"Hum" on Carrier - Very odd

[AB5N]

Greetings folks-

I started having trouble with stations not being able to decode my Olivia transmissions using FLdigi
and the VAC409 cables. Thetis version 2.9.0.6

Lands up my signal is not clean. It has another low freq audio signal superimposed on it. Looks like 60 hz hum possibly.
Is it possible at all that 60 cy hum could get onto the signal due to a ground loop in the AC wiring- in the shack?

I've tried all the obvious things to no avail. Anyone ever see this?

Take a look: https://www.youtube.com/watch?v=MUTZmkW8Oo0

Thanks-
Bob-AB5N

[w-u-2-o]

Not enough information present in your post to debug the problem.

There is no way for hum to get onto the audio if all audio connections are in software. If it's Fldigi<-->Muzy VAC<-->Thetis then you could have all the ground loops in the world and it won't matter.

Virtual audio drivers are often disarranged by Windows updates. This could not cause a hum, but can cause audio to fail to flow at all.

The latest version of Muzy VAC is 4.67. You might as well update as part of the troubleshooting effort. Uninstall VAC. Reboot. Install. Reboot. The reboots are important.

I'm suspicious: does any part of your Fldigi--Thetis audio connection travel through some sort of analog connection?

How do you know the hum is present? In your video it appeared that you might be receiving your own signal on some other receiver. Is that correct? Perhaps it's that receiver that has a hum in it.

This is probably going to get moved to one of the audio sub-forums depending on how the discussion flows...

[AB5N]

1st: Signal seems to have cleared up. Clean sine-wave now. I have a complex system here running house AC
and battery power. I've had a hot neutral AC line earlier (fixed 2 yrs ago) and it is easy to get a ground loop here.

To compound it, the 7000 DLE II I received had the case factory painted such that the
case was not grounded to the circuit boards. The areas under the screw heads (and BNC's) were fully painted black.
All the antenna grounds - as well as the grounding post - were floating. I had terrible RF feedback problems
and had to bond everything together to be able to use the radio.

Thanks for your answer and help. All good now.

Bob-AB5N

[rdwing]

It's unclear to me, how did you resolve the problem?

[kc2rgw]

A tip. VAC can glitch on initial start or a mode switch if sampling and buffer sizes change.

I test the sound simply by ear by enabling Mon, transmit to the dummy load and see if the sound is clean. For digi I send a data stream to hear it modulated vs just a carrier.

If it’s dirty sounding you can check the audio tab and look for over/underruns, as you’ll see a lot of them accumulating if this is the issue.

The fix can be by toggling VAC on and off or sample rate and buffer size to other values or if that doesn’t work, a restart of Thetis can fix it too.

The latest releases have been far more stable in this regard.

Also I discovered that Windows will just randomly break digital audio drivers (in this case the virtual audio cables, in my case Voicemeeter mixer) and ripping them out and reinstalling will fix things. This can happen with in place major version upgrades or the periodic jumbo patch intervals in Windows.

Another tip is the USB mic interface drivers for voice. The drivers provided by Windows are not as good as those from the manufacturer for Motu and for Focusrite. They aren’t as stable or perform as well. This only applies for VAC with a USB mic interface.

[w-u-2-o]

Bob's problem had nothing to do with VAC.

[kc2rgw]

How is he running fldigi without VAC?

[w-u-2-o]

He's not running it without VAC. But that has nothing to do with it. He had a basic bonding and grounding problem at his station which affected the quality of the transmitted RF. Probably power supply related. You can't get hum on a VAC connection. Reread the entire topic.

[kc2rgw]

Well when VAC is not right and glitches it transmits artifacts in digi modes that people mistake for a carrier.