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Transmitting a JT9 signal around 2975 to 3025 Hz I get large Input Level Meter Fluctuations on my Fl

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Dick / KC9YRA
Dick / KC9YRA Member ✭✭
edited June 2020 in FLEX-6000 Signature Series

These large input level
meter fluctuations (-20 to -5 dB) do not affect the transmitter’s output (as viewed on a wattmeter).  The DAX Control Panel TX meter is stable.  2995 Hz seems to be the most sensitive while transmitting a JT9 signal.  I’ve seen this type of meter fluctuation since day one (May 2014 SSDR 1.2.1) on my 6500.  Only recently did I realize that this was very frequency sensitive.  I use WSJT-X (1.5.0) on DAX TX-1.  This is only a minor visual nuisance.

I found that by setting WSJT-X to 3000 Hz and pressing the WSJT-X Tune Button.  The input level meter will be stable at 3000 Hz.  While still transmitting adjust WSJT-X + or – 1 Hz.  The input level meter starts to fluctuate at what appears to be 2 pulses second rate.  Change frequency + or - 2 Hz the meter pulses at a much faster rate.  If you continue to increase or decrease the frequency by + or - 25 Hz the input level meter slowly stabilizes the further you move away from 3000 Hz.  Looks like it’s creating some sort of beat frequency at 3000 Hz and when the frequency is changed the meter is trying to display the difference.  Easily seen at + or – 1 to 2 Hz.

This problem has been duplicated with 2 different Win 7 computers that were each connected directly to my Flex-6500.  I have SSDR 1.5.1 currently installed.  The problem occurs on all Bands (80-6m), with an antenna or a dummy load, even with the RF Power set to Zero.  Transmit Filter Lo Cut=50    Hi Cut=4000.

Has anyone seen this problem on their Flex 6000 Series Radio?

Is this a WSJT-X or Flex problem?

I would appreciate if someone could try to duplicate the above problem and let me know the results before I contact FlexRadio.

Anyone wishing contact me directly use KC9YRA at arrl dot net


Comments

  • Mark Gottlieb
    Mark Gottlieb Member
    edited April 2017
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    My Win7 software will not send signal to radio, at all, above 2600HZ using WSJT-X.  So, I have had a similar problem.  
  • George KF2T
    George KF2T Member ✭✭✭
    edited February 2019
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    You are experiencing the roll off of the audio input filter. This can be adjusted in SSDR to open the transmit bandwidth to 4-5 kHz. Just remember to normalize things for SSB. You might want to set a digital transmit profile and a voice one to keep bandwidth straight. Note that this setting is NOT the EQ. Another thing to check is that you confirm that DIGU is the mode - regular USB shouldn't be used for digital modes. Finally, ensure you don't have any RF getting in or have another audio source possibly selected.
  • David Altekruse
    David Altekruse Member
    edited March 2017
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    I tried your experiment on my 6300 and WSJT-X v1.5.0-rc1.  My TX bandwidith is set to Low Cut: 0, High Cut: 5000 Hz.  (My receive bandwidth is set to 5.0K.) 

    I get similar results to yours.  Starting around 2995 Hz the frequency beating becomes obvious on the 6300 level meter.  As I go up in frequency, the beating increases.  At 3000 Hz the beating stops.  As I increase it further, the beating starts up again.  The effect is exactly the same as if I took two piano strings at the same pitch and then slowly changed the tuning of one of the strings.

    There was no visible effect shown on the DAX input to the 6300.  Nor was there any visible effect on the 6300 frequency spectrum display.  My guess is that the level display samples at 3000 KHz or some multiple of that frequency.   Since I don't see the effect on the spectrum display or on my external power meter, I don't believe this is anything more than a 6300 level display anomaly.

    -David, N1DNA
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited March 2017
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    Here is the explanation.  First off the metering is digital, not analog so it is being sampled at a specific rate (frequency).  The fluctuation you are observing is a "beat frequency" effect due to the interaction between the signal tone(s) and the time interval we are measuring signal strength.  

    It isn't a problem that needs to be  fixed since it is not effecting the signal, but a consequence of how the metering is done.  It is basically cosmetic.
  • Mark Gottlieb
    Mark Gottlieb Member
    edited April 2017
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    My problem is slightly different in that, for that frequency range on JT 9 (WSJT-X software) there is no outgoing signal on the radio.  I can see that on the Wattmeter and the Panadapter.  It only happens at the upper end aroudn 3000hz.
  • Tim - W4TME
    Tim - W4TME Administrator, FlexRadio Employee admin
    edited December 2016
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    Open your TX filter bandwidth wider.
  • Dick / KC9YRA
    Dick / KC9YRA Member ✭✭
    edited November 2015
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    George
    I did try to increase the Transmit Hi Cut to 5000 but not difference on the meter fluctuates.
    Thanks
  • Dick / KC9YRA
    Dick / KC9YRA Member ✭✭
    edited November 2015
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    Dave
    Thank you for test results. Helps knowing not my 6500
    **** 73
  • Ken - NM9P
    Ken - NM9P Member ✭✭✭
    edited June 2020
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    Are you using USB or DIGIU?  If you are using SSB, then the TX EQ and other processing may be messing with your signal...If not, then, hmmmmmm  Do you have the sample rates matching in the properties of both WSJT and the windows sound set-up utilities?  if you have one set at 48,000 and the other set to 44,100, then the conversion routine may be causing problems...

    Ken - NM9P

  • Dick / KC9YRA
    Dick / KC9YRA Member ✭✭
    edited November 2015
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    Tim
    Thanks for the rapid reply and explanation. 
    Sure glad this was not my 6500. Would be lost with out it.
    Can go back to chasing DX
    Thanks to FlexRadio for such a Great Radio

    **** 73
  • DH2ID
    DH2ID Member ✭✭✭
    edited March 2017
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    All soundcards set to 48k, 100% and DIGU slice to 5k in/out. No fluctuation on Flex-6500.
    Clear tone on monitor.
    Alex - DH2ID
  • Ken - WA8JXM
    Ken - WA8JXM Member
    edited February 2017
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    WSJT-X prefers to shift the transmit signal up to keep the audio modulation within normal range (it prefers to operate "split").  Ideal operation for most rigs is to keep the audio below 2K or 2500 Hz, so WSTJ-X will shift the transmit  frequency up 500 or 1 kHz.  You might not even notice this!   Seeing a break point at 3000 Hz is probably an indication of same.

    WSJT-X's control panel (F2 - Radio) has a section for Split Operation.  Have you noticed it ?  Options are "None", "Rig" and "Fake It"  Try different settings there and see if it  helps.

    Ken WA8JXM

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