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DSP and the KX3

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Phil Hystad-3

DSP and the KX3

For you KX3 signal processing experts and the algorithms implemented for the KX3?

Is there any work to clean up an actual SSB signal to make it more intelligible in cases of various phase changes or interference via reflections (ionosphere). I mean, a slightly warbled signal cleaned up to reduce or eliminate that kind of distortion?

I am not even sure if or how this can be done as my experience in signal processing is certainly not up to that level but it seems that it may be possible.

No, this is not because I am having a problem with my KX3, it is a question asked by a friend of mine so I am relaying it here.

73, phil, K7PEH

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wayne burdick

Re: DSP and the KX3

Administrator

Hi Phil,

The KX3 (and K3) both provide several ways to make speech signals more intelligible in the face of noise or reflections, including NR (stochastic noise reduction), NB (impulse blanking), and passband shift/width adjustment. I'm not sure that compensation for multipath distortion is possible or even desirable, but it's an interesting question.

73,
Wayne
N6KR

On Feb 5, 2014, at 2:48 PM, Phil Hystad <[hidden email]> wrote:

> For you KX3 signal processing experts and the algorithms implemented for the KX3?
>
> Is there any work to clean up an actual SSB signal to make it more intelligible in cases of various phase changes or interference via reflections (ionosphere). I mean, a slightly warbled signal cleaned up to reduce or eliminate that kind of distortion?
>
> I am not even sure if or how this can be done as my experience in signal processing is certainly not up to that level but it seems that it may be possible.
>
> No, this is not because I am having a problem with my KX3, it is a question asked by a friend of mine so I am relaying it here.
>
> 73, phil, K7PEH
>
>
> ______________________________________________________________
> Elecraft mailing list
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wayne burdick

Re: DSP and the KX3

Administrator

Of course I meant "in the face of noise or interference…." Not sure how "reflections" snuck in there.

Wayne

On Feb 5, 2014, at 2:59 PM, Wayne Burdick <[hidden email]> wrote:

> Hi Phil,
>
> The KX3 (and K3) both provide several ways to make speech signals more intelligible in the face of noise or reflections, including NR (stochastic noise reduction), NB (impulse blanking), and passband shift/width adjustment. I'm not sure that compensation for multipath distortion is possible or even desirable, but it's an interesting question.
>
> 73,
> Wayne
> N6KR
>
>
> On Feb 5, 2014, at 2:48 PM, Phil Hystad <[hidden email]> wrote:
>
>> For you KX3 signal processing experts and the algorithms implemented for the KX3?
>>
>> Is there any work to clean up an actual SSB signal to make it more intelligible in cases of various phase changes or interference via reflections (ionosphere). I mean, a slightly warbled signal cleaned up to reduce or eliminate that kind of distortion?
>>
>> I am not even sure if or how this can be done as my experience in signal processing is certainly not up to that level but it seems that it may be possible.
>>
>> No, this is not because I am having a problem with my KX3, it is a question asked by a friend of mine so I am relaying it here.
>>
>> 73, phil, K7PEH
>>
>>
>> ______________________________________________________________
>> 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
> 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

Phil Hystad-3

Re: DSP and the KX3

In reply to this post by wayne burdick

Wayne,

Thanks for the quick reply. My friend and I were discussing ways of doing this (that is, sending/receiving clear voice with DSP helps) and then I decided that it has been done. Well, not by the K3 because it does not digitize the actual signal being sent but I was thinking of D-Star and its use with repeaters. I wonder how wide that digital signal is, maybe you know. D-Star on HF might be too wide.

73, phil, K7PEH

On Feb 5, 2014, at 2:59 PM, Wayne Burdick <[hidden email]> wrote:

Lyle Johnson

Re: DSP and the KX3

It is, look up FreeDV and the open source CODEC being used with it for
HF applications. I think there was some discussion of all this on this
reflector a couple months back, you might want to do a search for it.

73,

Lyle KK7P

> ...I was thinking of D-Star and its use with repeaters. I wonder how wide that digital signal is, maybe you know. D-Star on HF might be too wide.

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george fritkin

Re: DSP and the KX3

What is needed is complete digital voice transmission. Of course you would lose the personal touch on SSB but one could make weak signal operation somewhat better. With encryption keys, you could talk to your buddies in complete confidence. Gee what would the guys on 75 and 20 do if they lost their audience??

Perhaps the new K? could incorporate that function

George, W6GF

PS Please don't!!!!

On Wednesday, February 5, 2014 4:40 PM, Lyle Johnson <[hidden email]> wrote:

It is, look up FreeDV and the open source CODEC being used with it for
HF applications. I think there was some discussion of all this on this
reflector a couple months back, you might want to do a search for it.

73,

Lyle KK7P

> ...I was thinking of D-Star and its use with repeaters. I wonder how wide that digital signal is, maybe you know. D-Star on HF might be too wide.

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DL6OAP

Re: DSP and the KX3

The main approach for solving the multipath problem would be a long symbol duration and some interleaving for error correction. The symbols should be longer than a typical delay between two paths.

Since the phase measurements on a typical hf channel cannot be very sensitive because of noise, the symbol would be distributed on several simultaneous carriers (that is the approach used e.g. in DRM digital shortwave broadcast and in the european DVB-T television standard - and FreeDV without the interleaving). Long symbols plus interleaving would introduce some delay into the communication.

FreeDV uses (I believe) 14 carriers (differential phase keying) and roughly 1500 bits/sec, resulting in a symbol length of 10 ms which is in the order of magnitude of a typical multipath delay (as reported by VOACAP propagation software or by the DRM channel analysis graph in Dream) Since FreeDV does not use any interleaving for error correction, the only delay is the symbol length (plus some processing time). I guess the individual carriers would need a signal/noise ratio that is similar to one of the PSK (maybe PSK125?) modes in order to be reliably detected.

The problem is, the multipath delays on the channel (in time) correspond to a sum of sine functions in "frequency space" - if two paths are about the same strength, they could completely "interfere out" on some frequencies causing individual carriers disappearing in the noise - I have no idea what FreeDV does if one carrier is completely missing.

This same problem occurs with analog signals. Much of the information transported by the voice consists of the relative phase/amplitude relations of the pitch (fundamental frequency of the voice) and its higher harmonics (this is basically the largest fraction of the information the FreeDV Codec converts into a bitstream). If your channel destroys this information by taking many (or the most significant) of the higher harmonics out, you can not read the audio any more. If the individual harmonics are not burried in the noise, it should however be possible to restore amplitude/phase information by applying the "reverse" of the transfer function of the hf channel to the signal in Fourier space. Maybe, a kind of "equalizer" that not only aligns the frequency bands but also the relative phases could be used. The main problem is the large number of parameters you would have to align (two per aditional path - one corresponding to the delay plus one corresponding to a relative ampl
itude), if more than two paths are present.

However, I am no expert in DSP, and not sure if this approach would result in a "causality problem"...

Greetings

Ralf, DL6OAP

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