CW filter and Roofing filter

[dennis rosenbalm]

Trying to sort this out.......
1) with any filter selected using the XFIL button on the K3, there is only ONE crystal IF filter in the signal path. In other words, there is no cascading or tail ending of the filters before and after the IF.
2) if I select a 400 Hz filter with the XFIL button then adjusting the DSP WIDTH control to any WIDER than 500 Hz is pointless.
3) can the DSP be bypassed to produce a purely analog demodulated audio to the speaker? As I recall years ago, some early DSP radios had this feature. I am pretty sure the answer is no but still, had to ask.
It is interesting to note that there are new hams out there who have never listened to an analog receiver before. It can be an eye opening experience!
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[Don Wilhelm-4]

Gee,

The K3 DSP cannot be bypassed, it is part and parcel of the K3.  The DSP
mathematical computations are what does the modulation, demodulation,
and forms the filters as well as doing a lot of other tasks.  The K3 DSP
processing in the K3 is done at a frequency of 15kHz.
There is no parallel to an analog receiver.  The front end of the K3 is
analog, but as soon as the signal is converted to 15kHz, it goes through
an ADC and becomes 'mathematical soup' - after processing, the math
result is fed to a DAC where it emerges as audio.  In other words, the
K3 is an SDR with an analog front end and a built-in processor.

The K3 must have the 2.7 or 2.8kHz filter installed.
If you have additional hardware filters installed, they are not cascaded
- BUT the roofing filter can cascade with the DSP filter. Even if you
select a narrow filter with the XFIL button, if you widen the DSP
bandwidth beyond the width of that narrow filter, the K3 will switch to
a wider filter.

I hope that helps your understanding.

73,
Don W3FPR

On 6/24/2015 8:55 AM, Gee wrote:
> Trying to sort this out.......
> 1) with any filter selected using the XFIL button on the K3, there is only ONE crystal IF filter in the signal path. In other words, there is no cascading or tail ending of the filters before and after the IF.
> 2) if I select a 400 Hz filter with the XFIL button then adjusting the DSP WIDTH control to any WIDER than 500 Hz is pointless.
> 3) can the DSP be bypassed to produce a purely analog demodulated audio to the speaker? As I recall years ago, some early DSP radios had this feature. I am pretty sure the answer is no but still, had to ask.
> It is interesting to note that there are new hams out there who have never listened to an analog receiver before. It can be an eye opening experience!
>

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[Arie Kleingeld PA3A-2]

Cascading:
The only cascading filtering is first the xtal filter and then the DSP
filter. (So there's only one xtal filter)

400Hz-500Hz:
Yes listening to a wider DSP filter than Xtal filter is pointless.
Although (if configured correctly) the K3 will switch to a wider Xtal
filter (if there is one) if you widen up the DSP.

Analog demodulation:
Demodulation in the K3 is DSP. There is not menu setting to get around this.


73
Arie PA3A

Gee schreef op 24-6-2015 om 14:55:

> Trying to sort this out.......
> 1) with any filter selected using the XFIL button on the K3, there is only ONE crystal IF filter in the signal path. In other words, there is no cascading or tail ending of the filters before and after the IF.
> 2) if I select a 400 Hz filter with the XFIL button then adjusting the DSP WIDTH control to any WIDER than 500 Hz is pointless.
> 3) can the DSP be bypassed to produce a purely analog demodulated audio to the speaker? As I recall years ago, some early DSP radios had this feature. I am pretty sure the answer is no but still, had to ask.
> It is interesting to note that there are new hams out there who have never listened to an analog receiver before. It can be an eye opening experience!
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
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> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to [hidden email]
>

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[k6dgw]

On 6/24/2015 5:55 AM, Gee wrote:
> with any filter selected using the
> XFIL button on the K3, there is only ONE crystal IF filter in the
> signal path.

Correct

> In other words, there is no cascading or tail ending of
> the filters before and after the IF.

Semi-correct.  If by filter you mean crystal roofing filter, and if by
IF you mean 1st IF [8 MHz], correct.  One roofing filter followed by 2nd
IF filtering provided by the DSP.

  2) if I select a 400 Hz filter
> with the XFIL button then adjusting the DSP WIDTH control to any
> WIDER than 500 Hz is pointless.

Sort of.  The K3 will automatically select a roofing filter from
whatever you have that is wider than what the DSP is set to ... if it can.

  3) can the DSP be bypassed to produce
> a purely analog demodulated audio to the speaker?

No.  Once the 15 KHz 2nd IF becomes number soup in the DSP, there are
only two analog things left in the chain:  The AF amplifier and you.
The DSP contains a lot more than just adjustable filtering, such as AGC
and demodulation.

> It is interesting to note that
> there are new hams out there who have never listened to an analog
> receiver before.

True

 >It can be an eye opening experience!

Possibly, although I doubt most would find that.

73,

Fred K6DGW
- Northern California Contest Club
- CU in the 50th Running of the Cal QSO Party 3-4 Oct 2015
- www.cqp.org

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