The Curious Case of the Wandering Audio Output Level

It was a dark and stormy night.

Although not strictly recording and guitars I thought the sleuths here may have some ideas...

I have a curious case of wandering output power on a radio transmitter set up.

This is a digital radio system that uses the sound card to decode and generate the digital tones. The output audio level translates directly to transmitted output power, i.e. if you turn up the volume the transmitter power increases, decrease the volume power decreases.

A little while back I upgraded the laptop I use to run the software to Windows 10.

The upgrade from Windows 8.0 was long overdue and was prompted by several apps I use no longer offering support on Windows 8.

The upgrade was not without issues but after a few hours farnarkling about a workable platform was in place.

So off to the shack and onto the airwaves.

Over the last few weeks I have noticed that I have to keep an eye on both my output power and ALC meters while the system is transmitting. The output power wanders, sometimes up and sometimes down without any knowing changes from me.

An adjustment of the output power slider in the software (WSJT-X if anyone is interested) and all settles for a while.

I suspect that the Win10 audio driver and built in audio card may be causing the wander. Prior to the OS upgrade the driver had both the windows driver and an OEM driver for the sound card, there is no Win10 OEM driver available, so the Windows driver is the one in use. It recognises the card and seems to (otherwise) operate correctly.

I am awaiting an el cheapo external USB sound card, well a $20 one - not the $4 one. The thought is to move the audio I/O that the software is using onto the external card to eliminate the Win10 driver and internal card from the set up.

(A thought occurred while typing this - why wait for the external card? Why not use the USB mixer I have sitting idle in the other room? Tomorrow may see that experiment).

Has anyone come across this audio level wander before?

I can understand the output audio (and therefore power) changing slightly as the output frequency is moved up or down the spectrum this being a function of the generated tones vs the frequency response of the sound card but the wandering happens without any such change.

Hmm... Ham radio on a guitar forum.... but it's an audio interface issue and that has relevance to many guitarists....

Your suspicion that it's the windoze driver is probably correct. Main reason being is that the 'generic' driver only provides a basic command set to the audio interface, and many of the more specialized audio interfaces have extra commands that should be set to ensure repeatable and reliable and consistent operation. The correct driver will ensure these extra or unique commands are set to prescribed values during use thus ensuring consistent operation.

The extra or unique commands could be offset values such as left volume vs right channel volume. They may be bias or attenuator settings for the amplifier in the audio output or input, or a myriad of other possible options that should be and are set by the correct driver but are not necessarily and consistently set by the generic windoze driver.

The fact that it works at all casts doubt it's your hardware causing the problem.

Good luck with the new USB sound card. I'd be interested in getting one if it works and trying a bit of WSJT-X or maybe WSPR on 40m.

DE... VK4TMH

Hi Marcel,
I was hoping you might chime in.

I have actually posted this on an AR forum but I think the nuance of audio and sound cards has them out of their comfort zones.

Once the mowing and such are dispensed with today, I hope to get some shack time and see if I cant jury rig a connection via the Behringer USB mixer I remembered last night.

I'll report back one way or the other...

THX
73
DE VK2CSW

The most reliable USB audio interface to radio that I have used is the Tigertronics Signalink....Too expensive for me at the moment but it has a great PTT and RX ports that work with any radio.... A AU$20 version would be awesome... Somehow I doubt the Behringer has a PTT out....

No it doesn't have PTT but I use CAT port control for PTT so it isn't a drama (Yaesu FT-857D).

The audio interface is a homebrew job that is essentially two line isolation transformers to insert a gap between radio and PC soundcard for earth mismatch potentials.

The CAT control us a USB data connection to the PC on a separate port on the radio.

It looks like the NBN FTTC Modem that was installed on Friday is simply a source of Wideband Noise on the HF bands. The waterfall is hundreds of thin vertical lines.
Power the modem down or unplug it from the lead-in and magically it goes away.

The NBN isn't even fully installed and is already causing issues.

I didn't get around to testing the audio interface.

Have fixed wireless NBN here, so far less issues on HF..... Cheap and nasty 12VDC battery chargers are my biggest HF noise creators.