K3: DSP Bandwidth Limit

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K3: DSP Bandwidth Limit

Elecraft mailing list
Is there any way to expand the (receive) DSP maximum bandwidth beyond 5kHz in AM mode?  I have the 13 kHz roofing filter installed.

73,

Jim K4AXF
K3 #4936
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Re: K3: DSP Bandwidth Limit

Joe Subich, W4TV-4

On 2019-12-13 8:58 AM, Jim Stoneback via Elecraft wrote:
> Is there any way to expand the (receive) DSP maximum bandwidth beyond 5kHz in AM mode?  

No.  It would be ineffective since the audio chain has a
4500 Hz "brickwall" (sharp cutoff) lowpass filter limiting
the audio response (to remove DAC artifacts/aliasing).

> I have the 13 kHz roofing filter installed.

Remember, the DSP display is audio.  5 KHz represents 10 Hz at
RF (IF).


73,

    ... Joe, W4TV

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Re: K3: DSP Bandwidth Limit

k6dgw
Could you explain a little more?

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 12/13/2019 6:19 AM, Joe Subich, W4TV wrote:
> Remember, the DSP display is audio.  5 KHz represents 10 Hz at
> RF (IF).

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Re: K3: DSP Bandwidth Limit

Joe Subich, W4TV-4
On 2019-12-13 1:22 PM, Fred Jensen wrote:
 > Could you explain a little more?

What's to explain?  AM is a double sideband signal - equal width
either side of the carrier with each sideband carrying the same
audio information but inverted in frequency.

A 5 KHz *audio* bandwidth would be equivalent to a 10 Hz RF (IF)
bandwidth.  In fact, the K3/K3S processes DSP at both "IF" (right
after the analog to digital conversion) and again at "AF" (just
before the digital to analog conversion).  For AM, the IF bandwidth
is twice the AF bandwidth ... for SYNC AM, LSB, USB, CW, DATA the
IF bandwidth and AF bandwidth are essentially the same.

73,

    ... Joe, W4TV


On 2019-12-13 1:22 PM, Fred Jensen wrote:

> Could you explain a little more?
>
> 73,
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
>
> On 12/13/2019 6:19 AM, Joe Subich, W4TV wrote:
>> Remember, the DSP display is audio.  5 KHz represents 10 Hz at
>> RF (IF).
>

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Re: K3: DSP Bandwidth Limit

Lyle Johnson
In reply to this post by k6dgw
Fred,

The audio CODECs in the K3 have a 12 kHz sample rate.  This puts the maximum audio bandwidth at 6 kHz.  Practical limits of DSP filtering in the context of the K3 implementation limit audio to 4.5 kHz or so.

Aliasing around the 12 kHz sample rate of the CODECs required that “brick wall” low pass filter as well as additional analog filters after the audio DACs to eliminate those aliasing artifacts.

73 ,

Lyle KK7P (at the Grand Canyon)


Sent from my iPhone

> On Dec 13, 2019, at 11:24 AM, Fred Jensen <[hidden email]> wrote:
>
> Could you explain a little more?
>
> 73,
> Fred ["Skip"] K6DGW
> Sparks NV DM09dn
> Washoe County
>
>> On 12/13/2019 6:19 AM, Joe Subich, W4TV wrote:
>> Remember, the DSP display is audio.  5 KHz represents 10 Hz at
>> RF (IF).
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
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>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
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Re: K3: DSP Bandwidth Limit

Bill Weaver
In reply to this post by Joe Subich, W4TV-4
 
 
Joe, I think the confusion might come in with the typo ->   A 5 KHz *audio* bandwidth would be equivalent to a 10 Hz RF (IF)
 
Should be ->   A 5 KHz *audio* bandwidth would be equivalent to a 10 KHz RF (IF)
 

 
73,
 
Bill WE5P
 

 
 
 
 

 
 
 
 
 
>  
> On Dec 13, 2019 at 15:31, Joe Subich, W4TV  <[hidden email]>  wrote:
>  
>  
>  On 2019-12-13 1:22 PM, Fred Jensen wrote:  >  Could you explain a little more? What's to explain?
>  
     
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Re: K3: DSP Bandwidth Limit

k6dgw
In reply to this post by Lyle Johnson
OK, I think I read something into Joe's post that wasn't really there,
that's how I thought it worked and I I think Joe was referring to the
DSB BW at the 15 kHz 2nd IF.  Enjoy the GC, we stayed in a cabin maybe
50 meters from the edge ... awesome!

73,
Fred ["Skip"] K6DGW
Sparks NV DM09dn
Washoe County

On 12/13/2019 12:33 PM, Lyle Johnson wrote:

> Fred,
>
> The audio CODECs in the K3 have a 12 kHz sample rate.  This puts the maximum audio bandwidth at 6 kHz.  Practical limits of DSP filtering in the context of the K3 implementation limit audio to 4.5 kHz or so.
>
> Aliasing around the 12 kHz sample rate of the CODECs required that “brick wall” low pass filter as well as additional analog filters after the audio DACs to eliminate those aliasing artifacts.
>
> 73 ,
>
> Lyle KK7P (at the Grand Canyon)
>
>
> Sent from my iPhone
>
>> On Dec 13, 2019, at 11:24 AM, Fred Jensen <[hidden email]> wrote:
>>
>> Could you explain a little more?
>>
>> 73,
>> Fred ["Skip"] K6DGW
>> Sparks NV DM09dn
>> Washoe County
>>

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Re: K3: DSP Bandwidth Limit

Don Wilhelm
In reply to this post by Elecraft mailing list
Jim,

It is important to realize that the K3 bandwith is equal to the audio
bandwidth.  The K3 reports the audio bandwidth.

A K3 with a 6 kHz filter is limited to a maximum of 3 kHz audio because
an AM signal is double sideband and the IF bandwidth for the AM signal
must be twice the audio frequency of the filter.

So an IF filter of 6 kHz is required to obtain an audio frequency of 3 kHz.

The DSP frequency band is in the audio spectrum while the IF filter is
in the RF spectrum.  There is a 2:1 relationhsip in the bandwidth. For
an IF bandwidth (the filter bandwidth) of 6 KHz, the expected audio
bandwidth (shown by the K3S audio bandwidth) is limited to 3 kHz.

Yes, the audio bandwidth displayed can go up to 4000 Hz, but little will
be heard above 3000 Hz with a 6 kHz filter usd for AM.

73,
Don W3FPR

Fn 12/13/2019 8:58 AM, Jim Stoneback via Elecraft wrote:

> Is there any way to expand the (receive) DSP maximum bandwidth beyond 5kHz in AM mode?  I have the 13 kHz roofing filter installed.
>
> 73,
>
> Jim K4AXF
> K3 #4936
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
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>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
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>
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