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K4 Observations

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David Woolley (E.L)

Re: Sensitivity - Was K4 Observations

These techniques all end up using more bandwidth than a simple scheme,
and the larger bandwidth itself increase the N in SNR.

There is actually a theory for the case of idealised white noise and no
other degradation (both of which are likely to be assumed in the cases
previously discussed), that sets a theoretical limit to the error free
digital communication rate of channel, based on bandwidth and SNR. This
is the Shannon - Hartley theorem, and states that the capacity in bits
per second is:

bandwidth * log2 (1 + Signal / Noise)

Note that this formula still has a positive result even if the signal is
only minutely greater than zero.

The holy grail of communications coding is to get as close as possible
to this without having excessive latency.

Maybe a better figure of merit for these, "below the noise" digital
systems would be to quote the channel capacity as a percentage of the
Shannon limit. I think the system used for 5G mobile phones get very close.

One does have to be careful with bits per second, as I understand that
FT8 relies on some parts of transmissions carrying less bits than needed
to encode the characters in the standard code used, e.g. the number of
bits actually represented by a call sign is log2 (number of possible
callsigns) and the number encoded in FT8 is log2 (number of active FT8
callsigns).

--
David Woolley
Owner K2 06123

On 19/05/2019 19:15, Joe Subich, W4TV wrote:

>
> There is one place that digital modes (like those by Joe Taylor and
> associates) can improve the decoded SNR beyond simply reducing the
> detection bandwidth. If the modulation/encoding supports N states
> but the encoding only uses M of those states, the decoding software
> can make use of the "sparse constellation" to recognize states that
> are impacted by noise and select the "closest" valid state.
>
> This "coding gain" can improve the overall SNR beyond that provided
> simply by the "matched" (or optimal) noise bandwidth. However, with
> all amateur modes (CW to FT8 & FT4) the majority of the SNR improvement
> over SSB (or AM) is simply due to the use of optimal bandwidth to
> reduce extraneous noise in the detector bandwidth. Even with SSB,
> properly tailoring the IF bandwidth will make several dB difference
> in the detected SNR. For example, a 2 KHz bandwidth (500 - 2500 Hz)
> can provide significant improvement over a 2.8 KHz bandwidth (200 -
> 3000 Hz) under noisy conditions.

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Tony Estep

Re: Sensitivity - Was K4 Observations

In reply to this post by Jim Brown-10

On Sun, May 19, 2019 at 12:06 PM Jim Brown <[hidden email]>
wrote:

> ... FT8 can work about 10 dB deeper into the noise than CW with good
> radios and very good operators
> on both ends. I've worked a lot of both modes.
>
> On 5/19/2019 6:50 AM, Wes wrote:
> > FT8 reports negative SNRs number but we both know those are bogus....
>
================
For those who care about the relative communications efficacy of various
modes, here's a Joe Taylor document from the archives with some discussion
and analysis, which provides theoretical confirmation of the comments made
above by Jim and earlier by Joe W4TV.
http://physics.princeton.edu/pulsar/K1JT/EME_Florence_2008.pdf
As a side note, we all seen many occasions when FT8 or WSPR could decode
signals that were completely inaudible and invisible on a pan.

73, Tony KT0NY
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Ed K1EP

Re: K4 Observations

In reply to this post by Grant Youngman-2

On Sat, May 18, 2019, 23:45 Grant Youngman <[hidden email]> wrote:

> I think your observations are spot on in most respects.
>
> While the basic K4 is certainly going to be a great radio, it will likely
> NOT have the strong signal handling characteristics of the K3/K3S. There
> will still be the likelihood of A/D clipping suffered by virtually all
> 16-bit SDRs in a high-density RF environment.

I would guess that once a better preforming A/D becomes available and
affordable, a plugin upgrade will be available to replace the current A/D,
similar in concept to the synthesizer upgrades in the K3.
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Drew AF2Z

Re: K4 Observations

Yes, I think Eric mentioned in the video that an upgraded ADC for the K4
might be offered in a few years. Does this mean a higher resolution ADC
(18 or 20 bit)?

73,
Drew
AF2Z

On 05/20/19 08:59, Ed K1EP wrote:

> On Sat, May 18, 2019, 23:45 Grant Youngman <[hidden email]> wrote:
>
>> I think your observations are spot on in most respects.
>>
>> While the basic K4 is certainly going to be a great radio, it will likely
>> NOT have the strong signal handling characteristics of the K3/K3S. There
>> will still be the likelihood of A/D clipping suffered by virtually all
>> 16-bit SDRs in a high-density RF environment.
>
>
> I would guess that once a better preforming A/D becomes available and
> affordable, a plugin upgrade will be available to replace the current A/D,
> similar in concept to the synthesizer upgrades in the K3.
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>

Buck

Re: K4 Observations

I heard that as well. Elecraft's modular construction will allow for
component upgrades as it did with the new synthesizers, thereby
extending the useful life of the radio a couple of generations.

Buck, k4ia
Honor Roll
8BDXCC
EasyWayHamBooks.com

On 5/20/2019 12:30 PM, Drew AF2Z wrote:

> Yes, I think Eric mentioned in the video that an upgraded ADC for the K4
> might be offered in a few years. Does this mean a higher resolution ADC
> (18 or 20 bit)?
>
> 73,
> Drew
> AF2Z
>
>
> On 05/20/19 08:59, Ed K1EP wrote:
>> On Sat, May 18, 2019, 23:45 Grant Youngman <[hidden email]> wrote:
>>
>>> I think your observations are spot on in most respects.
>>>
>>> While the basic K4 is certainly going to be a great radio, it will
>>> likely
>>> NOT have the strong signal handling characteristics of the K3/K3S.
>>> There
>>> will still be the likelihood of A/D clipping suffered by virtually all
>>> 16-bit SDRs in a high-density RF environment.
>>
>>
>> I would guess that once a better preforming A/D becomes available and
>> affordable, a plugin upgrade will be available to replace the current
>> A/D,
>> similar in concept to the synthesizer upgrades in the K3.
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[hidden email]
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>>
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html