Pulsating Mic Stream while transmitting FT8

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  • Updated 6 months ago
  • (Edited)
Stupid system.....logged me out while I was typing....OK, shorter version:  there is a 'pulsating' noise and visual (on Mic Stream on the DAX) when transmitting on FT8, 20 m.  Rig is a 6300, V 2.1.33.  Was working fine for a while, just noticed this as replies to contacts dropped off.  OK, further info:  seems to be an ATU issue.  With the ATU turned off, the pulsing stops BUT the SWRs go up to about 1.7 or a bit higher.  SWR has never been an issue with the TransWorld antenna, better go see if it has ants!
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Russ Locke

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Posted 6 months ago

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Jim KJ7S

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I have had a problem with tx power stability, bit only when I am approaching the top or bottom of the tx bandwidth edges. For example when I am say, at 2950 hz and the tx bandwidth is set for 3000 hz,, it will begin to pulsate between a lower power level and higher. Just a thought.
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Russ Locke

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Thanks for the thought.  Since I posted this I tried additional 'experiments' and found that the ATU is NOT the problem; I get the 'power pulses' with it on or off.  Problem is very intermittent in that one 15 second tx may be pulse free and the next is not.  I have been able to make a couple contacts since noticing the problem but they all have been NA calls probably were able to receive my signal with the 'on' sequence of the pulse.  I'm leaning towards a sound card or transmitter problem now but am so new to both digital modes and SDR that I'm not sure which to look at first.
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Bill NE1B

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I have seen this problem on FT8 also with a laptop on the LAN using DAX between WSJT-X and Smart SDR V2.1, even 1.9.  My laptop is a WIN7.  It seems to be within the laptop and its handling of DAX.  As you say "a soundcard" problem.  The DAX works fine for 2 days and then causes pulsation or distortion of the transmitted signal.  I simply STOP and RESTART DAX to "clean it up"!
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Tim - W4TME, Customer Experience Manager

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Russ,  Check the CPU utilization of the PC when running WSJT-X.  If you are running at 70% or better, WSJT-X is overtaxing your PC.