Looking at the peak yellow it seems a bit hot

  • Tim - W4TMETim - W4TME Administrator, FlexRadio Employee admin
    edited July 2017
    Keep the peak indicator (max) below 0 dB for digital modes.  The image above is a little too hot as Howard eluded to.
  • KY6LA_HowardKY6LA_Howard La Jolla, CA. Paris and Sablet FranceMember ✭✭✭
    edited July 2017


    I try to work the really weak ones because they are usually the interesting DX.

    I now have many contacts down to -29dB on JT65 which is my record low... I found that below -26dB.. I had to continually up the power until they heard me.

    Playing around with FT8...I can get away with low power (under 50 W) to about -16dB but then I need to up the power to be heard.--my record low is -19dB on FT8

    OTOH... I really have no idea how much power and what antennas the other guys is using... so the weak ones could be running 1W into a vertical vs my big beam.

    Bottom Line.. on the various JT Modes when trying to work weak signals up the power to see if it helps.

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