FM mode coherent modes missing now?

[rsku...@gmail.com]

It's been a while since I messed with FM but there used to be coherent detection modes available. They are not there now. I see the FM0 to FM3 modes, but the coherent modes that were next to the RAT box are no longer there.

Was that by design or am I missing something? I know they were there a while back.

Rick Kunath, K9AO

[Leif Asbrink]

Hello Rick,

The Coh modes were actually in place, but that was not shown on screen.
I have corrected, hopefully I did not introduce new errors....

73
/Leif

> --
> There is an excellent Linrad User Guide by Gaetan, ON4KHG, at:
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[Rick Kunath]

THanks Leif,

When I click on the coh setting in FM mode and a wide filter width for
commercial FM, not sure if that matters, to turn it on it errors out
with this:

lir error 873105Segmentation fault (core dumped)

Rick

[Leif Asbrink]

Hello Rick,

Please try an old version. Maybe 04-12. Probably you would get the same error.

The error is triggered by a baseband sampling rate above 105 kHz which
means that memory for a pilot tone is allocated. Today it seems to me
that Coh modes should not be available in FM mode.

You can of course detect FM with Coh2 in AM mode which would give AM in
one ear and FM in the other. It is possible that enabling Coh2 in FM
mode would give the same result as in AM mode. I may have disabled
the normal FM detectors, but I do not remember and the code is rather
complicated so it would take a long time for me to find out.

In case you get something useful by using Coh detection in FM mode
with an old version of Linrad while you can not get the same with the
latest, please give me some details.

In case you find Coh2 useless in FM mode while it works in AM mode
I will remove the Coh button in FM mode, but if it works I will issue
an error message that prevents the user from selecting Coh modes
when the pilot tone memory is allocated.

The page about FM is here:
https://www.sm5bsz.com/linuxdsp/install/fm.htm

"Linrad also offers the possibillity of using a synchronous detector. The mode is
Coh2 and the output is in stereo. The left channel is the AM component and the right
channel is the FM component. Listen to the Coh2 mode output here: nbfmcoh2.mp3
(690240 bytes) Use ear-phones or an audio player that allows you to select either
the left channel or the right channel."

From this I get the impression that it might work in FM mode, but maybe it
is only working in AM mode. I do not have appropriate hardware running
so it would be non-trivial for me to try it out.

73

Leif

> --
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[Rick Kunath]

Will do Leif and I'll let you know.

It'll be a bit but I'll experiment and see :)

Thanks again.

Rick Kunath, K9AO

[Rick Kunath]

Leif,

What's a good commit number for that 4-12 and an older version for the
Coh testing?

I want to grab the source to keep it separate here for testing.

Thanks again,
Rick

[Leif Asbrink]

Hello Rick,

Here you can get the source code as a .tbz file:
http://sm5bsz.com/linuxdsp/linroot.htm
It is dated Feb 1 2017 but I do not know what number it would
correspond to in the repo. Maybe r756 from Jan 24 2017.

It does not matter which one you try, they are probably all the same
in what regards Coh modes in FM. 04-12 does not compile under Debian 12,
the latest compiler is picky on what it thinks can cause buffer overflows
for strings. Just increase the sizes for those buffers it complains about
or tell the compiler in Makefile to ignore warnings - or use Windows.

73

Leif




> Leif,
>
> What's a good commit number for that 4-12 and an older version for the 756

> Coh testing?
>
> I want to grab the source to keep it separate here for testing.
>
> Thanks again,
> Rick
>

> --
> There is an excellent Linrad User Guide by Gaetan, ON4KHG, at:
> http://w3sz.com/Linrad%20Installation%20&%20Configuration%20User%20Guide%20-%20V1-0.pdf
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[Rick Kunath]

I did some testing on the old Linrad release file Leif, but I was using
your recorded FM file because that 4.x version is pre-Franco adding in
the SDRplay3 support. So nothing conclusive there. I couldn't run
version 4.x live here.

Then I decided to do some testing on the latest Linrad 6 version. I knew
not to use the coherent modes on wide FM. But the FM modes 0 through 3
work well on version 6 on Wide FM. I just had to reduce the first mixer
bandwidth reduction to 2 to get the secondary waterfall wide enough to
drag the filter out for the wide FM stations.

Then I tested on narrow-band FM signals up around 29.6 MHz on 10-meters.
I wound up using a first mixer bandwidth reduction of 6 like I do on AM
mode. That got the secondary waterfall zoom to where I wanted it.

So, some very interesting results on narrow-band FM. The FM modes 0
through 3 did as expected and they  improve the clarity of weak signals,
with FM3 having the best effect on signals at the noise level. But with
the FM mode set to 0 (does that even matter if coherent detection is on
or not?) and selecting coh2 (guessing because I can't see the buttons,
but the usual 2 button presses) and RAT at 36, boom the signal went from
barely readable on FM3 (unreadable on 0, 1, or 2) to easy comfortable
copy. It was an amazing improvement in that the signal went to very nice
copy from darned near at the noise level on FM3, not really comfortable
copy at all. It amazed me as I switched back and forth to see the
startling improvement.

So, for me, I'd say leave the coherent modes in for FM. I don't know if
there is a way to disable them in wide bandwidths to avoid the pilot
filter crash or not. But we can work around that if we know how to use
the coherent detection properly.

This was a lot of fun and very interesting...

Rick Kunath, K9AO

[Leif Asbrink]

Hello All,

Yesterday I uploaded a video about notches in Linrad:
https://www.youtube.com/watch?v=DN26ek8kAe8

The number of notches is limited to 9 and the way to set them
is not very elegant, but they do allow reception that would
otherwise be impossible.

73

Leif

[Rick Kunath]

Very nice Leif, thank you.

A question, what is that little white sort of a "dash" looking indicator
that is moving up and down next to what I thought was the volume control
with the red slider at the left of the green lined spectrum?

Is it AGC, I thought you called it that in the video?


And then directly to the left of that at the right side of the red lined
spectrum, what is the vertical indicator that has the multi-colors at
the bottom and white at the top
?
Rick Kunath

[Leif Asbrink]

Hello Rick,

The little white "dash" is a power meter for the baseband signal.
The colours at the right hand side of the high resolution graph,
red dB scale, is the colours used in the main waterfall. In dB
as indicated by the scale at the left hand side.

/ Leif

> --
> There is an excellent Linrad User Guide by Gaetan, ON4KHG, at:
> http://w3sz.com/Linrad%20Installation%20&%20Configuration%20User%20Guide%20-%20V1-0.pdf
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[Leif Asbrink]

Hello Rick,

The latest version on the repo, r1078 has the Coh and Rat buttons visible.
I will make them disappear when the bandwidth is too large.

73

Leif

> --
> There is an excellent Linrad User Guide by Gaetan, ON4KHG, at:
> http://w3sz.com/Linrad%20Installation%20&%20Configuration%20User%20Guide%20-%20V1-0.pdf
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[Rick Kunath]

Superb Leif,

Thanks so much :)

Rick Kunath