RTTY Transmit Audio Sounds Awful in Monitor

William Hein

I tried calling K5P on 40m RTTY this morning with MMTTY (latest version), SSDR 1.6.19 and FLEX-6700.

I now know how to set the TX / RX split in a RTTY pileup correctly however I noticed my TX audio sounds awful. I tried headphones, speaker (shielded powered studio monitor) and different DAX TX and monitor audio levels. Didn't make a difference.

My station is well grounded and the antennas are a 150 feet from the shack. I haven't had RFI issues on other modes.

What is causing the distortion in the monitor? Am I transmitting distorted as well (I had to leave for work before I could ask anyone to listen to my tx)?

I have a short video here: https://www.youtube.com/watch?v=FQkpoNqFPoc

Any help appreciated 

73
Bill AA7XT

Stu Phillips - K6TU

Not clear which release you are using but I have experienced this intermittently in the past (not since using 1.6.17 BTW)...

The problem is likely due to a buffer corruption within the DAX driver.  Closing the DAX control panel (which closes all the DAX devices) and then restarting DAX (or a PC reboot) solves the problem.

You can often see the issue on the transmit waveform displayed on TX - it will be very broad and bot have the two clean peaks for the diddles.

Stu K6TU

Ed, K0KC

Bill,

The video shows that your transmit audio level is way too high, likely causing the distortion.

Ed, K0KC

William Hein

What level should I be aiming for in RTTY mode? Note I tried turning the DAX TX drive level way down and it was still distorted even when my TX output dropped to nothing.

I am using SSDR 1.6.17, BTW, my typo on orig post

William Hein

Thanks, Stu. I should have thought to try a reboot. But it was well before dawn and I wanted to work a new RTTY DXCC which usually means I'm not thinking clearly...

Ken - NM9P

I had this happen last night after the rig had been running steady for about a week. Distorted RTTY audio in the monitor and a very raspy, saw-toothed pattern on the panadapter. I closed DAX and opened it again and everything was fine. This was with the new version 1.6.17. No big deal, but it took about 30 seconds for the reset.

Ken - NM9P

After watching your video, I agree that you are driving the audio circuit too hard. Your "Mike level" should never be in the red. On RTTY, keep it at least a notch or two below red level. Adjust it either with the DAX TX level control or the sound card level in Windows.

Stu Phillips - K6TU

With digital, you should aim for a peak indicator reading at -3 dBFS.  The transmit chain is calibrated to generate full output power at this level and still leaves 3dB headroom to avoid clipping.

Aim for the same peak reading on phone modes as well.

Ditto when using the K6TU Remote iPad app.

Stu K6TU

George KF2T

Concur with Ken - overdriving in a digital environment gets nasty quick.

William Hein

Tested RTTY TX this morning after PC reboot and working FB, signal looks and sounds clean. I also backed off drive as advised.

I also confirmed that switching off Auto Switch TX Slice allows me to set my TX / RX split on Slice A or Slice B either way.

Have to say that I really like the new CAT and DAX features now that I've dug into them a bit. Also, really like the RTTY mode implementation and am motivated to jump into a few more RTTY pileups after being generally inactive in this mode for a few years.

73
Bill AA7XT