SNR fluctuation

[Rick, W4XA]

Howdy all, 

I have been noticing a seemingly strange SNR fluctuation when using my MAC book Pro running Linux. (KDE NEON, Ubuntu based, using the Linux applmage) 

When talking to a station in Spokane from Western WA, I have noticed from observing the Reporter (and reports from the receiving station) that my SNR fluctuates from what I would call a fairly "normal" 10-15 dB and then momentarily dropping to 0, -1,-2,-3 Then back up to 10-15dB.

The receiving station reports an extremely LOW ambient noise level (S0-S2) and he tells me that my received signal is steady at S-9 or better all the time.

On my end, his signal is S-9 or better and his SNR at my end never fluctuates more than a few dB (20 or so +/- 3dB) 

When  I switch computers to a rather new ACER Core-i7 laptop running Winblows 11 or use my older (2015) MacBook Pro running Monterey,   His SNR is simlar on my end but MY SNR at his end no longer fluctuates at all or than a few dB 

It seems that my MacBook Running Linux is the problem.

Has anyone else seen something like this?

73/Rick

W4XA

 

[Mooneer Salem]

Hi Rick,

Does the other station hear anything odd with the audio when the SNR drops below 0? For example, any dropouts in the received audio.

Thanks,

-Mooneer K6AQ

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[Rick, W4XA]

Hi Mooneer, 

Actually yes.  The signal strength as observed on the S-Meter doesn't drop or fluctuate much but the SNR at his end does.  Momentarily dropping from 10-12dB  to around 1 or 2dB  and then briefly 0, -1, -2, etc with a little garble before steadily climbing back up to around 10dB or so..  

He said he'd "lose" a couple of words when the SNR was down around  0, -1, -2 etc.

Receiving  on my end, his signal  (IC705 S-Meter)  stays at around S-9 to S-9+10 with little or no fluctuation. And the  SNR hovers around 20-24dB .

When I switched to either the ACER Laptop(WIN11) or the Early 2015 Macbook Pro (Monterey)  his received SNR didn't fluctuate a lot nor did it drop to near zero dB at any time.

It only seems to do this when I'm using the Mid 2012 MacBook Pro (early Intel Core-i7)  running KDE Neon (Ubuntu 24.04)  

I don't have a different laptop to try running Linux on so I am thinking I can blame it on the hardware , but I would like to try it with a different computer running Linux to verify that!

I've been noticing this for quite some time.   Where the SNR at the other end would fluctuate  from 10-15 down to 0  and then asking the other station if my actual received signal level was doing the same thing and he always told me that my signal doesn't fluctuate.   

 I always thought it was due to propagation effects (multi-path, NVIS phase distortion or maybe even a problem in my auto-tuner not making good contact in the roller inductor, or an antenna  etc) but it's always a one-way thing.

This is the first time where I have switched computers to see if it does it with a different computer.

I might try swapping the HD in the newer ACER Core-i7 laptop and installing Linux to see if it still does it.....That'll probably tell me right away if that old MacBook Pro has some other problem.

[Mooneer Salem]

Hi Rick,

Out of curiosity, does building the latest from "master" help at all? (Or alternatively, you can try the latest AppImage, but I know you've had problems with those before: https://github.com/drowe67/freedv-gui/actions/runs/23220637451/artifacts/5976028919) This is an updated version that no longer needs Python, so there should be a performance improvement.

Thanks,

-Mooneer K6AQ

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[Rick, W4XA]

Mooneer, 

I have never "built it" at all and I haven't tried the updated  image.  I don't have a Github login but I'll establish one and give it a try!

I am guessing that maybe the updated one might also work with my older ASROCK mobo and AMD 3 processor too?  Either way, I'll give it a try and let you know how it works!

Tomorrow morning, I am meeting with a small Radio Club locally to do a FreeDV demo at their meeting.  I'm going to bring my MacBook Pro running the MAC OS and my ACER Win11 laptop plus a Bluetooth speaker.

A couple of the Club  members that I have worked on 6m using FreeDV live within a few blocks and will run home so we can use 6m.   I have a small 6m wire dipole that I'll tape to the wall for the demo.  With the IC705 and a couple of watts it should work well using the internal battery!

Thanks again, 

Rick