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With any digital mode AFSK, transmit audio is fluttering/pumping

Discussion in 'Mac Ham Radio on macOS & iOS' started by K7GQ, Dec 21, 2019.

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  1. K7GQ

    K7GQ Subscriber QRZ Page

    I'm encountering a Mac OS High Sierra problem of sorts - though I don't know that High Sierra is causing it. From any digital program, the transmit audio is pumping (up and down) or fluttering causing the transmit output to be unreadable. If I was using VOX, the radio might briefly drop into receive though this symptom is a second or more in duration. I do not use VOX.

    This has recently begun after the latest Security Update (2019-007) a week or so ago (though I don't recall seeing anything about USB in the details).

    I have totally ruled out RFI of any sort. The radio is a K3 using DATA mode (not USB) using the CAT method of PTT.

    The audio output to the K3 is set at near maximum though changing the level through the MIDI utility had no positive effect - actually no effect at all.

    I'm scraping for ideas please ...

    Last edited: Dec 21, 2019
  2. K3DCW

    K3DCW QRZ Lifetime Member #212 Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    There was apparently a fix for some audio issues involving MacBook Pros, but I don't recall anything for USB-related audio.

    Where do you have your K3's audio input set? I no longer have a K3, but as I recall, in the menu there is an option for audio input level. You might try turning that up a fair amount to ensure that sufficient signal strength is making it into the rig. If it is turned down too low, you may simply be putting too little audio into it.

    Also remember, with the K3 you want sufficient audio drive to produce 4-5 bars of ALC action on the K3 display. If you go too low and aim for zero bars, the K3's DSP will start pumping and will introduce distortion.
  3. K7GQ

    K7GQ Subscriber QRZ Page

    Well, I thought you had it. I raised the LINE IN level to nearly max and the radio settled down (it seemed). I answered a FT8 CQ and halfway through the transmit segment, the stuttering began.

    There seems to be a bit of USB strangeness going on here however: my iPhone which is cabled to a USB port periodically announces itself as if it was just plugged in and one needed to provide the security code to permit charging.
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    It may be a ground loop problem.
  5. K3DCW

    K3DCW QRZ Lifetime Member #212 Volunteer Moderator Platinum Subscriber Life Member QRZ Page

    Are you running directly directly from the computer to the K3, or through a hub? Is it a USB connection or perhaps through a Thunderbolt connection? A few years ago, macOS had a serious USB audio issue that I resolved by running through a Thunderbolt Hub which had a USB port. My current setup also uses USB audio to the rig (TS-890s), running off of a USB-C/Thundrbolt 3 connection from which I use a 4-port hub from Anker to run all of my radio connections. No issues there at all with hiccups or the like.

    Probably not the solution you want, but it definitely works.
  6. K7GQ

    K7GQ Subscriber QRZ Page

    I don't think I do but I can't argue against this ... All of the electronics here are on one circuit.

    The K3 audio connection is direct to the computer though I have used a power hub at other times.

    I have apparently solved this issue but have learned NOTHING from it. I replaced a new pair of 3' mini-stereo cables between the K3 and sound card with an older set that were shorter (1'). There is no "aha" moment here though.

    The fact that this fluttering/pumping/motor-boating could occur with the K3 in TEST mode (zero RF output) with cables that were 2' longer doesn't make any sense to me.

    Oh well, I guess I can return to making some enchanting FT# Q's ...
  7. KA0HCP

    KA0HCP XML Subscriber QRZ Page

    Think "Common Mode Current".

    I've seen similar power output pumping with high SWR matches on various bands and two antennas. Chokes and isolation helped.
  8. K7GQ

    K7GQ Subscriber QRZ Page

    so have I but I think you missed the part where this also occurred when the K3 was in TEST mode - that is, zero RF output.

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