On 9/18/2024 1:28 PM, David Norris wrote:

[This followup was posted to uk.radio.amateur and a copy was sent to the cited author.]

When I first got into the digital modes, starting with DMR (Fusion and
D-Star came later) I published a lot about them on my website. This
includes what, on 24/12/2015 became the world's first review if the AOR AR-DV1.

I wanted to point out that all the aterial is now back on a new server.

I am also active on the 'Network Radio' channels too.

I am operating currently from China.

The URL can be found here: https://dfdn.info/radio

David, G7VDI

OMG no

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In message <MPG.4155484e2f2844a7989683@news.eternal-september.org>,
David Norris <norrisdavid1297@gmail.com> writes

[This followup was posted to uk.radio.amateur and a copy was sent to
the cited author.]

When I first got into the digital modes, starting with DMR (Fusion and
D-Star came later) I published a lot about them on my website. This
includes what, on 24/12/2015 became the world's first review if the AOR >AR-DV1.

I wanted to point out that all the aterial is now back on a new server.

I am also active on the 'Network Radio' channels too.

I am operating currently from China.

The URL can be found here: https://dfdn.info/radio

David, G7VDI

What CNR can DMR modes work down to ? Is there a threshold like what
FM has or does it degrade gracefully ? I've never seen a proper
technical article on it. Is it a synchronous direct
modulation/demodulation scheme ?

Closest I can find

<https://www.alcom.ca/downloads/tait/whitepapers/coverage-technology-comp arison-dmr-v-analog-nbfm-white-paper.pdf>


I tried this on the 146-148 MHz a while back, but it didn't work well.

Https://freedv.org/

Brian
--
Brian Howie

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On Thu, 19 Sep 2024 08:04:41 +0100
brian <nospam@b-howie.co.uk> wrote:

What CNR can DMR modes work down to ? Is there a threshold like
what FM has or does it degrade gracefully ? I've never seen a
proper technical article on it. Is it a synchronous direct modulation/demodulation scheme ?

Closest I can find

<https://www.alcom.ca/downloads/tait/whitepapers/coverage-technology-comp arison-dmr-v-analog-nbfm-white-paper.pdf>

DMR (using C4FM modulation) provides better BER below the point at
which FM has rough noise and poor intelligibility but there is a sudden
cutoff as signal drops and the error rate exceeds the ability of the FEC
scheme to correct such gross error rates.

I tried this on the 146-148 MHz a while back, but it didn't work
well.

Https://freedv.org/

Using HF SSB current freedv 700D mode is capable of providing a low
enough error rate for reasonable quality speech at an SNR of -2dB,
reasonable quality is of course somewhat subjective but the speech is
recovered by means of FEC. The underlying modulation is QPSK on
multi-carrier OFDM with a bandwidth of about 1kHz.

There should be more information in David Rowe's blog articles at
freedv.org

Development is ongoing with new modes being tested on air at present by
a test group.

--

Brian Morrison "No, his mind is not for rent
To any god or government
Always hopeful, but discontent
He knows changes aren't permanent
But change is"

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