I should point out that my original evangelism of Open Source digital voice
codecs, which nudged David to revisit his thesis, was directed toward
replacing the ones used on VHF/UHF. We do have definite performance
advantages there given SDR radios rather than FM modulators and detectors.
Adoption of this has been delayed due to the necessity to manufacture our
own radios.
HF is low hanging fruit in that we don't have to modify the radios. Beating
SSB for DX use is a great metric to pursue, and seems to be motivating
David to do much fruitful research.
I advised Flex on establishing the API. It was a goal that third parties be
enabled to add and modify the applications on the Open side, including ones
not related to the FreeDV/Codec2 project. It is perfectly reasonable for
someone who is motivated to do so to contribute work to the Flex platform.
Their internal staff are available to talk with us if necessary.
Thanks
Bruce
On Tue, Feb 7, 2017 at 12:25 PM, David Rowe <[email protected]> wrote:
> Hi Helmut,
>
> Lol you won't get stoned - I welcome all opinions.
>
> I share your goal of a digital mode that outperforms SSB at low SNR.
> It's a tough goal, there are good reasons why SSB has been dominant for
> 50 years.
>
> Could you please tell me more about your tests? In particular I'm
> looking for feedback on 700C. A/B samples would be very useful, e.g off
> air recordings of 700C followed by SSB over the same channel.
>
> My experience locally is 700C it's more robust than FreeDV 1600, but I
> have had some situations where SSB worked when FreeDV 700C didn't. I
> have also had some experiences of error free 700C when SSB was right
> down in the noise.
>
> Walter, KW5H, and a team of Hams testing FreeDV 700C in the US have been
> making contacts over paths as long as 2500km, and have consistentl
> experiences of 700C working when SSB was unreadable.
>
> By piecing together our experiences (and especially samples) we can
> improve FreeDV. For example if 700C doesn't work for you Helmut, but
> does for Walter - lets explore the differences and find out why.
>
> Cheers,
>
> David
>
> On 08/02/17 02:03, Helmut wrote:
> > Hi David and all,
> >
> > I think it’s up to Flex to correct their smart-sdr software to make
> freeDV
> > mode 1600 available on the both sidebands depending on the particular
> band.
> > That’s a standard DSP application.
> > To stimulate Flex and others like John Melton and his pihpsdr to
> implement
> > all modes of freeDV is a more critical action: We spent many hours and
> > enthusiasm trying to evaluate objectively the different freeDV modes in
> the
> > real world of our HF bands. No significant improvement concerning
> > readability, resistance to low SNR, fading, Doppler and jamming could be
> > observed. In our mind freeDV is currently a nice experimental platform,
> but
> > no severe competition to SSB. To try to change this situation with
> > measureable and necessary benefits should be the goal. To make digital
> voice
> > e.g. reliably decodable when SSB fails would be great. Maybe the more
> > effective approach is to keep and apply 2.700 kHz bandwidth but to
> increase
> > redundancy.
> >
> > Ok, here I’m ready for stoning.
> >
> > 73, Helmut, DC6NY
> >
> >
> > -----Ursprüngliche Nachricht-----
> > Von: David Rowe [mailto:[email protected]]
> > Gesendet: Dienstag, 7. Februar 2017 09:29
> > An: [email protected]
> > Betreff: [Freetel-codec2] Flex and FreeDV
> >
> > It's been a while since Flex released their support for FreeDV. Walter
> > K5WH, and I have contacted them recently and it turns out the API that
> > it used to integrate FreeDV is open source and available here:
> >
> > https://github.com/n5ac/smartsdr-dsp
> >
> > I really can't stretch to cover this one, I'm already working on codecs,
> > modems, and the FreeDV GUI program.
> >
> > Can some one else please step up and work on getting the Flex support
> > for FreeDV up to date? Plenty of email support available from myself
> > for the FreeDV side and the good people at Flex for their side of the
> API.
> >
> > Thanks,
> >
> > David
> >
> > On 04/02/17 13:14, David Rowe wrote:
> >> Thanks Glen, food for thought....
> >>
> >> On 04/02/17 11:02, glen english wrote:
> >>> ham systems , that are SNR limited, not bit rate limited, will ALWAYS
> be
> >>> a better bet with a constant envelope signal, compared to a linear
> >>> signal (non constant amplitude signal) in terms of power output power
> >>> amplifier UTILIZATION. Utilization is the key here.....
> >>>
> >>> for systems that need to push a large bit rate through a narrow
> channel,
> >>> there is little option but a QUAM signal.
> >>>
> >>> There is no disadvantage of a constant envelope signal compared to a
> >>> linar signal with regards to multipath protection, mitigation, dopplers
> >>> etc PROVIDING THAT the signal chain is linear on receive.
> >>>
> >>> That is to say, after limiting a signal, information has been thrown
> > away.
> >>>
> >>> So, not to get confused with a constant envelope signal with FM demod.
> >>> results are poor compared to using a linear demod.
> >>> **********
> >>>
> >>> David, it is worth a look at GSM
> >>>
> >>> GSM has a training sequence each frame and deals with multipath (up to
> >>> the training length) very well. multipath can improve the SNR.
> >>>
> >>> constant envelope, non linear TX, linear RX.
> >>>
> >>>
> >>> g
> >>>
> >>>
> >>>
> >>> On 4/02/2017 10:37 AM, David Rowe wrote:
> >>>> Thanks Steve, there was error in the
> >>>
> >>>
> >>>
> >>>
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